Evaluation of Two CEDA 

Weatherization Pilot Implementations 

of an Exterior Insulation and OverClad Retrofit Strategy for Residential 

Masonry Buildings in Chicago 

Ken Neuhauser 

Building Science Corporation 

August 2013 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 

NOTICE 

This report was prepared as an account of work sponsored by an agency of the United States government. 

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constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency 

thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the 

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Evaluation of Two CEDA Weatherization Pilot Implementations of 

an Exterior Insulation and Over-Clad Retrofit Strategy for 

Residential Masonry Buildings in Chicago 

Prepared for:
 

The National Renewable Energy Laboratory
 

On behalf of the U.S. Department of Energy’s Building America Program
 

Office of Energy Efficiency and Renewable Energy
 

15013 Denver West Parkway
 

Golden, CO 80401
 

NREL Contract No. DE-AC36-08GO28308
 

Prepared by:
 

Ken Neuhauser
 

Building Science Corporation
 

30 Forest Street
 

Somerville, MA 02143
 

NREL Technical Monitor: Cheryn Metzger
 

Prepared under Subcontract No. KNDJ-0-40337-02
 

$XJXVW 2013
 

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Contents 

List of Figures ........................................................................................................................................... vii
 

List of Tables .............................................................................................................................................. ix
 

Definitions.................................................................................................................................................... x
 

Executive Summary................................................................................................................................... xi
 

1 Problem Statement............................................................................................................................... 1
 

2 Project Context ..................................................................................................................................... 3
 

2.1 Chicago Masonry Buildings ................................................................................................3
 

2.2 CEDA Weatherization .........................................................................................................3
 

2.3 BSC-CEDA Research Collaboration ...................................................................................5
 

3 Relevance to Building America’s Goals............................................................................................. 6
 

4 Cost Effectiveness ............................................................................................................................... 7
 

4.1 Factors Affecting Cost Effectiveness...................................................................................7
 

4.2 Tradeoffs and Other Benefits...............................................................................................8
 

4.3 Contrast to Interior Insulation Strategies .............................................................................9
 

5 Research Project Description ........................................................................................................... 10
 

5.1 Research Questions............................................................................................................10
 

5.2 Technical Approach...........................................................................................................10
 

5.3 Subject Buildings...............................................................................................................11
 

5.3.1 Two-Family Building.............................................................................................11
 

5.3.2 Larger Multifamily Building..................................................................................12
 

5.4 Data Sources ......................................................................................................................14
 

5.4.1 Field Observation...................................................................................................14
 

5.4.2 Interviews with Contractors...................................................................................14
 

5.4.3 Bids and Other Project Documents........................................................................14
 

5.4.4 Performances Measurement...................................................................................14
 

5.4.5 Simulation Analysis...............................................................................................15
 

6 Over-Clad Retrofit Assembly............................................................................................................. 16
 

7 Assessment......................................................................................................................................... 25
 

7.1 Implementation Observations ............................................................................................25
 

7.1.1 Painted on Air/Water Control ................................................................................25
 

7.1.2 Framing..................................................................................................................28
 

7.1.3 Insulating Sheathing...............................................................................................30
 

7.1.4 Strapping................................................................................................................31
 

7.1.5 Parapet....................................................................................................................33
 

7.1.6 Base of Wall...........................................................................................................37
 

7.1.7 Window Surround..................................................................................................40
 

7.1.8 Cladding and Finish ...............................................................................................49
 

7.2 Cost Analysis .....................................................................................................................54
 

7.3 Performance Assessment ...................................................................................................57
 

7.4 Simulation Analysis...........................................................................................................60
 

7.4.1 Description of Simulation Models.........................................................................60
 

7.4.2 Simulation Results .................................................................................................86
 

8
 Conclusions ........................................................................................................................................ 94
 

8.1 Under what conditions or for which common building situation is the strategy 

recommended? ...................................................................................................................94
 

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8.2 What are the significant challenges to implementation? ...................................................95
 

8.3 What level of airflow control improvement can be expected with the strategy?...............96
 

8.4 What risks inherent in implementation of the strategy must be addressed? ......................97
 

8.4.1 Limited Outward Drying........................................................................................97
 

8.4.2 Foam Plastic Insulation..........................................................................................98
 

8.5 What are the recommended practices critical to achieving performance? ........................99
 

8.5.1 General Recommended Practice............................................................................99
 

8.5.2 Specific Practice Recommendations....................................................................101
 

8.6 What are successful strategies to integrate windows into a masonry wall insulation and
 

cladding retrofit system?..................................................................................................102
 

9 Looking Forward............................................................................................................................... 105
 

9.1 Gaps 105
 

9.1.1 Costs.....................................................................................................................105
 

9.1.2 Aesthetic Coordination ........................................................................................105
 

9.1.3 Assembly Approvals Relative to Fire Safety.......................................................105
 

9.1.4 Product Availability.............................................................................................105
 

9.1.5 Appreciation for Maintenance .............................................................................105
 

9.2 Directions for Further Research.......................................................................................106
 

References............................................................................................................................................... 107
 

Appendix A: Schematic Details Incorporated Into Contractor Bid Packages .................................. 109
 

Appendix B: Insulation and Over-Cladding Work Order for Larger Multifamily Building ............... 112
 

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List of Figures 

Figure 1. Average gas consumption per residential customer for several cold climate states and 

the CEDA territory ................................................................................................................................ 3
 

Figure 2. Two-family over-clad candidate .............................................................................................. 12

Figure 3. (L) North side of larger multifamily over-clad candidate; (R) south side of larger 

multifamily over-clad candidate........................................................................................................ 13

Figure 4. Plan footprint of larger multifamily building showing location of walls receiving the
 

Figure 5. Exterior insulation strategy adopted as the basis for the assembly to be implemented 

insulation and over-clad assembly................................................................................................... 13
 

through the research project............................................................................................................. 17

Figure 6. Schematic retrofit assembly, plan view.................................................................................. 18
 

Figure 7. Schematic retrofit assembly, section view ............................................................................ 19
 

Figure 8. Window sill detail from schematic window details. Note that the water and air control
 

membrane (dashed line at exterior face of brick) returns onto the window frame. .................... 21
 

Figure 9. Window head detail from schematic window details. Note that removing the window trim,
 

trim return, and window return insulation exposes the water and air control membrane

(dashed line at exterior face of brick) of the assembly. ................................................................. 22
 

Figure 10. Window jamb detail from schematic window details. Note that removing the window
 

trim, trim return, and window return insulation exposes the water and air control membrane
 

(dashed line at exterior face of brick) of the assembly. ................................................................. 22
 

Figure 11. Schematic parapet detail. Note the transition membrane that connects the air control 

membrane of the wall (dashed line at exterior face of brick) to the existing roof membrane.... 23
 

Figure 12. Commercially available elastomeric paint used by over-clad contractor......................... 25
 

Figure 13. (L) Elastomeric paint application at larger multifamily building. Note that sills of
 

windows are not painted; (R) Elastomeric paint application at two family building. .................. 25
 

Figure 14. (L) Elastomeric paint application not complete around windows and portions of
 

masonry surface obscured by wood framing; (R) elastomeric paint application at the twofamily building covering the window sill and lapping onto the window frame............................ 26
 

Figure 15. (L) Water and air control layer discontinuous at location of removed electrical conduit
 

(blue circle) and gutter brackets; (R) satellite reception dish and associated cables create 

areas that will require touch-up to establish a continuous control layer with the elastomeric
 

paint ..................................................................................................................................................... 27
 

Figure 16. (L) Window in masonry opening with previously applied sealant; (R) new sealant and 

elastomeric paint applied at window opening. Note persistent gaps at transitions. .................. 27
 

Figure 17. (L) Gap between masonry and lintel; (R) gaps at joints where sealant had not been 

applied as a substrate for the elastomeric paint............................................................................. 28
 

Figure 18. (L) Framing installed in a vertical orientation at 16 in. o.c. as well as horizontally at 8-ft 

increments in the field of the wall. Each window opening is also picture framed with the
 

framing material; (R) Framing installed against masonry at two-family building with horizontal

framing at top of window openings and at 8-ft vertical increments.............................................. 28
 

Figure 19. (L) Framing installed at in a vertical orientation only in the field of the wall. Each 

window opening is picture framed with the framing material. (R) Framing installed against
 

masonry at two-family building with horizontal framing at top of window openings but in a
 

vertical orientation elsewhere........................................................................................................... 29
 

Figure 20. Strapping over insulating sheathing showing switch from 16 in. o.c. to 24 in. o.c. at the
 

two-family building............................................................................................................................. 30
 

Figure 21. (L) Crews installing rigid insulation between furring; (R) second layer of rigid insulation
 

installed over same section of wall as shown at left. Photo taken 11⁄2 hours after photo at left.
 

Finished first floor insulation extends another three window bays to the right of the image. .. 30
 

Figure 22. Offset of seams in successive layers of insulating sheathing. Offset for vertical seam is 

limited by the size of insulation boards and the spacing of framing............................................ 31
 

Figure 23. Wood strapping installed in vertical orientation only over face of insulating sheathing32
 

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Figure 24. (L) Wood strapping with fastener used for attachment through rigid foam insulation to 

2 × 4 framing; (R) longer size fasteners used to attach strapping through thicker rigid foam

insulation layer at parapet................................................................................................................. 32
 

Figure 25. (L) BSC personnel explaining the attachment of trim to vertically oriented strapping; 

(R) the same window after the contractor reconfigured the strapping......................................... 33

Figure 26. Beveled roof insulation used to true new cladding attachment at top of wall. Note that
 

Figure 27. (L) Contractors mock up of frame over parapet using 2 × 12 attached to vertical furring 

fasteners are left loose at the time of this photo. ........................................................................... 34
 

attached to face of wall; (R) OSB attached to 2 × 12 at inside face of parapet............................ 35
 

Figure 28. Schematic alternate parapet detail providing a frame over the top of the parapet. Note
 

the transition membrane that connects the air control membrane of the wall (dashed line at

exterior face of brick) to the existing roof membrane. ................................................................... 35
 

Figure 29. Finished parapet cover at two-family building .................................................................... 36
 

Figure 30. (L) Transition membrane not connected to elastomeric coating at face of wall; (R)
 

transition membrane not adhered to roof membrane at inside face of parapet .......................... 36
 

Figure 31. Schematic detail for base of insulation and over-clad assembly...................................... 37

Figure 32. Base of wall with constricted access for attachment of screening................................... 38
 

Figure 33. Base of wall insulation and over-clad assembly very close to grade at the two-family 

building................................................................................................................................................ 39
 

Figure 34. Excerpt of revised detail for protection at base of wall insulation and over-clad
 

Figure 36. (L) Window set directly in masonry opening at the larger building; (R) windows set in 

assembly ............................................................................................................................................. 40
 

Figure 35. Perforated soffit material use for protection at base of insulation and over-clad
 

assembly ............................................................................................................................................. 40
 

metal-clad trim/frame surround at the two-family building............................................................ 41
 

Figure 37. Return trim at the larger building butting into the vinyl window frame ............................ 42
 

Figure 38. Return trim at the smaller building butting into the metal-clad trim surround (blue
 

arrows) leaving the joint around the vinyl window frame exposed (red arrow) .......................... 42

Figure 39. (L) Contractor mockup of window surround; (R) BSC personnel explaining placement of
 

flashing membrane............................................................................................................................. 43
 

Figure 40. Window sill detail from schematic window details. Note that removing the window sill
 

trim and window sill insulation exposes the water and air control membrane (dashed line at
 

exterior face of brick) of the assembly............................................................................................. 44

Figure 41. Second mockup of window surround showing the flashing membrane placed beneath 

the insulation return........................................................................................................................... 44
 

Figure 42. (L) Insulation return at the jamb installed before the insulation return at the sill. Note
 

also that the sill flashing membrane does not extend over the outer face of the insulating 

sheathing. This was later corrected. (R) Sill trim installed after the jamb return trim. Sill
 

extensions are actually cut around the jamb trim. Note that the window sill trim has a kick-out

to direct water away from the face of the building.......................................................................... 45
 

Figure 43. Revised detail for window sill treatment .............................................................................. 46
 

Figure 44. Revised detail for the window surround at the jamb .......................................................... 47
 

Figure 45. (L) Window head return trim sloping toward the window; (R) CEDA personnel
 

demonstrating the reconfiguration of the window head return trim............................................. 48
 

Figure 46. (L) Window head casing with no drip cap and sealant gaps; (R) Contractor project

manager reviewing the drip cap flashing with the crew................................................................. 48
 

Figure 47. Window head return trim with profile channeling water to weep holes at the front edge49
 

Figure 48. Finished side of the larger building ...................................................................................... 50
 

Figure 49. Treated wall at the smaller building striking a contrast with the untreated wall at the
 

rear of the building ............................................................................................................................. 50
 

Figure 50. (L) Fiber cement panels back-primed prior to installation; (R) Progression of panel

installation and face-priming at the second treated side of the larger building.......................... 51
 

Figure 51. Caulked butt joints between 4 × 8 panels............................................................................. 52
 

Figure 52. Butt joints between the panels visible in the finished wall ................................................ 52
 

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Figure 53. Visible butt joints in the finished wall................................................................................... 53
 

Figure 54. (L) Fiber cement lapped siding with fasteners at the top edge concealed by lap of

subsequent piece; (R) fasteners for the panel cladding system exposed ................................... 53
 

Figure 55. Predicted heating and cooling energy end uses for the two-family building................... 87
 

Figure 56. Predicted heating and cooling energy end use for the larger multifamily building ........ 88
 

Figure 57. Predicted heating and cooling energy end use for the larger multifamily building 

without accounting for air leakage reduction.................................................................................. 89
 

Figure 59. Predicted annualized energy-related costs and source energy savings for the larger 

Figure 60. Predicted annualized energy-related costs and source energy savings for the twoFigure 61. Predicted annualized energy-related costs and source energy savings for the larger 

Figure 58. Predicted annualized energy-related costs and source energy savings for the twofamily building under four upgrade scenarios................................................................................ 90
 

multifamily building under four upgrade scenarios ....................................................................... 90
 

family building under four upgrade scenarios using net energy-related measure costs........... 92
 

multifamily building under four upgrade scenarios using net energy-related measure costs.. 92
 

Figure 62. Screening at the base of the wall that fails to protect the exposed edge of the insulating 

sheathing near grade ....................................................................................................................... 100
 

Unless otherwise noted, all figures were created by BSC. 

List of Tables 

Table 1. Height and Access Impact on Insulation and Over-Cladding Costs..................................... 54
 

Table 2. Nonenergy Benefit Comparison................................................................................................ 56
 

Table 3. BEopt Modeling Inputs for Two-Family Building .................................................................... 62
 

Table 4. BEopt Modeling Inputs for Larger Multifamily Building......................................................... 64
 

Unless otherwise noted, all tables were created by BSC. 

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Definitions 

ACH50	 Building air changes per hour induced by a relative pressure 

difference of 50 Pascals between the building and ambient 

conditions 

BSC	 Building Science Corporation 

CEDA	 Community and Economic Development Association of Cook 

County, Incorporated 

CEDA Wx	 CEDA Weatherization, a division of CEDA 

cfm50	 Airflow, usually through an enclosure or assembly induced by 

a relative pressure difference of 50 Pascals 

CMU	 Concrete masonry unit 

DOE	 U.S. Department of Energy 

EIFS	 Exterior insulation and finish system 

ft2	 Square foot, square feet 

IHWAP	 Illinois Home Weatherization Assistance Program 

OSB	 Oriented strand board 

PVC	 polyvinyl chloride 

R-value	 Insulation value of walls and roofs 

SERC	 Sustainable Energy Resources for Consumers, an innovation 

grant program of the U.S. Department of Energy 

U factor	 Insulation value of windows 

Wx	 Weatherization 

XPS	 Extruded polystyrene 

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Executive Summary 

This project examines the implementation of an exterior insulation and over-clad strategy for 

brick masonry buildings in Chicago. The strategy was implemented at a free-standing, two-story, 

two-family dwelling and a larger free-standing multifamily building. The test homes selected for 

this research represent predominant housing types for the Chicago area. High heating energy use 

typical in these buildings threatens housing affordability. Uninsulated mass masonry wall 

assemblies also have a strongly detrimental impact on comfort. It will be necessary to 

significantly change the performance of the wall if these masonry buildings are to be elevated to 

a level of performance on par with current standards. 

Significant changes to the performance of masonry wall assemblies is generally beyond the reach 

of typical weatherization (Wx) program resources. Community and Economic Development 

Association of Cook County, Incorporated (CEDA) has secured a Sustainable Energy Resources 

for Consumers (SERC) innovation grant sponsored by the U.S. Department of Energy (DOE). 

This grant provides CEDA the opportunity to pursue a pilot implementation of innovative 

approaches to retrofit in masonry wall enclosures. This research project evaluates the 

implementation of an exterior insulation and over-cladding approach at two masonry buildings 

representing predominant types within the Chicago-area housing stock. The retrofit measures are 

evaluated in terms of feasibility, cost, and performance. 

The exterior insulation and over-clad strategy was designed to allow implementation by 

contractors active in CEDA Wx programs and using materials and methods familiar to these 

contractors. 

The research identifies: 

•	 Conditions under which exterior insulation and over-clad of masonry walls is
 

recommended
 

•	 Significant implementation challenges to exterior insulation and over-clad of masonry 

walls 

•	 Levels of airflow control that can be achieved with the strategy 

•	 Risks inherent in the approach that must be addressed 

•	 Measures and practices critical to achieving performance in exterior insulation and overclad of masonry walls 

•	 Successful strategies to integrate windows into masonry wall exterior insulation and 

over-cladding systems. 

Through observations of the strategies implemented, the research described in this report 

identifies measures critical to performance as well as conditions for wider adoption. The research 

also identifies common factors that must be considered in determining whether the exterior 

insulation and over-clad strategy is appropriate for the building. 

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1 Problem Statement 

The predominant construction types for residential structures—single-family detached as well as 

multifamily—in Chicago involve load-bearing masonry walls. Methods to insulate these wall 

assemblies are typically beyond the reach of Wx programs. Yet, the need for improved thermal 

performance in these masonry buildings is clear. Residential buildings in the Chicago area 

exhibit appreciably higher heating energy use than other types of construction and other cold 

climate regions of the country (AGA 2010). Energy costs are an increasing burden on household 

incomes. Uninsulated mass masonry wall assemblies with poor performing glazing also have a 

strongly detrimental impact on thermal comfort. It will be necessary to significantly change the 

performance of the wall thermal enclosure if these masonry buildings are to be elevated to a level 

of performance on par with minimum current code standards. 

Adding insulation to the walls of such masonry buildings in cold, and particularly cold and wet, 

climates may cause performance and durability problems in some cases. The problems and 

solutions are outlined by practitioners such as Maurenbrecher et al. (1998), Gonçalves (2003), 

and Straube and Schumacher (2002, 2004). 

Examples of concerns associated with interior insulation of mass masonry walls include freezethaw damage—due to reduced outward heat flow—and the decay of wood structural framing 

members (typically floor joists) that are embedded in mass assemblies—due to increased 

equilibrium moisture contents. The masonry freeze-thaw issue has been examined by (among 

others) Mensinga et al. (2010) and Straube et al. (2012). The embedded floor joist decay issue 

has been studied by some practitioners (Dumont et al. 2005; Morelli 2010; Ueno 2012), but 

many issues remain unresolved. 

In addition to the risks associated with interior insulation of mass masonry, this strategy has 

limitations to performance in factors such as the common occurrence of integrated floor or wall 

assemblies representing thermal bridges. The amount of insulation that can be accommodated to 

the interior of a mass masonry wall without reconfiguring the interior space is typically limited 

to the depth of interior framing or strapping cavities and the performance of insulation materials 

that can be loose blown into these cavities. 

When a building is occupied, the application of interior insulation strategies can be very 

disruptive to residents. Working around resident schedules and belongings also tends to 

significantly complicate the implementation. 

Adding insulation to the exteriors of existing buildings has been demonstrated to be an effective 

means to overcome these limitations and provide higher effective R-values for building wall 

assemblies. The benefits of this approach extend beyond just added thermal resistance; benefits 

of increased building durability and airtightness are often also realized (Ueno 2010). 

The underlying concept of insulating the exterior of existing masonry walls has a variety of 

advantages for durability and air barrier continuity (Hutcheon 1964; Lstiburek 2007). 

Furthermore, exterior insulation retrofit can often achieve a greater amount of thermal resistance 

than is typically feasible with interior insulation retrofit. The practice should be simple; however, 

several problems stand in the way of widespread implementation. For example, manufacturers of 

cladding systems and exterior insulation materials often limit thicknesses to 11⁄2 in. with their 

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warranties; the cladding attachment is therefore an issue. This problem has been tackled by 

various researchers and practitioners (Straube and Smegal 2009; Pettit 2009; Joyce 2009; Ueno 

2010; Baker 2012). Demonstrations by members of our research team have shown that up to 

8 in. of exterior insulation over the exteriors of masonry and frame buildings is practical 

(Lstiburek 2009). 

The lack of widespread recognition of attachment methods by manufacturers has resulted in 

obstacles for building official and building code acceptance. Additionally, the construction 

industry has not demonstrated familiarity with details for water management and integration of 

window systems, door systems, decks, balconies, and roof-wall intersections in assemblies with 

thick exterior insulation. Baker (2012) proposed an engineering basis and support for the 

installation of thick layers of exterior insulation on existing masonry and frame walls. His report 

also demonstrates water management details necessary to integrate windows, doors, decks, 

balconies, and roofs. 

Long-term solutions to the energy cost burden and comfort problems of existing masonry 

construction buildings will require measures to improve the performance of the masonry wall 

assemblies. Widespread adoption of one possible solution, exterior insulation of masonry walls, 

will require demonstration projects that prove the feasibility of the techniques and evaluate 

challenges. Through the SERC innovation grant, CEDA has the opportunity to demonstrate and 

study such measures. Through a Building America partnership, Building Science Corporation 

(BSC) has partnered with CEDA to provide technical guidance for—and evaluation of—the 

retrofit measures implementation. In providing technical guidance toward water management 

details and cladding attachment, BSC drew on previous and concurrent research into exterior 

insulation retrofits. 

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2 Project Context 

2.1 Chicago Masonry Buildings 

Masonry buildings are the dominant residential building type in Chicago. While this may be 

expected for large older multifamily buildings, it is also true of smaller residential buildings in 

Chicago. According to Cook County Assessment Department data, 57% of one-unit housing 

stock and 58% of two- to four-unit housing stock in Cook County is of masonry construction.1 

Compilation of utility data shows Illinois has the second-highest average gas consumption per 

residential customer for all the United States (AGA 2010). Only residential gas customers in 

Alaska use more, on average, than residential gas customers in Illinois (see Figure 1). Homes 

within the CEDA service territory are using even more on average than the rest of the state, 

surpassing the residential customer average for Alaska and using nearly twice the gas per 

household as other heating climate areas such as Minnesota. 

Figure 1. Average gas consumption per residential customer for several 

cold climate states and the CEDA territory 

2.2 CEDA Weatherization 

The Multifamily portion of the Illinois Home Weatherization Assistance Program (IHWAP) is 

for building owners who provide housing to income-eligible residents in Chicago and suburban 

Cook County. The program is at no cost to the building owner, if 66% or more of the tenants are 

income eligible. 

1 Percentages reported are based on 2010 data. 

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The CEDA Wx program serves income-eligible clients and includes households residing in 

multifamily buildings, in Cook County, Illinois. A multifamily building qualifies for services if 

at least two thirds of the households in a multifamily building are income eligible. 

CEDA Wx is one of more than 30 community action agencies that participate in IHWAP. The 

Illinois Department of Commerce and Economic Opportunity administers the program; its Office 

of Energy Assistance monitors all agencies in the IHWAP network. 

The services that CEDA Wx provides are structured around a comprehensive energy audit 

performed by a CEDA Wx assessor. The audit leads to development of a work order that may 

comprise measures in the following categories:2 

•	 Retrofit measures: insulation, compact fluorescent lamps, refrigerator replacement, lowflow shower heads and faucet aerators, heating system replacement, window and door 

replacement 

•	 Air sealing measures 

•	 Health and safety measures (limited to $600 per unit): handrails, fire extinguishers, 

gutters, downspouts, and decommissioning of unvented space heaters 

•	 Incidental repair measure (limited to $500 per unit). 

DOE Wx program funding requires that the entire building or house receive a savings-toinvestment ratio of 1 or greater before it can be weatherized.3 Software tools are used to estimate 

the savings from various measures. Costs per work item are sent to bid by approved contractors. 

The state-level administration of IHWAP sets a limit of $5,200 to the expenditure for each 

eligible unit. Approved contractors participating in the CEDA Wx programs implement the work 

scope. Upon completion of the work, CEDA Wx assessors conduct inspection of the work. 

CEDA weatherizes all types of single-family and multifamily structures. In typical years, CEDA 

Wx has weatherized 3,000–4,000 housing units. Units in multifamily buildings typically account 

for 10%–30% of the total number of housing units served. With funding made available through 

the American Recovery and Reinvestment Act, the budgeted volume of units has increased to a 

total of 7,500 units in 2010, 11,000 units in 2011, and 9,000 units in 2012. 

Because the regular program limits are the same for each stand-alone single-family house as for 

a unit in a multifamily building, the program resources relative to enclosure area and per building 

tends to be significantly higher for multifamily buildings participating in the programs. This has 

allowed for measures such as replacing windows with high performance windows to be 

implemented through the Wx program in multifamily buildings. However, the Wx program has 

not been able to implement measures to address the masonry-bearing walls. 

The high proportion of masonry buildings within the CEDA service territory creates a persistent 

challenge for CEDA Wx programs. An analysis of the programs found that energy use 

reductions achieved by Wx activity in homes of masonry construction are typically one third less 

than what is achieved in wood-framed homes. It is certainly conceivable that this reflects the 

2 Note that the list of allowable measures in the program has changed slightly since the period of research. 3 Typically, the value of savings is taken as the present value of recurring savings for a period of time at a standard 

discount rate. The present value of savings is then compared to the initial cost or investment of the measure. 

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thermal performance of masonry wall assemblies and the lack of opportunity for improvement at 

levels of investment commensurate with typical Wx programs. The furring cavity between the 

brick wall and the interior finish does not provide adequate space for effective insulation. The 

program has not pursued measures based on interior wall build-out for insulation due to 

anticipated costs and complications. Neither has insulation and recladding at the exterior been 

incorporated into available measures. Such strategies have been generally regarded as too 

unfamiliar to the contractor base and as potentially representing fire safety concerns. 

In 2011, CEDA was awarded special grant funding through the SERC program, an innovation 

grant program of DOE. This grant allowed CEDA to apply resources beyond regular Wx 

program allocations at a limited number of selected projects. The grant allowed the budget for a 

single-family unit to increase by $9,600 and for multifamily unit by $6,400. 

The SERC innovation grant has provided CEDA the opportunity to pursue limited 

implementation of various strategies to address building performance weaknesses that have 

heretofore been out of reach of the Wx programs. One of the innovations that CEDA opted to 

pursue with this funding is exterior insulation and cladding of masonry walls. 

2.3 BSC-CEDA Research Collaboration 

In 2010 CEDA and BSC gathered CEDA Wx personnel, management, and selected consultants 

to envision a path toward significantly increasing performance of homes treated through CEDA 

programs and, in particular, masonry buildings. These meetings identified major packages of 

measures to be researched through prototype and/or pilot implementations. Taken together, the 

major packages describe a comprehensive high performance retrofit. The first package that the 

collaboration evaluated through a series of implementations was an advanced Wx approach for 

the roof of 11⁄2-story brick bungalow homes (see Neuhauser 2012). 

The SERC grant provided a potential opportunity for the BSC-CEDA collaboration to evaluate 

another major package for masonry buildings: insulating and over-cladding of masonry walls. 

BSC and CEDA began the preliminary work of developing schematic details for the over-clad 

assembly and evaluating a number of potential building candidates. 

After BSC and CEDA began this preliminary work, two factors emerged that resulted in 

disruptions to the collaborative effort. On the one hand, management changes within the CEDA 

organization resulted in uncertain support for the project. On the other hand, the wider national 

political climate created some uncertainty as to whether BSC would be able to support its 

involvement in the project. As a result, funding and implementation of the exterior insulation and 

over-cladding project were uncertain during significant portions of the originally projected 

project timeline. This affected BSC’s ability to participate in the project. In fact, BSC’s 

participation was essentially suspended for a period from prior to contractor bidding until just 

prior to the start of construction. As a result, critical windows of opportunity to provide guidance 

to contractors and to obtain pre-retrofit performance data were missed. The availability of CEDA 

resources was also constrained during the project. This hampered collection of certain postretrofit performance data. 

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3 Relevance to Building America’s Goals 

The energy performance goal of the DOE Building America program is to reduce home energy 

use by 30%–50% compared to 2009 energy codes for new homes and pre-retrofit energy use for 

existing homes. For CEDA such reductions in existing homes are imperative to maintaining 

housing affordability and quality of life for CEDA’s constituents. It is clear that uninsulated 

masonry walls are a significant source of heat loss in any heating-dominated climate. Long-term 

housing affordability and comfort will require retrofits of these assemblies. 

The use of exterior insulation on wall assemblies is an effective means to provide additional 

thermal resistance to enclosure assemblies. The exterior insulation approach is particularly well 

suited to retrofit projects, as it minimizes disruption to the interior and does not detract from 

usable floor area. Exterior insulation retrofit strategies present the possibility to far exceed 

current code levels of performance for new exterior walls. 

The specific target of the measures implemented through this research and the dominant target of 

CEDA Wx programs generally is to reduce energy costs and improve comfort in a heatingdominated climate. Demonstrating an effective masonry retrofit strategy will support wider 

adoption of an approach with great potential. This potential is remarkable both in terms of the 

level of benefits to individual treated buildings and residents of these buildings as well as in 

terms of the number of buildings to which the strategy is applicable. The measures demonstrated 

and evaluated in this research task are complementary to measures demonstrated and evaluated 

through Neuhauser (2012). The measures demonstrated and evaluated in that research task as 

well as those evaluated in the current research task constitute components to comprehensive 

masonry building retrofit. 

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4 Cost Effectiveness 

4.1 Factors Affecting Cost Effectiveness 

There exist at least three somewhat inherent challenges to assessing the cost effectiveness of the 

type of exterior insulation retrofit evaluated in this report. First, the cost of adding layers of 

insulation to the exterior of the building is extremely front loaded. That is, the major costs 

associated with adding thick layers of insulation are incurred with the first layer of insulation 

added. Second, the front-loaded costs of insulation are inextricably linked to nonenergy benefits. 

And third, conditions of access to the building represent a significant cost determinant for the 

approach and would cause the cost to vary widely between buildings. 

Most of the cost of an exterior insulation retrofit is represented in the attachment system and 

cladding needed with the first layer of exterior insulation. Typically, methods of insulating 

assemblies face diminishing returns as thermal resistance is increased. Cost effectiveness—in 

terms of incremental energy savings relative to incremental cost—of additional insulation would 

depend upon the incremental cost decreasing more than the energy savings diminishing.

4 In the 

case of exterior insulation and over-clad of masonry structures, subsequent layers or thicknesses 

of insulation added to the system entail a much lower cost than the initial level of thermal 

resistance represented by the base system. Because of the high relative cost of the initial level of 

insulation and the diminishing costs for subsequent layers, cost effectiveness relative to energy 

savings is likely to improve as insulation is added after the initial layer of insulation. 

The measures necessary to allow installation of the first layer of insulation in the exterior 

insulation and over-clad approach are also responsible for important nonenergy benefits of the 

approach (see Section 4.2). Therefore, it would be logical to assign a portion of the costs for this 

layer to nonenergy benefits, leaving less than the full cost of this layer assigned to the energy 

benefits. Such apportioning of costs among benefits has a profound effect on perceptions and 

measures of cost effectiveness relative to energy savings or other benefits. 

Both the working area at the base of a building and the height of the building will have a 

significant impact on the ultimate cost to provide exterior insulation and over-clad. In terms of 

height, the inflection point in cost is above two stories in height. Occupational safety regulations 

permit access by ladder for work on structures up to two stories in height. Above this height, 

staging or a lift mechanism would be required, thus significantly increasing the cost of the job 

and the resulting unit cost for the measure. The contractors involved in this research project 

indicate that a mechanical lift operating from the ground is the least costly and most flexible 

means to perform exterior building enclosure work above two stories. Use of such a lift, 

however, would require a relatively large area of clear and level ground adjacent to the building. 

Such access is not unheard of in urban environments, but also, certainly cannot be expected as a 

typical condition. When there is not sufficient space for operation of a mechanical lift on the 

ground adjacent to the building, pipe staging or, where the building can support it, swing staging 

would be required. These represent significant additional cost and labor time burdens relative to 

a mechanical lift. Even below two stories, working access is a significant factor in the unit cost 

4 Cost effectiveness expressed this way is sometimes an overly simplistic metric. There are other rationales, such an 

energy cost risk management and energy performance differential over the life of the measure that may be used in 

identifying appropriate levels of insulation. 

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of the measure, as space between adjacent buildings may not be sufficient to allow the use of 

ladders. In fact, the development pattern for most of the territory that is served by CEDA Wx has 

narrow spacing along the sides between adjacent one- and two-family buildings. The contractors 

performing work in this research project generally regarded the ground-level access as more 

important than building height as a factor in overall project cost. 

4.2 Tradeoffs and Other Benefits 

Improved durability, water management, and comfort are nonenergy benefits expected from the 

implementation of the measures outlined in this report. Other potential nonenergy benefits 

include reduced maintenance and improved aesthetics. This research task will not attempt to 

quantify the value of these nonenergy benefits, although it does seek to document them. 

Using exterior insulation has many additional benefits other than simply increased thermal 

resistance. In masonry building assemblies, the potential for freeze-thaw is practically 

eliminated, since this approach not only keeps the masonry warmer, but also addresses the 

exterior rainwater absorption into the masonry (which is the leading moisture source related to 

freeze-thaw damage to buildings). Another benefit is the increased condensation resistance that 

this strategy provides for cold climate buildings. 

In addition to keeping the structure to the inside of the thermal control layer and thereby 

avoiding the risks of freeze-thaw damage associated with placing the masonry structure to the 

outside of the thermal control layer, the strategy employed in this research provides a platform 

for superior water management. The approach evaluated in this research uses a continuous water 

control layer that is applied over the face of the brick masonry and integrated with new or 

existing flashings to direct water out to a drainage cavity or over the surface of the cladding. The 

use of furring strips for cladding attachment over thick exterior insulation also creates a drainage 

cavity that allows water penetrating through the new cladding layer to quickly drain out of the 

system. The fact that the furring strips are an intrinsic component of this system provides a 

significant added benefit to the long-term durability of these wall assemblies. 

A fundamental benefit of insulating uninsulated masonry walls is thermal comfort improvements 

resulting from radiant surface temperature effects. The techniques used in this insulation and 

over-cladding strategy are also expected to result in air leakage reduction. Air leakage reductions 

would result in energy savings and could also benefit comfort, indoor air quality, and building 

durability. 

The application of an insulation and cladding assembly over an existing masonry wall could also 

result in reduced maintenance expenses and improved aesthetics. Reduced maintenance expenses 

would result where the building owner regularly maintained the masonry wall such as by 

periodically repointing the brick. The owner of one of the buildings that is the subject of this 

research reports hiring a contractor to perform repointing on a portion of the building every year. 

Other building owners might be performing little to no maintenance on the masonry and, 

therefore, would not see savings from reducing maintenance needs.5 

The improvement in aesthetics is, admittedly, a subjective assessment. Pertinent to the 

assessment, however, is the condition of the existing masonry over which this insulation and 

5 The building would certainly benefit in terms of longevity of the masonry. This may not be a concern for all 

building owners, however. 

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over-cladding strategy would be applied. The side and rear walls of residential masonry 

buildings in Chicago are typically found to be of lower quality masonry than the street-facing 

elevations. Side and rear walls typically have mortar joints that are not struck and brick that is of 

visibly lesser quality and of inconsistent colors. 

4.3 Contrast to Interior Insulation Strategies 

In contrast to exterior insulation, insulation to the interior of existing masonry walls does not 

provide comparable benefits to building durability and water management. Insulation to the 

interior of the building structure will also make that structure colder (in heating seasons) thereby 

increasing the potential for condensation in the assembly, freeze-thaw damage to the masonry, 

and moisture degradation to embedded framing members. While insulation to the interior of 

masonry walls does not necessarily portend certain disaster regarding these damage functions, 

risks need to be carefully assessed for each circumstance. Therefore, it is not possible to propose 

a uniform approach for widespread application. 

Interior insulation does not offer the opportunity to improve exterior aesthetics or reduce 

maintenance requirements for the exterior masonry. On the other hand, it is very common that 

the street elevation of Chicago masonry buildings exhibit detailing and quality of work that has a 

definite aesthetic value to the building. Exterior insulation and over-cladding of these street 

façades would not be desirable. 

Relative to what can be achieved with exterior insulation, it is challenging to achieve similar 

levels of thermal performance with insulation applied to the interior of existing masonry walls. 

Interior insulation strategies will either reduce usable floor area or be limited by the depth of 

framing or furring cavities. Even where nominal thermal resistance in the field of the wall is 

comparable, interior insulation of mass masonry has greater limitations to effective performance 

due to the common occurrence of thermal bridges such as integrated floor or wall assemblies. 

Interior insulation may be readily accommodated in interior renovation activities involving 

removal or significant replacement of interior finishes along the exterior wall. If significant 

removal of interior finishes is not planned, interior insulation will typically require appreciable 

repair to exterior wall finishes. Thus, interior insulation approaches represent significant 

disruption to the use of the interior. A very significant constraint to interior insulation that will 

apply to virtually all buildings in active use is that interior insulation strategies are not easily 

compatible with an occupied retrofit. 

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5 Research Project Description 

This research project leverages targeted grant funding obtained by CEDA to implement a 

strategy to address the thermal losses and comfort detriment inherent in the masonry bearing wall 

construction, the predominant wall assembly for residential buildings in the Chicago area. It is 

understood that addressing these losses and comfort impacts is important to the long-term 

viability of this housing stock. It is not known, however, whether the retrofit packages 

demonstrated in these buildings will be able to be delivered through Wx program channels 

outside of special grant funding. 

5.1 Research Questions 

The research project evaluates a masonry wall retrofit approach involving exterior insulation and 

over-cladding. The research project is aimed at answering the following questions pertinent to 

wider implementation of the approach: 

•	 Under what conditions or for which common building situation is the strategy
 

recommended?
 

•	 What are the most significant challenges to implementation? 

•	 What level of airflow control improvement can be expected with the strategy? 

•	 What risks inherent in the strategy must be addressed in the implementation of the
 

strategy?
 

•	 What are the recommended practices critical to achieving performance? 

•	 What are successful strategies to integrate windows into a masonry wall insulation and 

cladding retrofit system? 

Answers to these questions will help researchers, developers, contractors, and designers to 

evaluate the application of these strategies both within the Chicago area as well as elsewhere. 

5.2 Technical Approach 

The research activities include the following: 

•	 Conduct in-field assessments of prospective retrofit community homes/buildings to 

identify both unique and common characteristics of building construction. 

•	 Develop schematic details for insulation and over-clad systems and for integration of 

windows with the system. 

•	 Conduct prework measurement of air leakage and building conditions. 

•	 Review contractor bids and shop drawings, revise assemblies and details as necessary. 

•	 Perform oversight and observation of contractor implementation of measures. 

•	 Conduct postwork air leakage measurement and monitoring of conditions within parts of 

buildings affected by measures. 

•	 Analyze cost and performance data. 

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CEDA Wx program assessors and Multifamily Program staff mined the CEDA Wx database of 

eligible customers to identify likely homes and buildings to participate in the research effort. 

Criteria used in this initial screening included willingness and interest of the building owner, 

building height of three or fewer stories, solid masonry bearing wall construction, uninsulated 

wall assembly, masonry in reasonably good condition without major repointing required, 

reasonable access to roof-wall intersection, and full eligibility for regular program incentives. 

Assessors then visited the homes and buildings to document conditions and obtain measurements 

of pertinent building geometries. 

Following preliminary selection of a set of candidate buildings, BSC developed schematic 

assembly drawings and details for both the general and unique conditions identified. The 

research team was able to provide oversight of the measure implementation at each of two 

buildings involved in the research. 

Some planned research activities were not carried out due to funding uncertainty and 

unanticipated resource constraints. In the initial plan for this research, BSC was to review work 

scopes prepared by CEDA prior to bidding by the implementing contractor. The research 

partnership had earlier envisioned that BSC would be present during bidding conferences or 

other meetings with prospective contractors to explain the strategy and answer questions. As 

discussed in Section 2, BSC participation was suspended during the bid process and up until the 

start of construction. As a result, BSC did not have an opportunity to review contractor bids or 

shop drawings (there do not appear to have been any of the latter). BSC did prepare revised 

details in response to observations made during site visits at the early stage of construction. 

Obtaining useful pre-retrofit air leakage measurements of the larger building involved in the 

study proved infeasible due to the conditions of occupancy and the size of the building. CEDA 

personnel were able to perform air leakage testing at the smaller of the two buildings involved in 

the study. 

5.3 Subject Buildings

The two buildings selected to participate in this research include a two-story, two-family 

building and a larger multifamily building containing 80 single-room occupancy units. The 

larger multifamily building features three occupied floors over a basement that contains some 

meeting and office spaces associated with the operation of the facility. 

5.3.1 Two-Family Building 

Although it is a multifamily building, the two-family building represents many characteristics 

typical of single-family homes. These typical characteristics include the project scale, the 

spacing between buildings, and a more finely articulated street façade (Figure 2). A very 

common feature of detached single-family masonry homes that is not represented in this subject 

building is an intersection between an exterior wall and a roof overhang. Instead the subject 

building has a low-sloped roof with a parapet at the intersection of the treated wall and roof. This 

configuration is not uncommon. It required a connection from the wall system, over the parapet 

to the roof. Subsequent to launching construction on this building, it was found to have another 

feature apparently common in low-sloped buildings of similar age in the area: a parapet in 

significant disrepair. 

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The inclusion of two qualifying dwelling units within the building allowed a larger budget for 

the enclosure retrofit than would be possible with a single-family home. 

Figure 2. Two-family over-clad candidate 

(Credit: Scott Sanders, CEDA) 

Because of the limited space between buildings, pipe staging (scaffolding) was required for 

working access to the building. For one side of the building, even the narrow staging used 

(extending approximately 5 ft from the building) was feasible only because the same owner 

owned both properties to either side of a small alleyway. 

Windows on this building had been replaced with double-glazed, low-e, vinyl-framed windows 

through a different low-income Wx program prior to CEDA involvement. The available budget 

for this project did not permit removal and reinstallation of these windows. 

Because of the significant aesthetic value of the brickwork at the front of the building, the front 

section was not included in the insulation and over-clad project. The rear of the building was also 

excluded because of an attached fire escape. The relocation or reconstruction of this fire escape, 

as would have been required, was beyond the budget of the project. 

5.3.2 Larger Multifamily Building 

The larger building included in this project provided the scale representing many urban 

multifamily buildings. It required staging or lifts such as would be required for buildings more 

than two stories in height. For this pilot implementation, portions of two sides of the building 

were designated to receive the insulation and over-clad assembly (Figure 3 and Figure 4). The 

reasons for designating portions of the wall rather than the entire wall include the constraint of 

available budget for this work, reasonable access (a portion of the north-facing wall is less than 1 

ft from an adjacent building) and preference of the building owner to allow CEDA to implement 

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an “experimental” exterior treatment to less visible portions of the building. These designated 

portions of the wall provided ample area to evaluate a large-scale implementation of the exterior 

insulation and over-cladding strategy. 

Figure 3. (L) North side of larger multifamily over-clad candidate; 

(R) south side of larger multifamily over-clad candidate 

(Credit: Scott Sanders, CEDA) 

Figure 4. Plan footprint of larger multifamily building showing location of walls receiving the 

insulation and over-clad assembly 

(Credit: CEDA) 

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Because of the access constraints, work on both designated sides of the building required the use 

of a suspended staging. 

Windows on this building had been recently replaced with high performance vinyl-framed 

windows through a CEDA Wx program. The windows were designated to remain in place. 

5.4 Data Sources 

The information used in the evaluation of the measures derives from field observation, 

interviews with implementing contractors and crews, project documents, performance 

measurements, and simulation analysis. 

5.4.1 Field Observation 

Both during early stages of implementation at the larger building and throughout the 

implementation at the smaller two-family building, CEDA Wx personnel made regular and 

frequent visits to the job site. CEDA Wx personnel took photos during visits and rapidly 

conveyed these photos (sometimes before leaving the jobsite) to BSC for review. Upon a joint 

review of the photos and discussion of job site issues, CEDA Wx and BSC would develop 

directions to convey to the contractors as well as areas to investigate in subsequent field visits. 

BSC personnel visited the project sites with CEDA Wx personnel during the candidate building 

selection phase as well as during implementation of measures. These visits proved valuable for 

understanding site conditions and observing apparent challenges. 

5.4.2 Interviews with Contractors 

Onsite review of the implementations also presented opportunities to gain candid assessments 

from the contractors and crews. This provided useful insights into challenges encountered. 

Meetings were also scheduled with contractors after significant completion of the work to 

provide an opportunity for the contractors to provide feedback and for the research team to ask 

questions of the contractors. Follow-up telephone and electronic communications with 

contractors also provided useful information. 

5.4.3 Bids and Other Project Documents

Contractor bids provide a basis for determining measure costs. Submittals provided by 

contractors with each bid indicate specific products included in the materials costs. Work orders 

prepared by CEDA provide additional information about the cost of measures and scope of work. 

As change orders were not allowed on this project, the bids of the contractors implementing the 

work reflect the cost paid for the work. 

5.4.4 Performances Measurement 

For the smaller building, pre- and post-retrofit air leakage measurements are used to derive a 

cfm50 measurement for the building. These measurements are then normalized to enclosure area 

and treated wall area. There are some problems with this methodology for assessing the air 

leakage reduction attributable to this strategy. First, the air leakage measurement changes also 

reflect work other than that associated with the insulation and over-cladding measure. Also, 

because of likely airflow pathways within and between wall assemblies, the results from treating 

portions of the wall do not necessarily extrapolate to the case of treating all nonstreet elevations 

of the building. 

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For the larger building, pre-retrofit air leakage measurements were conducted within individual 

residential apartments. It was not possible to conduct guarded leakage tests for individual 

apartments. Given the suspected presence of overriding interunit leakage that obscures changes 

in leakage through exterior walls, the team did not pursue post-retrofit air leakage testing in this 

building. 

Given the timeframe for the research and that of measures implementation, it was not possible to 

obtain energy consumption data reflecting heating season conditions after implementation of the 

measures. 

5.4.5 Simulation Analysis 

Simulation analysis using BEopt is employed to project the impact of the retrofit measures on 

heating energy usage. The simulation analysis reflects an idealized case where the whole exterior 

wall assembly can be treated to the same level of thermal performance. While this results from a 

limitation of the simulation tool, it also represents a comprehensive retrofit scenario where the 

exterior insulation and over-cladding treatment is paired with a different but complementary 

treatment for the street elevation. 

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6 Over-Clad Retrofit Assembly 

Basic parameters of the insulation assembly were identified during initial discussions between 

the research partners about joint research into insulation and over-cladding. Since the purpose of 

the research was to evaluate a system that might be applied through CEDA Wx programs the 

system had to (1) be composed of components that could be installed by contractors working in 

the Wx programs; (2) be as low cost as practical; (3) not provoke objections from building 

officials and local code officials relative to fire risk; and (4) accommodate at least a nominal R20 of exterior insulation. 

Exterior insulation and finish systems (EIFS) might seem a logical fit for retrofit insulation of 

masonry buildings. Indeed, these systems were initially developed for this application. However, 

the installation of an EIFS would generally require specially trained or franchised contractors. 

Also, the expanded polystyrene substrate used in EIFS systems available in the United States 

would surely raise concerns relative to fire risk. Insulated metal panels have been used in high 

performance retrofits of masonry buildings, but these systems are presumed to represent a cost 

that could not reasonably be considered to be within the reach of Wx programs. Metal panels or 

another cladding system installed over mineral fiber insulation might be an option that would 

satisfy fire safety concerns; however, stand-off brackets or other attachments capable of 

accommodating the desired amount of insulation are not readily available. 

Based on the parameters identified for the retrofit assembly, the research partnership determined 

that the retrofit assembly would include wood furring fastened to the face of masonry, rigid or 

semirigid board insulation, strapping, and fiber-cement siding attached to the strapping. The 

assembly would also include a fully adhered air and water control membrane over the face of the 

masonry. The basic assembly that forms the basis for the retrofit assemblies evaluated in this 

research project is consistent with the recommended cladding design for masonry walls 

identified in previous Building America research (see Baker 2012). An illustration from the 

technical report for this research is reproduced in Figure 5 below. In this assembly, the wood 

furring or framing is attached to the masonry with standard exterior-grade masonry fasteners, the 

strapping is attached to this wood framing with long exterior-grade screws, and the fiber cement 

is attached with fasteners typically used for fiber cement installation. 

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2 × 4 wood studs installed 

on the flat attached to 

masonry wall 

Furring strips or hat channels
 

attached back through the 

insulation to 2 × 4 wood studs
 

Figure 5. Exterior insulation strategy adopted as the basis for the assembly to be 

implemented through the research project 

BSC prepared schematic drawings of the retrofit wall assembly for preliminary discussions with 

the City of Chicago Building Department. The research team’s preferred approach included foilfaced polyisocyanurate insulation, wood framing against the masonry, and wood strapping for 

attachment of fiber cement cladding (Figure 6 and Figure 7). This assembly demonstrates robust 

thermal performance and was also deemed by the research team to provide robust fire resistance 

due to the material nature of fiber cement siding and the fire resistance rating of the specific 

insulation material. 

17
 
 


 

Figure 6. Schematic retrofit assembly, plan view 

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Figure 7. Schematic retrofit assembly, section view 

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BSC also prepared alternatives to this preferred approach in case the city building department 

found the team’s preferred approach unacceptable from a fire risk perspective. Among these 

alternatives were assemblies that substituted semirigid mineral fiber insulation for 

polyisocyanurate and others that used metal hat channels in place of wood strapping for cladding 

attachment. Ultimately the project was able to proceed with an assembly involving wood 

strapping and extruded polystyrene (XPS) insulation behind fiber cement cladding. 

The two candidate buildings that CEDA selected for participation in the research both have 

windows recently replaced and upgraded. Both buildings also have low-sloped roofs with brick 

parapet walls. BSC prepared schematic details for these buildings to address, in a generic 

fashion, window returns, the parapet, and the base of the insulation and over-clad assembly (see 

Appendix A). 

The schematic details show a retrofit assembly consisting of (from face of masonry out): 

•	 Membrane or elastomeric paint over existing masonry 

•	 One layer of 11⁄2-in. rigid insulating sheathing inset between 2 × 4 studs installed on the 

flat 

•	 One layer of 2-in. rigid insulating sheathing with joints offset from underlying layer 

•	 Wood furring strip attached through insulating sheathing to 2 × 4 stud installed against 

the existing masonry 

•	 New cladding. 

In this design, the “membrane or elastomeric paint” layer functions as both a water control and 

an air control membrane. Brick masonry is subject to capillary uptake of water. It is also known 

to pass water through small cracks such as sometimes form between mortar and brick units. The 

research team also does not believe that brick masonry provides robust and lasting airflow 

control. Since the brick is to be covered with insulating sheathing and cladding, preserving the 

appearance of the brick is not a concern. Thus, more readily available and less costly membranes 

could be used. Sealant is indicated as a substrate for the water and air control membrane at inside 

corners around window openings. The 2 × 4 studs provide a framing structure for support of the 

assembly. The wood furring strips provide support for the cladding attachment and provide a 

drainage and ventilation cavity behind the cladding. 

The recently replaced and upgraded windows created a situation where the water management 

details needed to contend with (1) a window remaining in place, and (2) a window opening with 

unknown flashing condition. The details prepared show the water and air control membrane 

returning over the face of the window frame at the head, jambs and sill. The strategy employed is 

one of a face-sealed window opening rather than a drained opening as would have been 

preferred. In the face-sealed approach, water is controlled at the outer face of the assembly and 

sealants are relied upon to prevent water entry at joints. The approach does not have a provision 

to manage water that passes through the window unit or window frame. As noted in a 

communication from BSC to the CEDA project manager: 

These details begin with the assumption that the existing window is performing and 

not leaking through the window frame itself. The details are designed to address the 

20
 
window to wall interface and maintain continuity of the thermal insulation and 

drainage plane (WRB); however, they do not address water leakage through the frame

itself. If there is leakage through the window frames, then the windows should be

repaired or replaced.

The masonry wall does provide some safe storage capacity for minor water infiltration.

However, a water leak could overwhelm this storage capacity. In the absence of flashing beneath 

the window or with improper flashing beneath the window, leakage through the window unit or 

window frame could be directed to where it would damage interior finishes. CEDA was apprised 

of the risk and determined that the long-term risk at the window openings is acceptable. 

The details also show sealant between the trim and the bottom and sides of the existing window 

frame (Figure 8). The new window trim butting to the existing window frame provides a measure 

of protection for the sealant joint that is relied upon for water control (until such time as the 

window is replaced or reinstalled in a drained opening). 

Figure 8. Window sill detail from schematic window details. Note that the water and air control 

membrane (dashed line at exterior face of brick) returns onto the window frame.

Regardless of whether or not leakage through the window frames will require near-term repairs, 

the expected service life of the window is not nearly as long as that of the wall assembly. The 

schematic window details anticipate replacement of the window at some point in the future. The 

window casing trim, window sill trim, trim returns and insulation at window returns are designed 

to be removed (and subsequently reinstalled) without disrupting the insulation and over-cladding 

assembly beyond the window opening. Removing these elements around the window opening 

provides access to the water and airflow control membrane of the insulation and over-cladding 

assembly. This makes it possible for a future window installation to establish a drained opening 

by installing pan flashing below the window and jamb flashing at the sides that properly 

integrate with the water and airflow control of the insulation and over-cladding assembly 

(Figure 9 and Figure 10). 

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Figure 9. Window head detail from schematic window details. Note that removing the window trim, 

trim return, and window return insulation exposes the water and air control membrane (dashed 

line at exterior face of brick) of the assembly. 

Figure 10. Window jamb detail from schematic window details. Note that removing the window 

trim, trim return, and window return insulation exposes the water and air control membrane 

(dashed line at exterior face of brick) of the assembly. 

22
The schematic details show a coil-stock trim return at the head and sides of the window opening 

in order to accommodate insulation at the window returns and to maximize the thickness of 

insulation at the returns. As noted by Baker (2012), insulating the returns of the masonry opening 

is very important for controlling flanking losses. Leaving the masonry surfaces of the opening 

returns uninsulated would amount to leaving significant thermal bypasses. The schematic details 

were developed for a generic window. Depending upon the configuration of the window, 

thickness of the window frame, and location of weeps through the window frame, the existing 

window might accommodate more or less insulation. In communication with the CEDA project 

manager, BSC established that the insulation level at the window opening returns would be no 

less than R-5. 

For the parapet wall, the details prepared demonstrated a connection between the airflow control 

of the wall and that of the roof by a transition membrane that wraps over the top of the existing 

parapet structure and seals to both the membrane or elastomeric paint on the wall and, on the 

roof side of the parapet, the existing roof membrane. The approach represented in the detail also 

illustrated the need to remove the existing parapet cap as the existing cap would be inadequate 

after the wall is thickened with insulating sheathing (Figure 11). Wrapping the parapet with 

insulation also addresses a major heat loss liability represented by this masonry fin projecting 

above the surface of the roof (see Lstiburek 2008) 

Figure 11. Schematic parapet detail. Note the transition membrane that connects the air control 

membrane of the wall (dashed line at exterior face of brick) to the existing roof membrane. 

23
 

 

 

 


 

The parapet cap detail also evinces the opportunity to improve water management at the parapet 

wall with a new metal cap flashing and continuous adhered water control membrane over the top 

of the existing parapet. The roof side of the parapet is detailed to facilitate future replacement of 

the roof and connection of the new roof to the transition membrane. 

CEDA used these drawings in soliciting bids from a selected group of contractors. Because the 

drawings were schematic and somewhat generic in nature—they were developed based on 

photos of the candidate buildings—the contractors needed to interpret how the design intent 

would be adapted to the particular conditions of the building. 

BSC had envisioned developing a wider set of drawings and details specific to each of the 

buildings involved in the research. This would have helped bidding contractors better understand 

the work scope and functional intent. It also would have provided more specific initial direction 

to contractors selected to implement the work. Unfortunately, BSC was compelled to suspend 

work on the project due to uncertainty regarding funding and the continuation of the project. The 

schematic details that were used in soliciting bids became the drawings that contractors used to 

guide initial implementation of the retrofit assembly. 

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7 Assessment 

7.1 Implementation Observations 

This section will focus primarily on the question of feasibility as it relates to measures needed to 

achieve performance. Challenges encountered by the contractors during implementation are 

reviewed, as these are central to the question of feasibility. 

7.1.1 Painted on Air/Water Control 

Both contractors selected to perform the insulation and over-cladding work elected to use an 

elastomeric paint for the water and air control membrane at the face of the existing masonry 

(Figure 12 and Figure 13). 

Figure 12. Commercially available elastomeric paint used by over-clad contractor 

(Credit: Scott Sanders, CEDA). 

Figure 13. (L) Elastomeric paint application at larger multifamily building. Note that sills of 

windows are not painted; (R) Elastomeric paint application at two family building. 

(Credit: Scott Sanders, CEDA) 

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The contractor for the larger multifamily building applied the elastomeric coating in an initial 

application that did not bring the elastomeric coasting onto the window frame, into window 

openings or onto window sills. The contractor correctly noted that these areas would require 

sealant to fill gaps, cracks, and joints, and further explained that sealant would be applied at a 

later point when the building is staged for the next item of work. A problem resulted from this 

plan: when the building was staged, the crew installed framing against the brick before installing 

the sealant and finishing the elastomeric coating application. As a result, framing that was 

installed over the face of the masonry obstructed access for painting and precluded establishment 

of a continuous water and airflow control membrane behind the insulation layer (Figure 14 left). 

Figure 14. (L) Elastomeric paint application not complete around windows and portions of 

masonry surface obscured by wood framing; (R) elastomeric paint application at the two-family 

building covering the window sill and lapping onto the window frame 

(Credit: Scott Sanders, CEDA) 

Another sequence of operation issue emerged from obstructions not removed prior to the initial 

painting. Electrical conduit, gutters and rain leaders, cables, etc. that are present on the face of 

the building at the time of painting create potential areas of discontinuity in the control layer 

(Figure 15). Once these parts of the wall are obscured by framing or other components of the 

assembly, the opportunity for a continuous control layer is lost. 

Contractors at both buildings found that elastomeric paint did not provide a continuous 

membrane over the uneven surface of the masonry. Small holes and depressions in the field of 

the masonry resulted in small voids in the paint coating. The elastomeric paint is applied with a 

roller. The contractors explained that spray application would not be advisable with the close 

proximity of other buildings and of vehicles. Both contractors agreed that back-brushing of the 

roller-applied paint would help fill the smaller gaps and imperfections, but both also pointed out 

that this would make the paint application much more labor intensive. 

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Figure 15. (L) Water and air control layer discontinuous at location of removed electrical conduit 

(blue circle) and gutter brackets; (R) satellite reception dish and associated cables create areas 

that will require touch-up to establish a continuous control layer with the elastomeric paint 

(Credit: Scott Sanders, CEDA) 

A more acute difficulty in establishing a continuous control layer was evident at joints and 

corners around window openings. In many instances the crew appeared to have difficulty in both 

sealing a joint and providing a smooth transition substrate for the water and air control 

membrane (elastomeric paint) (Figure 16 and Figure 17). In still other instances, sealant that had 

been installed previously may have provided a very irregular surface and/or failed to seal the 

joint. One could also observe many joints or cracks where sealant had not been applied. It is 

likely that these were more apparent after the elastomeric paint was applied. Returning to apply 

sealant after the elastomeric paint would be out of the general sequence. 

Figure 16. (L) Window in masonry opening with previously applied sealant; (R) new sealant and 

elastomeric paint applied at window opening. Note persistent gaps at transitions. 

(Credit: Scott Sanders, CEDA) 

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Figure 17. (L) Gap between masonry and lintel; (R) gaps at joints where sealant had not been 

applied as a substrate for the elastomeric paint 

(Credit: Scott Sanders, CEDA) 

7.1.2 Framing 

7.1.2.1 Orientation of Framing 

The contractors at both buildings exhibited conceptual difficulties in implementing framing in an 

exclusively vertical orientation. The contractors initially installed horizontal framing against the 

masonry at 8-ft intervals (Figure 18). The contractor for the larger building surrounded window 

openings with a picture frame of wood framing. The contractor for the smaller building installed 

a piece of horizontal framing at the top of window and door openings. 

Figure 18. (L) Framing installed in a vertical orientation at 16 in. o.c. as well as horizontally at 8-ft 

increments in the field of the wall. Each window opening is also picture framed with the framing 

material; (R) Framing installed against masonry at two-family building with horizontal framing at 

top of window openings and at 8-ft vertical increments. 

(Credit: Scott Sanders, CEDA) 

After seeing photos from the field showing this framing condition, BSC advised the contractors, 

through the intermediary of the CEDA project manager, to stop installing horizontal framing in 

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the field of the wall and around windows. Both contractors installed framing in vertical 

orientation only for the field of the wall on the second of two treated walls at each building 

(Figure 19). One contractor continued to install framing in a horizontal position above windows 

and doors. The contractor for the larger building continued to install framing surrounding around 

each window. 

Figure 19. (L) Framing installed at in a vertical orientation only in the field of the wall. Each 

window opening is picture framed with the framing material. (R) Framing installed against

masonry at two-family building with horizontal framing at top of window openings but in a vertical 

orientation elsewhere. 

(Credit: Scott Sanders, CEDA) 

There are few concerns regarding the horizontal framing within the assembly. First, a horizontal 

member positioned across the water control layer has the potential to impede water from draining 

out of the system. Moisture that dwells in the system presents the risk of damage to moisturesensitive materials—the horizontal pieces of wood framing in this case. Second, this represents 

unnecessary use of material and labor. Third, the unnecessary framing represents a small 

compromise to the thermal performance of the assembly. At a subsequent site visit, BSC 

demonstrated to the contractors how the horizontal framing was not at all needed for cladding 

and trim attachment. 

7.1.2.2 Spacing of Framing 

The schematic drawings of the retrofit wall assembly that BSC prepared for preliminary 

discussions with the City of Chicago Building Department indicated a 24-in. o.c. spacing for the 

furring installed to the face of the masonry (Figure 6 and Figure 7). However, spacing of the 

framing is not indicated on the schematic details that were included in the bidding package. 

The contractor for the larger building spaced the framing installed against the masonry at 16 in. 

o.c. The contractor for the smaller builder also started with 16-in. o.c. spacing for this framing. 

Then this contractor determined that the cladding system could be supported on 24-in. spacing 

(Figure 20). After the installing the first level of framing against the first wall, the crew switched 

to 24-in. o.c. spacing to realize labor and material savings. 

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Figure 20. Strapping over insulating sheathing showing switch from 

16 in. o.c. to 24 in. o.c. at the two-family building 

(Credit: John Yi, CEDA) 

7.1.3 Insulating Sheathing 

Both contractors elected to use XPS rigid insulation board as the insulating sheathing 

(Figure 21). The contractors did not appear to have difficulty cutting and fitting the XPS to fit 

between the furring strips installed to the face of the masonry. 

Figure 21. (L) Crews installing rigid insulation between furring; (R) second layer of rigid insulation 

installed over same section of wall as shown at left. Photo taken 11⁄2 hours after photo at left.

Finished first floor insulation extends another three window bays to the right of the image. 

(Credit: Scott Sanders, CEDA) 

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Both contractors found the installation of insulating sheathing to be more efficient if they 

installed both layers of insulation at a particular section before moving on to the next section. 

This limited the offset of horizontal seams for subsequent layers to a few inches (Figure 22 

below). 

Figure 22. Offset of seams in successive layers of insulating sheathing. Offset for vertical seam is 

limited by the size of insulation boards and the spacing of framing. 

(Credit: Scott Sanders, CEDA) 

Because of the condition of the elastomeric coating over the rough brick surface and the presence 

of horizontal furring installed across the face of this water control layer, BSC advised the 

contractors to tape the seams in the outer layer of insulating sheathing so that it might function as 

a secondary water shedding layer behind the cladding. This proved to be at odds with the 

contractors’ method of using the strapping to hold the insulation to the wall during installation. 

Providing continuous and effective taping of the seams would require intermediate fastening of 

the insulating sheathing so that the face of an area of sheathing could be taped prior to 

installation of the strapping. One or two screws with a washer or roof button per board would be 

enough to provisionally secure the insulating sheathing to the wall and allow the seams to be 

taped without obstruction by the strapping. 

7.1.4 Strapping 

Despite exhibiting a reticence to employ framing in a vertical orientation only, during installation 

of strapping over the insulation, the contractor for the larger building demonstrated comfort with 

limiting strapping to a vertical orientation (Figure 23 and Figure 24). 

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Figure 23. Wood strapping installed in vertical orientation only over face of insulating sheathing 

(Credit: Scott Sanders, CEDA) 

Figure 24. (L) Wood strapping with fastener used for attachment through rigid foam insulation to 

2 × 4 framing; (R) longer size fasteners used to attach strapping through thicker rigid foam

insulation layer at parapet 

At the smaller building the contractor accepted the practice of using only vertically oriented 

strapping in the drainage plane after BSC demonstrated the approach during a site visit 

(Figure 25). 

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Figure 25. (L) BSC personnel explaining the attachment of trim to vertically oriented strapping; 

(R) the same window after the contractor reconfigured the strapping 

(Credit: John Yi, CEDA [L] and Scott Sanders [R], CEDA). 

7.1.5 Parapet 

At both buildings, contractors found the parapet to be in worse condition than they had 

anticipated during the bidding process. 

At the larger building, the parapet wall was significantly out of plumb. The bricks and mortar 

remained relatively intact after removal of the existing parapet cap. The crew foreman devised an 

ingenious method to allow the new cladding system to achieve a flat cladding surface while 

avoiding large gaps in the insulation layer (Figure 26). He found that the 2 × 4 furring could be 

bent and held by the masonry fasteners to the brick wall, and then pieces of beveled roofing 

insulation could be installed between the outer layer of insulating sheathing and the furring to 

true the outer layer of insulation and strapping. Longer screws were needed at this location to 

secure the strapping to the wood furring. The approach maintains a continuous layer of 

compressive resistance between the strapping and wood framing. The compressive resistance of 

the layer between the strapping and the wall is one of the mechanisms that enable the strapping 

to support the cladding weight over a thick layer of insulating sheathing (Baker 2012). 

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Figure 26. Beveled roof insulation used to true new cladding attachment at top of wall. Note that 

fasteners are left loose at the time of this photo. 

(Credit: Scott Sanders, CEDA) 

At the two-family building, the contractor found several courses of brick beneath the parapet cap 

to be loose. The budget for the project did not permit any expansion of the contract to include 

resetting brick or repair to the parapet wall. The contractor proposed a modification to the 

schematic parapet detail to provide a wood frame that contains the parapet and supports cladding 

independent of the parapet. The contractor proposed using a 2 × 12 frame over the top of the 

parapet fastened to the wood furring attached to the face of the wall (Figure 27 Left). At the roof 

side of the parapet the contractor fastened oriented strand board (OSB) to the 2 × 12 (Figure 27 

Right) as a substrate for attaching the insulation and metal counter flashing indicated in the 

schematic parapet detail (Figure 11). 

The contractor’s proposal provided a means to support the insulation, cladding, and new metal 

cap designated for this area. However, it did not provide for continuity of the airflow control 

from the wall to the roof. As seen in Figure 27, the vertical furring at the face of the wall 

prevents the membrane over the top of the parapet from wrapping onto the elastomeric coating 

on the face of the brick. BSC provided an alternate parapet detail for the contractor to implement 

(Figure 28). The contractor slightly modified this detail to install OSB to the inside face of the 

parapet. The perimeter of the roof was then attached to the face of the OSB before a transition 

membrane was wrapped over the parapet and onto the newly reattached roof membrane. 

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Figure 27. (L) Contractors mock up of frame over parapet using 2 × 12 attached to vertical furring 

attached to face of wall; (R) OSB attached to 2 × 12 at inside face of parapet. 

(Credit: John Yi, CEDA) 

Figure 28. Schematic alternate parapet detail providing a frame over the top of the parapet. Note 

the transition membrane that connects the air control membrane of the wall (dashed line at

exterior face of brick) to the existing roof membrane. 

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The finished parapet cover provided an assembly that allows for nondestructive removal of metal 

counter flashing and insulation in order to access the perimeter of the roof membrane for 

replacement (Figure 29). With the layers of insulation to both the inside and outside of the 

parapet, the new parapet was also noticeably wider than it had been previously. 

Figure 29. Finished parapet cover at two-family building 

The contractor at the larger building also encountered difficulty in providing a continuous 

transition of the airflow control over the top of the parapet from the wall to the roof surface. As 

seen in Figure 30, the initial installation of the transition membrane at the top of the parapet 

failed to connect to the elastomeric coating on the face of the wall and was not continuously 

adhered to the roof membrane at the inside face of the parapet. 

Figure 30. (L) Transition membrane not connected to elastomeric coating at face of wall; (R) 

transition membrane not adhered to roof membrane at inside face of parapet 

36
 
In discussing the treatment of the parapet with both contractors at the respective building sites, it 

was apparent that neither had approached the detail with an understanding of the function of the 

transition membrane. In the schematic design of the parapet treatment, the transition membrane 

is to provide a continuous airflow control transition and water control transition connecting the 

elastomeric coating on the face of the wall to the roof membrane. In other words, the transition 

membrane is intended to provide continuity between the air and water control functions of the 

roof and of the wall. Instead, at the initial implementation the contractors installed a piece that 

more or less provided water shedding at the top of the parapet. 

Upon realizing the airflow control function of the transition membrane, both contractors realized 

the need to use wider or multiple pieces of adhered membrane to provide the continuity of 

airflow control. Some of the constructed assembly had to be removed at both building sites in 

order to allow the transition membrane to be installed. The contractors also wrapped the exposed 

ends of the parapet wall with an adhered membrane and insulation. 

7.1.6 Base of Wall

The intent of the schematic detail for the base of the wall was to show contractors how the 

exterior insulation and over-clad assembly could be terminated at the base of the wall and how it 

could be protected from pests that might damage or nest in the assembly.6 The detail shows a 

cladding vent between furring strips at the base of the drainage and ventilation cavity. The detail 

also shows an insect screen that wraps over the base of the assembly from behind the insulating 

sheathing to over the face of the strapping and cladding vent (Figure 31). 

Figure 31. Schematic detail for base of insulation and over-clad assembly

 6 The base of the exterior insulation and over-cladding assembly can be brought closer to grade than the cladding of 

a wood-framed structure. Because the underlying structure is solid masonry, the risk from pests is essentially limited 

to the exterior insulation. The materials of the exterior insulation and over-cladding assembly have robust tolerance 

for moisture exposure as long as the materials are permitted to dry. Therefore, the base of the assembly need only be 

protected against immersion in liquid water.

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At both building sites, the contractor did not install screening material at the base of the wall 

prior to installing insulating sheathing. This required alternate methods for protecting the base of 

the assembly than shown in the schematic detail (Figure 32). 

Figure 32. Base of wall with constricted access for attachment of screening 

(Credit: John Yi, CEDA) 

At the larger building, a conduit pipe at the base of the wall restricted access for attachment of 

the screening. Ironically, the horizontal furring, which was against BSC recommendations, at the 

base of the wall provided an attachment surface for a metal screen material. The cladding 

fastened over the wood strapping was loosened to allow the screen material to be fed underneath 

the cladding to wrap the exposed edge of the insulating sheathing. 

At the smaller, two-family building, the insulation and over-clad assembly extended to very 

close to grade in order to allow the new cladding to align with the sills of the basement windows 

(Figure 33). This provided extremely limited working access for installation of any screening at 

the base of the wall. On the other hand, the concern for pest problems is heightened by having 

exposed edges of foam plastic insulating sheathing this close to the ground and with relative 

protection of the overhang created by the assembly. 

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Figure 33. Base of wall insulation and over-clad assembly very close to grade at the 

two-family building 

During a joint CEDA/BSC site visit, the contractor proposed using perforated soffit material and 

brake forming it to obtain the desired profile for the closure and protection at the base of the 

wall. BSC reviewed the importance of providing a seal between brick and this closure piece to 

prevent bypasses between the brick and the closure piece. The contractor suggested using a 

continuous bead of roofing cement to seal the closure piece to the brick. BSC provided a revised 

detail for the base of the wall incorporating the contractor’s suggestion as discussed and 

reviewed at the building site (Figure 34). 

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Figure 34. Excerpt of revised detail for protection at base of wall insulation 

and over-clad assembly 

The closure piece implemented is sealed to the foundation wall and turns up over the outside face 

of the wood strapping. The perforated soffit material provides protection for the base of the 

assembly as well as screening for the ventilation cavity behind the siding (Figure 35). 

Figure 35. Perforated soffit material use for protection at base of insulation 

and over-clad assembly 

(Credit: Scott Sanders, CEDA). 

7.1.7 Window Surround 

The windows at both over-clad sites had been replaced relatively recently and were to remain in 

place. The windows at the larger building had been replaced through a CEDA Wx program that 

40
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

installed new triple-glazed, low-e, vinyl-framed windows. At the smaller building, the windows 

had been replaced by a program other than the CEDA Wx program two to five years prior to the 

over-clad project. The newer windows at the smaller building appear to be double-glazed, low-e, 

vinyl-framed windows. For both buildings, it is not known how the window openings are flashed 

or whether the windows are installed in a sill pan flashing. The windows appear to be face-sealed 

at the perimeters of the window frames. 

The windows at the larger building are installed directly against the masonry opening and have a 

sealant joint between the masonry and the vinyl frame. At the smaller building, the windows are 

installed in a metal-clad trim/frame surround to the inside of the masonry opening (Figure 36). 

Figure 36. (L) Window set directly in masonry opening at the larger building; (R) windows set in 

metal-clad trim/frame surround at the two-family building 

(Credit: Scott Sanders, CEDA) 

The difference in the window positions relative to the masonry openings led to a significant 

general difference in the installation of the insulation and over-clad around the windows. It 

appears that both contractors interpreted the window detail as indicating that the insulation and 

trim are to be returned to the first nonmasonry element in the window opening. At the larger 

building, the first nonmasonry element in the masonry opening is the vinyl frame of the window. 

When butted to the window frame, the insulation and return trim cover the sealant joint around 

the window (Figure 37). Covering the joint around the window frame is, in fact, the intent of the 

design. At the smaller building, the first nonmasonry element in the masonry opening is the 

metal-clad trim/frame surround. When the insulation and trim return are butted into this element, 

the joint around the perimeter of the window is left exposed (Figure 38).7 

7 It should be acknowledged that the implementing contractor for this building reapplied sealant at the exposed joint 

around the window frame. 

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Figure 37. Return trim at the larger building butting into the vinyl window frame 

Figure 38. Return trim at the smaller building butting into the metal-clad trim surround (blue 

arrows) leaving the joint around the vinyl window frame exposed (red arrow) 

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The implementation of the insulation and over-clad strategy at the window sill revealed 

additional challenges and the need for adjustments to the details. At the larger building, the 

contractor implemented a mockup of the window surround in preparation for a joint site visit by 

CEDA and BSC personnel. The mockup was implemented with a flashing membrane positioned 

over the insulation return at the sill (Figure 39). With the noted discontinuities in the elastomeric 

paint water control membrane, it is important that the adhered sill flashing at the window sill 

perform the function of preventing water from being absorbed into the masonry. 

Figure 39. (L) Contractor mockup of window surround; (R) BSC personnel explaining 

placement of flashing membrane 

(Credit: John Yi, CEDA) 

The schematic details (Figure 40) show the flashing membrane at the sill extending out over the 

face of the cladding but covered by a sill trim piece. The contractor was concerned that the sill 

trim planned would not cover the edge of the membrane and opted, instead, to turn the sill 

flashing membrane onto the outer face of the insulating sheathing (Figure 41). This is acceptable 

given that the strapping cavity over the face of the insulating sheathing is designed and 

implemented to be a drained cavity and given that the cladding and trim system is expected to 

manage the bulk of incident rainwater. 

43
 
Figure 40. Window sill detail from schematic window details. Note that removing the window sill 

trim and window sill insulation exposes the water and air control membrane (dashed line at 

exterior face of brick) of the assembly.

Figure 41. Second mockup of window surround showing the flashing membrane 

placed beneath the insulation return 

(Credit: Scott Sanders, CEDA)

During implementation of the window surround mockup, the contractor noted that 1 in. of rigid 

insulation returning at the sill would bring the sill trim very close to the weep holes of the 

window frame. The contractor purchased thinner rigid insulation boards for situations where the 

window opening could not accommodate 1 in. of rigid insulation. 

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The schematic details from which the contractors were working did not include an explanation of 

the implementation at the corner between the sill and the jamb. Indeed, the corners of the 

masonry openings represent the most vulnerability for water penetration. Ideally, control layers 

at the sill would turn up at the jamb and the control layers of the jamb would lap over the control 

layers of the sill to preserve a shingle lapping and to direct water away from the corner (Figure 

42). The contractor for the larger building devised a sequence whereby the insulation return at 

the sill is installed prior to the insulation return at the jamb and then the sill trim is installed 

continuously across the sill insulation return prior to the jamb trim. On observation of the early 

phase of construction, it appeared that this sequence was not consistently implemented. 

Figure 42. (L) Insulation return at the jamb installed before the insulation return at the sill. Note 

also that the sill flashing membrane does not extend over the outer face of the insulating 

sheathing. This was later corrected. (R) Sill trim installed after the jamb return trim. Sill extensions

are actually cut around the jamb trim. Note that the window sill trim has a kick-out to direct water 

away from the face of the building. 

At the smaller building the sills had a generally low slope that varied between windows. Some 

windows appeared to have a flat precast sill surface. This raised a challenge of achieving 

adequate slope for the rain-shedding layer of the window sill trim while providing adequate 

thickness of insulation and not blocking the weep holes of the window frame. The contractor had 

wrapped insulation returns into the jambs and heads of the windows on this building, but left 

insulation off the sills in anticipation of resolving the questions about treatment of the sill during 

a site visit by CEDA and BSC personnel. During this site visit, it was agreed that the contractor 

would use shims installed above the insulation return to provide a slope to the window sill trim 

and employ several different thicknesses of rigid insulation so that for each window. Insulation 

of the sill return could be as thick as could be accommodated without causing the sill trim to 

block the window frame weep openings. BSC prepared a revised window detail to document the 

approach agreed upon (Figure 43). 

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Figure 43. Revised detail for window sill treatment 

This approach for the window sill had the advantage of protecting the sealant joint beneath the 

frame of the window. The slope given to the window sill trim allowed the trim to pass over the 

existing metal-clad trim/frame surround and butt directly to the vinyl window frame. 

The revised details for the window that BSC prepared also showed insulation and trim returns 

butting into the vinyl window frame at the jamb and head of the window (Figure 44). However, 

because the contractor had already prepared the windows (with the installation of insulation 

returns and blocking) for trim returns that butt into the metal-clad frame/trim surround, the 

contractor was not willing to revise the approach for the jamb and head. The contractor did 

reapply sealant to the exposed joint between the vinyl window frame and metal-clad surround. 

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Figure 44. Revised detail for the window surround at the jamb 

The window head represented an area where the contractors exhibited differing understandings 

of the need for water shedding and drainage. 

Crews at the larger building did provide weep holes at the front edge of the window head return 

trim. However, on a joint site visit during construction of the first wall portion at this building, 

CEDA and BSC personnel found this trim to slope back toward the window in many cases. This 

back-slope at the head trim return is a concern because it would direct any water draining from 

the drainage cavity above the window or on the drainage plane (elastomeric coating on the face 

of the masonry) toward the window rather than away from the window opening. 

CEDA and BSC personnel discussed the need for modification of the detail with the contractor 

and demonstrated the repair to ensure that the crew understood the intent of drainage and 

directing water away from the window. The repair of windows already trimmed required forming 

a new head return trim because the upturned leg was not long enough to provide a positive slope 

to the outside and still attach to the strapping at the head of the window. At the time the backsloping head trim was discovered, the casing trim had been installed around most of the windows 

on one side of building. Rather than cut jamb casing trim to lower the head casing, the head 

return trim was lowered for a consistent 11⁄2-in. reveal at the window head (Figure 45). This 

detail was carried over to the second side of the building. 

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Figure 45. (L) Window head return trim sloping toward the window; (R) CEDA personnel 

demonstrating the reconfiguration of the window head return trim 

During the same CEDA/BSC joint site visit, it was discovered that the contractor had not 

installed a drip cap or diversion flashing above the head casing trim (Figure 46). Without this 

diversion flashing, the top of the head casing presents a horizontal shelf to impede water from 

draining down the cladding surface. In some locations, a poorly executed sealant joint between 

cladding and trim provided an opening where water would likely be directed behind the 

cladding. While CEDA and BSC personnel were on site, they worked with the crew to mock up 

a drip cap that demonstrates a positive slope to the outside and a drip edge to divert water away 

from the face of the building. A brake-formed drip cap was subsequently installed at each 

window head. 

Figure 46. (L) Window head casing with no drip cap and sealant gaps; (R) Contractor project 

manager reviewing the drip cap flashing with the crew 

At the smaller building, the contractor provided a trim return at the window head that not only 

sloped to the front but also had an extra bend at the front edge to channel water toward weep 

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holes (Figure 47). The contractor also installed a cap flashing above the head casing with a 

positive slope to the outside and a kick-out at the lower edge. 

Figure 47. Window head return trim with profile channeling water to weep holes at the front edge 

The experience of the insulation and over-clad implementation at both buildings reveals that 

greater attention is needed at the corner between the sill and the jamb of the window openings in 

order to ensure that this vulnerable interface is adequately protected against water intrusion. For 

example neither CEDA nor BSC received evidence that the sill flashing membrane turns up at 

jambs (or otherwise has end dams). It is also apparent that providing a termination for the top 

horizontal edge of a peel-and-stick type flashing is not common practice. 

7.1.8 Cladding and Finish 

The treated elevations of both over-clad projects present a clean and finished appearance. The 

contractor for each project involved the building owner in selection of cladding and trim colors 

(Figure 48 and Figure 49). 

49
 
 

 

 


 

Figure 48. Finished side of the larger building 

Figure 49. Treated wall at the smaller building striking a contrast with the untreated wall 

at the rear of the building 

50
 
 

 

 

 

 

 

 

 

 


 

The scope for the larger building employed fiber cement panels (4-ft × 8-ft sheets) for the 

cladding. The contractor used cellular polyvinyl chloride (PVC) and metal coil stock for the trim. 

For the smaller building, lapped fiber cement siding was the specified cladding system. The 

contractor for this project used metal coil stock and color-matched cellular PVC for the trim. 

Some differences in treatment emerge from the different cladding types used. 

The lapped siding for the smaller building was factory finished and primed on all sides. The 

panels used at the larger building were not factory primed. The contractor primed the back sides 

and edges of the panels prior to installation and then primed and painted the exposed face of the 

panels when these were installed on the building (Figure 50). 

Figure 50. (L) Fiber cement panels back-primed prior to installation; (R) Progression of panel 

installation and face-priming at the second treated side of the larger building 

(Credit: Scott Sanders, CEDA) 

Early in the project, BSC raised a concern that the cladding system did not receive design 

attention from an aesthetic point of view. Specifically, the butt joints between panels are not 

coordinated with the geometry of the building by, for example, aligning with windows or other 

features on the treated elevation (Figure 51). The visible butt joints in the finished over-clad 

system might detract from the overall appearance of the installation (Figure 52 and Figure 53). 

51
 
 

 


 

Figure 51. Caulked butt joints between 4 × 8 panels 

Figure 52. Butt joints between the panels visible in the finished wall 

52
 
 

 

 

 

 


 

Figure 53. Visible butt joints in the finished wall 

While the lapped siding system is able to hide fasteners, the panel system installed employs 

exposed fasteners. The exposed fasteners might also detract from the appearance of the finished 

system, although this is subjective. The fiber cement panel manufacturer’s installation 

instructions included in the contractor submittal indicates “Z” flashing as an acceptable option 

for horizontal joints between panels. The contractor for the larger building where the panels were 

used elected, instead, to caulk both horizontal and vertical butt joints between panels (Figure 54). 

With the drainage cavity directly behind the panels, the “Z” flashing is not needed to relieve 

water behind the panels. 

Figure 54. (L) Fiber cement lapped siding with fasteners at the top edge concealed by lap of 

subsequent piece; (R) fasteners for the panel cladding system exposed 

(Credit: Scott Sanders, CEDA) 

53
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

7.2 Cost Analysis 

The contract cost for implementing the insulation and over-clad assembly amounted to $23.65/ft2 

gross of treated wall at the larger building. The average for the three (of four total) lowest bids 

for this project amounted to $25.31/ft2 gross. For the smaller building, the implementation cost 

amounted to $11.10/ft2 

gross of treated wall with the average of the three lowest bids at 

$14.43/ft2 gross of treated wall. Wrapped into these cost figures is the cost for treating or 

remediating the parapet and installing a new cap. 

After each implementing contractor either completed the work or completed a substantial portion 

of the work, the implementing contractors were asked to provide an estimate for the cost of 

implementing the insulation and over-clad assembly. This estimate was to reflect experiences 

gained during implementation of the work. This was deemed useful information, as neither 

contractor (nor any of the bidding contractors) had implemented a similar assembly. 

Interestingly, both implementing contractors estimated a unit cost that was close to their original 

bid and lower than the average of the three lowest bids. This is taken as validation of the contract 

cost as representing a mature market unit cost for similar work. 

During interviews with the implementing contractors, the contractors indicated that working 

access at the building site and height of the building are significant factors in the cost of working 

on the exterior of a building. Occupational safety regulations permit access by ladder for work on 

structures up to two stories in height. Above this height, staging or a lift mechanism would be 

required, thus significantly increasing the cost of the job and the resulting unit cost for the 

measure. The contractors involved in this research project indicate that a mechanical lift 

operating from the ground is the least costly and most flexible means to perform exterior 

building enclosure work above two stories. Use of such a lift, however, would require a 

relatively large area of clear and level ground adjacent to the building. Such access is not 

unheard of in urban environments, but is also certainly not to be expected as a general condition. 

The site of the larger building accommodated some work from ladders; however, most of the 

work above the first level required the use of suspended staging. At the smaller building, work 

could be performed with ladder access on one side of the building. On the other side, pipe 

staging was needed due to the tight spacing between the subject building and the adjacent 

building. In fact, even the pipe staging was made feasible only by the fact that the owner of the 

subject building also owns the adjacent building and thus was amenable to allowing working 

access from the adjoining property. Without this accommodation, the side setback would have 

been insufficient to allow pipe staging to be erected. 

One of the contractors implementing the over-clad work provided an estimate of the assembly 

cost under four different basic scenarios of building height and access. Table 1 shows the impact 

of building height and access on the unit cost estimates provided by this contractor. 

Table 1. Height and Access Impact on Insulation and Over-Cladding Costs 

Scenario Unit Cost Impact 

Two stories, easy work access Baseline 

Two stories, difficult access + 9% 

Three or more stories, easy work access + 35% 

Three or more stories, difficult access + 39% 

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The unit costs reflected in bids for the larger building represent a premium of approximately 

75% over unit costs reflected in bids for the smaller building. This premium is greater than 

would be suggested by Table 1 for generalized height and access parameters. Perhaps location 

also factored in to the contractors’ bids. The smaller building is located in a modest-income 

residential neighborhood. The larger building is located in a more densely developed mixed-use 

urban area. The larger building is also enclosed by at least one layer of 12-ft high, razor wiretopped chain link fencing. To a contractor evaluating the project, this fencing might indicate 

greater risk to security of materials, crew vehicles, etc., which would in turn, risk increasing 

costs to the contractor. 

As discussed in Section 4, the costs attributable to the exterior insulation strategy are inextricably 

linked to nonenergy benefits. Therefore, it is not reasonable to compare estimates of energy cost 

savings directly to component costs to derive a measure of cost effectiveness. It is, however, 

useful to compare the assembly as implemented to an over-cladding strategy decidedly not aimed 

at achieving energy benefits. Where the comparison includes components of the exterior 

insulation and over-cladding assembly, then the cost increment between these two different 

assemblies might be associated with a narrower scope of associated benefits. 

Conceivably, fiber cement siding could be installed on furring strips attached directly to a 

masonry exterior. The thermal benefit of such a strategy would be almost inconsequential. The 

noninsulated over-cladding would entail certain nonenergy benefits to the building. These 

benefits, while not quantifiable, can be enumerated. Table 2 below compares the potential 

nonenergy benefits expected from a noninsulated over-cladding strategy to those of the overcladding plus insulation strategy implemented in this study. The noninsulated over-cladding 

strategy in this comparison involves fiber cement siding attached to furring strips or metal 

channels attached directly to a masonry wall. This hypothetical strategy is compared to the 

assembly implemented in this research project. 

55
 
 

 

 

 

 

 

 

 

 

 


 

Table 2. Nonenergy Benefit Comparison 

Nonenergy 

Benefit Noninsulated Over-Claddinga Exterior Insulation Plus Over-Claddingb 

Water 

Management 

Weather 

Exposure 

Comfort 

Aesthetics 

Depending on flashing and water 

diversion details, improved by 

addition of 

• Rain-shedding cladding 

• Drainage cavity 

Reduced weather exposure for 

masonry. May significantly extend 

the service life of mortar (reduce 

the need for repointing) 

While the need for repointing is 

reduced, access for repointing is 

significantly encumbered. 

Limited to no benefit 

Subjective 

Superior water management 

achieved by addition of 

• Rain-shedding cladding 

• Drainage cavity 

• Multiple layers of insulating 

sheathing with face of outer 

layer taped 

• Water and air control membrane 

integrated with flashing of wall 

Reduced weather exposure for 

masonry. May significantly extend 

the service life of mortar (reduce the 

need for repointing) 

While the need for repointing is 

reduced, access for repointing is 

significantly encumbered. 

Freeze-thaw risk is virtually 

eliminated. 

Improved radiant comfort 

Subjective a Fiber-cement siding installed over strapping 

b Fiber-cement siding installed over strapping, two layers of rigid insulating sheathing, and water and air control 

membrane 

While not necessarily a benefit, the noninsulated over-cladding strategy presented in this 

comparison maintains the ability of the masonry wall assembly to dry to the exterior through 

both diffusion and air leakage. The exterior insulation plus over-cladding assembly provides very 

limited to virtually no ability of the masonry to dry to the exterior. With the superior control of 

exterior water loading offered by the insulated system and with adequate control of internal 

moisture loads, there would be no benefit to the masonry being able to dry to the exterior. 

Using R.S. Means data for the Chicago area, the installed cost of the above described 

noninsulated over-cladding can be estimated at approximately $5.50/ft2. It is assumed that this 

cost would be impacted by the same factors that yielded the variation in costs collected through 

the research project for implementation of the insulated over-clad assembly. The cost data 

collected imply that work on the exterior wall at the larger building entail a 75% unit cost 

premium relative to the smaller building. Applying this same premium to the estimated cost for 

the noninsulated over-cladding strategy, the insulated over-clad assembly is estimated to 

represent a $9–$15.60/ft2 cost increment over the noninsulated over-cladding strategy. This cost 

increment could be associated with the resulting energy cost savings aggregated with the relative 

nonenergy benefits enumerated in Table 2. It would not be appropriate to associate this cost 

increment with energy cost savings alone. 

56
 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

Through interviews and during site visits by BSC, the implementing contractors and construction 

crews provided suggestions for reducing the cost of the insulation and over-cladding assembly. 

Both implementing contractors indicated that the strategy was particularly labor intensive. The 

parapet and details surrounding windows were identified as areas requiring particularly high 

levels of labor input. While BSC did not field suggestions of specific alternatives for treating the 

windows and the parapet, certainly a building without a parapet (i.e., a building with a steep 

slope roof) would avoid that cost. 

Both contractors suggested that removing the elastomeric paint layer as a cost saving adjustment 

to the strategy. One contractor suggested that eliminating the paint layer would reduce the unit 

cost by more than $2.50/ft2. This cost reflects the need to generally stage and access the building 

separately for this step of the implementation. 

The insulation and over-cladding strategy implemented at the larger building employed fiber 

cement panel siding comprising 4-ft × 8-ft sheets of material. The contractor explained that 

managing large sheets of material on the side of a building entailed certain challenges (especially 

in the “Windy City”) and required a greater number of personnel to be on site during installation 

to handle material both on the ground and on staging. The contractor suggested that lapped 

siding would represent cost and schedule advantages. When asked, the crew at this project 

agreed that the larger panels entailed installation challenges but also suggested that these are 

balanced by the larger area covered by each panel allowing the cladding operation to progress 

more quickly. A lapped siding alternative was among different scenarios for which the contractor 

for the larger building offered cost estimates. These estimates indicate that the lapped siding 

would result in savings of up to $0.55/ft2 or approximately 3% of total unit cost for the scenario 

involving three or more stories and difficult access. 

One of the implementing contractors suggested that the insulation and attachment substrate for 

the siding could be achieved by nail base panels (OSB laminated to rigid foam insulation). This 

contractor estimated that the cost for an assembly composed of 3-in. thick insulated nail base 

panels, house wrap, and fiber cement siding would have a unit cost savings of approximately 

24% relative to the assembly implemented through the research project. This alternative 

assembly for which the estimate was provided does not include the water and air control 

membrane at the face of the brick or the strapping beneath the cladding. Including these 

components would be necessary for the alternative assembly to provide a similar level of water 

management and durability performance. Including these components in a system based on the 

insulating panels would significantly diminish any relative cost advantage. 

Both implementing contractors suggested the use of closed-cell spray foam on the exterior of the 

building as an alternative to the adhered water and air control membrane and rigid board 

insulation. The rationale for the suggestion was time (schedule) and labor savings. Both 

contractors offered an estimate of the cost of this alternative approach. The contractor for the 

larger building estimated that the closed-cell spray foam-based strategy would represent a 

savings of 1%, the contractor for the smaller building provided an estimate representing a 12% 

savings relative to the retrofit assembly as implemented. 

7.3 Performance Assessment 

Blower door testing was used to measure pre- and post-retrofit air leakage at the smaller 

insulation and over-clad building. Blower door testing was not employed at the larger building 

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because whole-building testing was not feasible given the occupancy situation and size of the 

building. Testing of individual units would have been feasible, but, given the significant and 

variable interunit leakage, it is unlikely that testing of individual units would have provided a 

robust signal as to the impact of the exterior enclosure measure. 

At the initial assessment visit wherein the smaller building was scoped for eligible Wx services, 

the CEDA assessor measured an air leakage rate of 4,270 cfm at 50 Pascals (cfm50), which 

corresponds to 8.7 ACH50 (excluding the basement volume) and 6.4 ACH50 (including the 

basement volume). At a final work inspection visit, CEDA personnel measured the air leakage 

rate to be 2,952 cfm50, which corresponds to 6.0 ACH50 (excluding the basement volume) and 

4.4 ACH50 (including the basement volume). This represents a reduction in measured air 

leakage of approximately 30%. 

A 30% reduction in air leakage would seem very impressive, especially considering that the 

insulation and over-clad assembly affected less than 50% of the above-grade enclosure area or 

only about 60% of the above-grade exterior wall area. 

In fact, other Wx work was performed in conjunction with the exterior insulation and over-clad 

work. The other Wx work performed includes installation of compact fluorescent lamps in some 

of the fixtures, a “major bypass” air sealing package, and installation of door sweeps and weather 

stripping. The “major bypass” air sealing package refers to a standardized package of air sealing 

work used in the CEDA Wx program. CEDA Wx program work orders describe this package 

with standardized language that specifically indicates areas for air sealing as follows: 

•	 Joist spaces under kneewall in finished attic areas. Create a rigid seal under the 

kneewall using rigid material (drywall, 1-in. rigid foam, hard board, etc.). Cut and 

place between the ceiling joists. The perimeter of the barrier should be sealed with 

expanding spray foam (two-part foam). 

•	 Kitchen or bathroom interior soffits. Seal the top of the soffit with a rigid 

barrier that can support the weight of required insulation, fasten and seal to ceiling 

joists and soffit framing with spray foam or caulk. 

•	 Two-level attics in split-level houses. Seal the wall cavity with a rigid barrier 

and seal surroundings with spray foam or caulk.
 

•	 Top of balloon-framed interior and exterior walls. Seal with a rigid barrier and 

air seal with caulk or spray foam.
 

•	 Fur cavity on masonry buildings. Seal the cavity with two-part foam around the
 

perimeter of the attic or roof.
 

•	 Joist penetrations on masonry bandjoist. Seal the perimeters of penetrations
 

with spray foam.
 

•	 Chimneys and fireplaces. Seal the chimney and fireplace and the area around 

them with sheet metal (minimum 28 gauge thickness) and seal with high 

temperature sealant.
 

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•	 Soil stacks, plumbing pipes, and open plumbing chases. Seal joints with spray
 

foam or caulk. If a joint is too large, stuff with fiberglass insulation or cover with
 

a rigid barrier and foam over the top.
 

•	 Housings of exhaust fans and recessed lights. Caulk joints where housing 

comes in contact with the ceiling.
 

•	 Duct boots and registers. Caulk or spray a foam joint between the duct boot or
 

registers and ceiling, wall, or floor finish if ducts are located in the attic,
 

crawlspace, or attached or tuck-under garage.
 

•	 Wiring and conduit penetrations. Seal the joint with caulk or spray foam. 

•	 Duct chases. Smaller openings may be spray foamed or caulked. For larger chase
 

openings, cover with a rigid barrier and seal to ducts and ceiling materials with
 

caulk or spray foam.
 

•	 Bathtubs and shower stalls. Seal from the foundation with spray foam. For
 

larger areas, fasten and cover with a rigid material and seal with spray foam
 

•	 Other openings in the air barrier. Seal with a rigid material, seal with caulk or 

spray foam depending on the size of opening.
 

Because this is a standardized or “boilerplate” scope, not all of the items indicated would be 

applicable to a given building. For example, work items relative to “joist spaces under 

kneewall,” “two-level attics,” “duct boots and registers,” and “duct chases” would not apply to 

the two-family building included in this research project. 

The remaining items listed in the Wx air sealing work scope would be generally expected to have 

a significant aggregate impact on air leakage. It is worth noting that most of the remaining items 

on this list that might apply to the two-family over-clad building also happen to address air 

leakage between conditioned space and an attic and that the attic may not be well connected to 

the exterior. This particular building has a shallow attic beneath a low-sloped membrane roof. 

Air leakage through the membrane roof is expected to be of very small magnitude. The 

deliberate provisions for venting of the shallow attic space were also observed to be quite 

limited. Given the configuration of the attic and of the roof it is conceivable that the initial air 

leakage through the attic would have been a relatively minor component of the total measured air 

leakage. 

Unfortunately, it is not possible to differentiate between the air leakage reduction resulting from 

the Wx work on the one hand and the insulation and over-cladding scope on the other, because 

both of these were implemented in the time between the prework blower door measurement and 

the postwork blower door measurement. A case can be made, however, that the exterior 

insulation and over-cladding treatment rendered leakage across the attic floor less significant in 

overall leakage, as connections between the attic and exterior are reduced. The incidental leakage 

through the exterior walls surrounding the attic and through the parapet would be expected to be 

blocked by the exterior insulation and over-cladding treatment. By extension, comprehensive 

treatment of the exterior wall system (all four sides) in a building with a low-sloped roof would 

essentially bring the attic within the pressure boundary. It follows, then, that virtually all of the 

59
 
 

 

 

 

 

 

 

 

 

 


 

air leakage reduction potential from treating the attic floor would be subsumed by a 

comprehensive treatment of the exterior wall system. 

7.4 Simulation Analysis 

7.4.1 Description of Simulation Models 

The simulation analysis is performed to provide a perspective on the energy performance impact 

of the exterior insulation and over-cladding measure. The analysis employed the BEopt energy 

simulation tool. The analysis software is also used to illustrate the energy performance impact 

relative to the total measure cost. While the implementation of the measures was limited to 

portions of two buildings, the simulation analysis evaluates a scenario of a more comprehensive 

enclosure retrofit. 

Because the focus of the study is an enclosure measure, the primary focus of the simulation 

evaluation is the relative impact of the measure on heating and cooling energy use. The total 

simulated energy usage reflects influences of systems and equipment that are outside the purview 

of the current study. In a sense, the total energy usage, reflecting internal loads and mechanical 

system efficiencies, may cloud the evaluation of the enclosure measure. Nonetheless, some 

approximation of these other loads and systems is needed to be able to project a general case of 

the net impact that the enclosure measures might have on a building in operation. 

Some abstraction was needed to model the performance of a multifamily building using the 

BEopt simulation tool. The tool is set up to model single-family occupancies. Rather than 

attempting to create a model of a suitably representative single dwelling unit within the building, 

the simulation analysis pursued representation of the entire building by scaling various inputs to 

reflect the occupancy within the building. The model of the smaller building employed scaling of 

inputs to represent a two-family occupancy. The larger building includes approximately 84 

single-occupancy rooms with shared facilities at each floor; the occupancy and internal load 

intensity were estimated as equivalent to 28 single-family units. The internal gains from major 

appliances were adjusted to represent the occupancy and expected use intensity within the 

building enclosure. This was intended to provide a rational representation of the additional 

cooling load and offset to heating load resulting from the multifamily occupancy. The modeling 

confirmed our expectation that the effect of internal gains on heating and cooling load is not 

prominent in the Chicago climate and for the level of enclosure thermal performance evaluated. 

The simulation reflects another significant abstraction in that the same thermal modifications are 

modeled for all exterior walls of the building. The exterior insulation and over-cladding strategy 

evaluated in this research is not necessarily intended as a system to be applied on all sides of a 

building. In fact, given the articulated and finely executed street façade typical to brick masonry 

buildings in Chicago, the exterior insulation and over-cladding strategy would typically only be 

considered for the non-street elevations. In other words, while budget constraints limited the 

implementation of the strategy to portions of two buildings, even with unlimited funding, the 

research team would not have proposed implementing the strategy on the front side of these 

buildings. BEopt does not currently support different levels or types of insulation on different 

60
 
 

 

 

 

 

 

 

 

 


 

walls. The BEopt models presented here simulate only the hypothetical scenario in which it is 

possible to treat all walls in a substantially equivalent manner.8 

BSC prepared simulation models to represent each of the buildings involved in the research 

study. Major inputs used to describe the building components are listed in Table 3 and Table 4. 

8 It is not inconceivable that the street façade of the building would be treated to approximately equivalent 

performance. In fact, the exterior insulation and over-cladding assembly was initially conceived as a complement to 

interior insulation of masonry as evaluated by Straube et al. (2012) that could certainly achieve similar levels of 

performance. Because of the complex needs of buildings and building owners, a variety of enclosure strategies are 

often needed to achieve comprehensive enclosure upgrades. 

61
 
 

 

 

 

 

 

 

 


 

Table 3. BEopt Modeling Inputs for Two-Family Building 

Building 

Component Baseline Parameter Parameter Upgrades and Alternatives Evaluated 

Cost of 

Upgrade Cost Source 

Infiltration 8.7 ACH50 6 ACH50 (30% reduction) Included in 

other costs N/A 

Attic/Roof 

Insulation R-10 continuous R-40 continuous $2.82/ft2 BEopt library 

Above-Grade 

Walls 

6-in. hollow concrete 

masonry unit (CMU) 

(selected to represent 

uninsulated 3 wythe brick 

masonry) 

Step 1: 6-in. hollow CMU with R-4.6 

continuous insulation exterior 

(selected to represent 11⁄2-in. XPS 

between wood 2 × 4 on flat at 24 in. 

o.c. and cladding) 

$11.12/ft2 

Derived from 

contractor’s 

postconstruction cost 

estimates 

Step 2: 6-in. hollow CMU with R15.7 continuous insulation exterior Derived from 

(selected to represent Step 1 

assembly with addition of continuous $14.82/ft2 contractor’s postconstruction cost 

2-in. XPS layer and strapping to estimates 

support cladding) 

Step 3: 6-in. hollow CMU with R25.4 continuous insulation exterior 

(selected to represent Step 2 

assembly with addition of 2nd 

continuous 2-in. XPS layer) 

$16.82/ft2 

derived from 

contractor’s 

postconstruction cost 

estimates 

U = 0.34, solar heat gain 

coefficient = 0.30 

Windows (estimated representation No upgrade N/A N/A 

of recent Wx window 

upgrade) 

62
 
 


 

Building 

Component Baseline Parameter Parameter Upgrades and Alternatives Evaluated 

Cost of 

Upgrade Cost Source 

Basement 

Refrigerator 

Stove 

Lighting 

Heating System 

Cooling System 

Ventilation 

Domestic 

Water Heater 

Uninsulated 

2 units, 

960 kWh/yr total 

2 units, 

56 therms/yr total 

Building Americaq 

Benchmark 

80% annual fuel utilization 

efficiency, gas-fired boiler 

10 seasonal energy 

efficiency ratio window 

units 

No mechanical ventilation 

Standard gas-fired, energy 

factor 0.59 

No upgrade 

(in acutal application, the exterior 

wall treatment would extend to 3–4 ft 

of above-grade basement wall) 

No upgrade 

No upgrade 

No upgrade 

No upgrade 

No upgrade 

No upgrade 

No upgrade 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

63
 
 

 

 

 

 


 

Table 4. BEopt Modeling Inputs for Larger Multifamily Building 

Building 

Component Baseline Parameter Parameter Upgrades and Alternatives Evaluated 

Cost of 

Upgrade Cost Source 

Infiltration 7.2 ACH50 5 ACH50 (30% reduction) Included in 

other costs N/A 

Attic/Roof 

Insulation R-10 continuous R-40 continuous $2.82/ft2 BEopt library 

Above-Grade 

Walls 

6-in. hollow CMU 

(selected to represent 

uninsulated 3 wythe brick 

masonry) 

Step 1: 6-in. hollow CMU with 

R-4.6 continuous insulation 

exterior (selected to represent 11⁄2 

in. XPS between wood 2 × 4 on 

flat at 24 in. o.c. and cladding) 

$15.96/ft2 

Derived from 

contractor’s post 

construction cost 

estimates 

Step 2: 6-in. hollow CMU with 

R-15.7 continuous insulation 

exterior (selected to represent 

Step 1 assembly with addition of 

continuous 2-in. XPS layer and 

strapping to support cladding) 

Step 3: 6-in. hollow CMU with 

R-25.4 continuous insulation 

exterior (selected to represent 

Step 2 assembly with addition of 

2nd continuous 2-in. XPS layer) 

$21.28/ft2 

$23.28/ft2 

Derived from 

contractor’s post 

construction cost 

estimates 

Derived from 

contractor’s post 

construction cost 

estimates 

U = 0.20, solar heat gain 

Windows coefficient = 0.20 (recent 

Wx window upgrade to 

triple-pane vinyl windows) 

No upgrade N/A N/A 

Basement Uninsulated No upgrade N/A N/A 

64
 

 

Building 

Component Baseline Parameter Parameter Upgrades and Alternatives Evaluated 

Cost of 

Upgrade Cost Source 

Refrigerator 

Stove 

Lighting 

Heating System 

Cooling System 

Ventilation 

Domestic 

Water Heater 

28 units, 

13,440 kWh/yr total 

28 units, 

822 therms/yr total 

100% fluorescent 

hardwired 

80% annual fuel utilization 

efficiency, gas-fired steam 

boiler 

10 seasonal energy 

efficiency ratio window 

units 

No mechanical ventilation 

Standard gas-fired, energy 

factor 0.59 

No upgrade 

No upgrade 

No upgrade 

No upgrade 

No upgrade 

No upgrade 

No upgrade 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

N/A 

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The above-grade wall upgrade was represented in multiple steps in the model in order to evaluate 

the impact of declining costs and diminishing returns for subsequent layers. As discussed 

previously in this report, the larger part of the expense and the majority of the nonenergy benefits 

are encountered in the application of the first layer of insulation and over-cladding. The first step 

in the wall upgrade represents the following: 

•	 The application of the water and air control membrane at the face of the masonry 

•	 Installation of 2 × 4 wood framing to the face of the masonry 

•	 Installation of 11⁄2-in. thick rigid insulating sheathing against the masonry between the 2 × 

4 wood framing 

•	 Installation of fiber cement siding. 

Strapping was not included in this first step because it is conceivable that the cladding could be 

attached directly to the 2 × 4 wood framing. The second wall upgrade represents the measures in 

the first step additional measures as follows: 

•	 Installation of continuous 2-in. thick rigid insulation 

•	 Installation of wood strapping with long screws attached through insulation to framing. 

The continuous insulation added in this step is of a thickness that would require strapping or 

furring for cladding attachment. While representing an appreciable expense and offering no 

discernible energy savings, the strapping creates a drainage cavity behind the cladding, which is 

important for durability of the cladding and water management. 

The third step includes an additional layer of continuous 2-in. thick rigid insulation. The 

incremental cost represents the installation of this rigid insulation and the cost increment for 

longer screws needed to attach the strapping. This step was not implemented at the research 

project sites. However, the schematic design for the assembly that BSC prepared for CEDA’s 

preliminary discussions with the City of Chicago Building Department included two layers of 

continuous rigid insulation. 

An upgrade to the continuous roof insulation is included as an upgrade step to represent a 

comprehensive upgrade of the above-grade enclosure. 

Baseline air leakage inputs represent a measurement for the two-family building and an estimate 

for the larger multifamily building. Section 7.3 explains how the measured air leakage reduction 

resulting from application of the exterior insulation and over-cladding assembly on a portion of 

the above-grade wall plus some other Wx measures can be taken as an approximation of air 

leakage reduction that would result from comprehensive treatment of the above-grade walls. 

The mechanical systems and internal load component inputs are taken to represent typical 

conditions for these types of buildings. 

7.4.2 Simulation Results 

The simulation predicts that the exterior insulation and over-cladding strategy implemented in 

the research project would reduce heating energy use by about 47% for the two-family building 

and about 44% for the larger multifamily building. The simulation confirms that the relative 

magnitude of cooling energy use is fairly small. Predicted reductions in cooling energy use are 

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about 41% for the two-family building and about 39% for the larger multifamily building 

(Figure 55 and Figure 56). It should be noted that both buildings have cooling provided by 

window air-conditioning units only. Although the model simulates cooling energy use for the 

whole building, few of the dwelling units in the larger building actually have window airconditioning units installed. 

Figure 55. Predicted heating and cooling energy end uses for the two-family building 

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Figure 56. Predicted heating and cooling energy end use for the larger multifamily building 

In the simulation, a 30% reduction in air leakage was associated with the exterior insulation and 

over-cladding measure. It is interesting to note that a significant portion of the predicted 

reductions in heating energy use result from reduced infiltration. By comparing the simulation 

predictions for heating energy use represented in Figure 56 with those represented in Figure 57, 

it is apparent that the air leakage reduction associated with the measure accounts for 

approximately one third of the heating energy use reduction in the case of the larger building. 

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Figure 57. Predicted heating and cooling energy end use for the larger multifamily building 

without accounting for air leakage reduction 

The charts shown in Figure 58 and Figure 59 below represent the relationship between 

annualized energy-related costs to total source energy savings for the building as predicted by the 

simulation. The annualized energy-related cost is a composite of predicted annual energy cost 

plus the cost of the upgrade measures amortized over a 30-year term at a 5% rate. In the charts 

the numbered points correspond to scenarios in the model where: 

Point (1) represents the baseline case. 

Point (2) represents the over-clad assembly with 11⁄2 in. of insulation between 2 × 4 wood 

framing. 

Point (3) represents the over-clad assembly with 11⁄2 in. of insulation between 2 × 4 wood 

framing and 2 in. of continuous insulation. 

Point (4) represents the over-clad assembly with 11⁄2 in. of insulation between 2 × 4 wood 

framing and 4 in. of continuous insulation. 

Point (5) represents the over-clad assembly with 11⁄2 in. of insulation between 2 × 4 wood 

framing and 4 in. of continuous insulation, plus a roof upgraded to R-40 continuous 

insulation. 

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Figure 58. Predicted annualized energy-related costs and source energy savings for the twofamily building under four upgrade scenarios 

Figure 59. Predicted annualized energy-related costs and source energy savings for the larger 

multifamily building under four upgrade scenarios 

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The predicted annualized energy-related costs are lower than the baseline case for all upgrade 

scenarios in the simulation of the two-family building. This would suggest that the value of the 

energy savings benefit from the upgrade measures exceeds the amortized cost of the measure. 

For the larger multifamily building, the simulation predicts that each of the upgrade scenarios 

represents a significant increase in annualized energy-related costs. This suggests that the 

amortized cost of the measure exceeds the value of the energy savings benefit from the upgrade 

measures. The comparison of the value of energy savings relative to amortized cost of the 

upgrade is an expression of the cost effectiveness of the measure with respect to energy savings 

or energy savings cost effectiveness of the measure. 

This energy savings cost effectiveness difference observed between the two-family and larger 

multifamily building results from a significant difference in costs for the upgrade measures. As 

discussed above in Section 7.2, the building height and access conditions have a significant 

impact on the unit cost of the exterior insulation and over-cladding measure. One can deduce that 

with constrained access and building height above two stories, the amortized cost of the 

insulation and over-cladding assembly exceeds the value of the energy savings. 

Energy savings cost effectiveness is not an adequate expression of general or overall cost 

effectiveness, because it does not include recognition of values beyond energy savings that might 

be represented in the measure. For example, the primary or most valued benefit from a building 

owner’s perspective might be one of aesthetic improvement or increased durability with respect 

to moisture risks. 

The exterior insulation and over-cladding assembly studied in this research provides significant 

benefits that are not represented in energy costs. While it may not be possible to quantify the 

value of these nonenergy benefits, it is possible to identify components within the assembly that 

do not provide energy savings benefits but that do provide a significant portion of the nonenergy 

benefits. As discussed in Section 7.2, when the cost for these components are subtracted from the 

overall measure costs, the analysis can compare the value of energy savings to costs that are 

more nearly (but not perfectly) associated with the energy benefits. 

Section 7.2 compared the relative nonenergy benefits of a noninsulated over-cladding assembly 

to those of the exterior insulation and over-cladding assembly (Table 2). This comparison 

presumes it is conceivable that a building owner might over-clad a masonry building without 

adding insulation in order to achieve the nonenergy benefits associated with this approach. While 

the noninsulated over-cladding assembly did not offer exactly the same level of nonenergy 

benefits, the nonenergy benefits are, at least, similar. The difference in energy performance 

benefits between the insulated and noninsulated over-cladding assemblies is more or less 

equivalent to the net energy benefits of the insulated over-cladding assembly. Therefore, 

subtracting the cost of the noninsulated over-cladding from that of the insulated over-cladding 

measures yields a net energy-related measure cost that can be associated with net energy 

benefits. 

Figure 60 and Figure 61 below are similar to Figure 58 and Figure 59 with an important 

difference: the amortized measure cost represents only the cost increment between the estimated 

cost of the noninsulated over-cladding assembly and that of the insulated over-cladding 

alternatives. 

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Figure 60. Predicted annualized energy-related costs and source energy savings for the twofamily building under four upgrade scenarios using net energy-related measure costs 

Figure 61. Predicted annualized energy-related costs and source energy savings for the larger 

multifamily building under four upgrade scenarios using net energy-related measure costs 

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As might be expected, the simulation results for the two-family building show a stronger 

reduction in annualized energy-related costs for the exterior insulation and over-cladding 

measures when the cost of the noninsulated over-cladding is subtracted from the upgrade 

measure costs. For the larger multifamily building, the simulation still predicts an increase in 

annualized energy-related costs with each of the upgrade scenarios. However, the first insulated 

over-cladding scenario has a relatively small impact on annualized energy-related costs. 

This comparison is somewhat contrived because, in reality, one would not install the exterior 

insulation without the nonenergy-related components. On the other hand, it is conceivable that 

the over-cladding would be installed without insulation. 

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8 Conclusions 

The observations and collected data from just two implementations of the exterior insulation and 

over-cladding approach provide valuable lessons and insights. These lessons and insights provide 

answers to questions pertinent to broader adoption of the approach. 

8.1	 Under what conditions or for which common building situation is the 

strategy recommended? 

The approach demonstrated through the research projects provides a unique solution for certain 

situations where opportunities are otherwise nonexistent. Some of the benefits of the approach 

depend upon the circumstances of the building. Conditions of access can render the strategy 

more or less costly and may impact whether the strategy is appropriate for a particular building. 

The strategy is recommended where the following circumstances apply: 

•	 Noninsulated masonry bearing-wall construction 

•	 Exterior wall does not provide satisfactory performance in terms of comfort, energy use 

and/or water management 

•	 Occupied building where retrofit activities must minimize disturbances to the interior 

•	 The masonry exterior is not regarded as providing a significant positive contribution to 

the character or aesthetics of the building. 

The following factors tend to favor application of the exterior insulation and over-cladding 

strategy: 

•	 Building has ample working area around the base. 

•	 Building has fewer than three stories. 

•	 There is appreciable (and appreciated) ongoing expense to maintain the masonry. 

The following factors tend to complicate application of the exterior insulation and over-cladding 

strategy: 

•	 Building has restricted working area around the base. 

•	 Building has three stories or more. 

•	 Fire escape or deck that cannot be independently supported is attached to the building. 

•	 Need for significant repairs to the masonry. 

The application of the exterior insulation and over-cladding strategy is not recommended in the 

following conditions: 

•	 Highly articulated and/or high quality brick that contributes to a façade that is an 

important positive benefit to the character or aesthetics of the building
 

•	 Constrained access that cannot support work on the exterior of the building. 

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For typical Chicago brick masonry buildings, the strategy would not be recommended for the 

street elevation. The exterior insulation and over-cladding is more likely to be suitable for the 

side and rear elevations. 

8.2 What are the significant challenges to implementation? 

Significant challenges to implementation of the exterior insulation and over-cladding strategy 

include: 

• Cost 

• Working access 

• Obstructions on the wall surface 

• Irregularities in existing construction 

• Aesthetic coordination. 

Despite indications that the strategy can be cost effective in either a broad or an energy costspecific sense, the significant expenditure is likely to present a barrier to wider adoption. The 

simulation analysis shows that the strategy can reduce annualized energy-related costs for 

smaller buildings. In the case of the studied larger building, for which the unit installation costs 

were considerably higher, the simulation did not show a reduction in annualized energy-related 

costs. However, sophisticated owners of larger buildings are also more likely to value the 

nonenergy benefits of, for example, reduced maintenance cost, improved resident comfort, and 

elimination of freeze-thaw risk. Given the significant initial outlay represented by the strategy 

along with the durability of the energy and nonenergy benefits, the strategy may prove a good 

candidate for special financing programs such as on-bill financing or low-interest loans that 

reduce the required initial outlay on the part of the building owner. 

As noted several times in this report, the cost of implementation is significantly influenced by the 

working access to the building, as well as the general conditions of the site in terms of criteria 

such as perceived security. While constrained access and concerns for security of the site can 

make the implementation prohibitively expensive, there are also likely to be situations where 

very small distances between adjacent buildings render any work to the exterior of the building 

practically impossible. 

Major obstructions include decks, stairs, and fire escapes supported by the masonry wall. If the 

obstruction cannot accommodate the thickness of the exterior insulation plus cladding and the 

obstruction cannot be moved (for cost or feasibility reasons), the obstruction may preclude the 

exterior insulation and cladding strategy for that section of wall. 

Minor obstructions include elements such as gutters, conduits, and satellite dishes. Performance 

of the system is compromised if these are left in place. These obstructions should be removed 

from the wall to be treated prior to application of the water and air control membrane. 

It is common for masonry walls of older buildings to exhibit spalling or other flaws in the bricks 

and to be out of plumb, not true, and/or not straight. A first order of concern with such 

irregularities is to ensure that the structure is fundamentally sound. Provided these irregularities 

do not present concerns for structural stability, challenges may remain for implementation of an 

exterior insulation and over-cladding assembly. The over-cladding assembly may also be viewed 

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as an opportunity to address irregularities in the wall, such as demonstrated at the larger research 

project where the contractor was able to provide a flat and true cladding surface over a wall that 

was significantly out of plumb toward the top. 

Other common irregularities or idiosyncrasies of a building that would affect implementation of 

an exterior insulation and over-cladding assembly include inconsistent dimensional relationships 

between windows and window openings (as exhibited at both research project sites) and 

inconsistent slopes and profiles of existing sills (as exhibited at the two-family building). These 

factors require some flexibility in the details affected by these inconsistent existing building 

elements. Still, in some cases, it may be difficult to anticipate inconsistencies. Inconsistencies 

discovered during construction may render design details infeasible (e.g., materials do not fit) or 

nonperforming (e.g., materials block weep holes). 

Particularly if using large panel cladding, it can be challenging to provide an installation of 

cladding that coordinates aesthetically in terms of, for example, cladding joints aligning with 

building elements. In order to ensure that the over-cladding assembly contributes to the 

appearance of the building, it is useful to have the layout of the cladding deliberately designed. It 

is likely that aesthetic coordination will result in designs that do not use the materials exclusively 

in the factory-supplied dimensions. This will likely increase both material and labor costs. On the 

other hand, if the over-cladding is seen as detracting from the appearance of the building, it is 

less likely to gain wider adoption. 

8.3	 What level of airflow control improvement can be expected with the 

strategy? 

For the building where the air leakage for the entire building was measured both before and after 

the retrofit, it was found that a 30% reduction in air leakage measurement could be achieved 

through the exterior insulation and over-cladding strategy in combination with some Wx 

measures. For the particular low-sloped roof building that was the subject of this research, it is 

likely that the majority of the air leakage reduction from attic air sealing measures would be 

subsumed by comprehensive treatment of the exterior wall system (i.e., all four sides). Therefore, 

it is predicted that an air leakage reduction of greater than 30% would be achieved through 

comprehensive treatment of the above-grade walls of this building. 

Clearly, the configuration of the building was a significant factor in the overall air leakage 

reduction achieved in the study project. While measurement of a single building does not permit 

prediction of specific performance improvements for other buildings, it is reasonable to suggest 

that, for buildings with a low-sloped membrane roof in good condition, the exterior insulation 

and over-cladding approach would be likely to result in very significant reductions in the 

buildings overall air leakage. 

For buildings with a steep-sloped roof or nonmembrane roof, the air leakage performance is 

expected to be highly dependent on the airflow control of the attic floor or roof (see Neuhauser 

2012). The exterior insulation and over-cladding would be expected to bring significant 

reductions in overall air leakage only where the attic floor plane or roof already offers relatively 

robust airflow control. In such cases, the exterior wall measure is well positioned to address a 

significant portion of the remaining air leakage for the building. 

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8.4 What risks inherent in implementation of the strategy must be addressed? 

Inherent risks introduced by the system are limited. It is possible that the reduction in outward 

drying would be perceived as a risk and that this perception would create barriers to 

implementation. The use of foam plastic insulation in the assembly presents risks that are 

managed by proper implementation. Both the perceived risk of limited outward drying and the 

real and manageable risks associated with foam plastic insulation are discussed below. 

8.4.1 Limited Outward Drying 

The exterior insulation and over-cladding approach reduces risks to the building. Because the 

assembly protects the masonry structure from incident rainwater through multiple layers of 

control, the most significant risks to the durability of the structure are removed. Providing a 

significant amount of thermal resistance to the exterior of the masonry assembly maintains the 

masonry within a very stable thermal environment. This removes structural stresses that 

otherwise result from thermal cycling. Throughout much of the year in a heating climate, 

masonry behind the exterior insulation and over-cladding will also be significantly warmer than 

noninsulated or interior-insulated masonry. Because the brick masonry is warmer, it will have 

higher inward drying capacity and also have greater capacity to safely store moisture. In essence, 

the wall is much less likely to get wet and even if it does get wet, it is much less vulnerable to 

damage resulting from wetting due to an increased ability to dry inward and an increased 

capacity to safely store moisture. 

The exterior insulation and over-cladding assembly limits drying to the exterior. The water and 

air control membrane and rigid board insulation applied over the face of the brick masonry will 

essentially prevent evaporation and convective transfer of moisture from the masonry to the 

exterior. The layers of rigid board insulation within the exterior insulation and over-clad 

assembly significantly impede vapor diffusion through the assembly. However, this limited 

drying does not represent an inherent risk relative to leaks through or in the existing enclosure, 

nor does it represent an inherent risk relative to moisture within the exterior retrofit assembly as 

a result of the simultaneous increase in inward drying and increased capacity for moisture 

storage. 

Because the exterior insulation and over-cladding assembly protects the existing masonry from 

incident rainwater, the likelihood of leakage from the exterior through the masonry is greatly 

reduced. Proper design and implementation of the exterior insulation and over-cladding assembly 

control rainwater such that it is drained and directed away from the existing wall. In both of the 

exterior insulation and over-cladding projects included in this study, the existing windows 

remained in place. There was no evidence that these windows had been installed in a drained 

opening. Without a pan flashing beneath the window, water that passes through the window unit 

or through or around the window frame will leak into the wall or into the interior. The thickness 

of the exterior insulation and over-cladding shield the opening and thereby significantly reduce 

incident rainwater reaching the opening. The generally warmer masonry has increased capacity 

to both store water and dry to the interior. Therefore, even with limited to no drying to the 

exterior, the exterior insulation and over-cladding strategy decreases the risk that leakage 

through openings leads to accumulation of moisture. 

The exterior insulation and over-cladding assembly implemented through this research project is 

designed to control water at the face of the existing masonry (with the adhered water and air 

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control membrane), at the exterior face of the insulating sheathing (behind the drainage cavity), 

and at the face of the cladding. Despite the fact that the assembly may include impermeable 

insulation materials and that these materials are installed in continuous layers, there remains 

space for drainage and limited drying in the gaps between individual pieces and in the threedimensional airflow networks that these gaps create. The wood framing installed against the 

masonry and the wood strapping over the face of the exterior insulating sheathing represent 

moisture-sensitive materials within the assembly. By design, these moisture sensitive materials 

are installed in a vertical orientation only in order to facilitate drainage of liquid water by 

gravity. 

We have found in the course of this study and in other experience that contractors are, at least 

initially, resistant to the concept of installing furring and strapping in a vertical orientation only. 

This is a risk associated with implementation but not inherent in the system itself. When framing 

against the masonry or strapping in the drainage cavity is installed in a horizontal position, 

drainage is impeded and there is increased risk that water will dwell longer within the system and 

upon moisture-sensitive materials. Strapping in the drainage cavity would be able to dry by 

diffusion into the drainage cavity. Drying of moisture collecting on strapping in the drainage 

cavity may be aided by ventilation of this cavity. Both in the case of the horizontal strapping in 

the drainage cavity and horizontal framing against the masonry, it cannot be assured that the 

drying potential available would be able to balance the accumulation of moisture caused by the 

horizontal orientation. However, there is sufficient redundancy within the over-cladding 

assembly that localized decay at isolated horizontal wood members will not jeopardize the 

system. 

The changed moisture dynamics associated with limited outward drying through the exterior 

insulation and over-cladding assembly are addressed by the following measures: 

•	 Flash openings to drain to the exterior, OR, if openings cannot be flashed, protect the 

primary sealant joints and provide a means to replace or repair the element in the opening 

without disrupting the surrounding assembly. 

•	 Provide flashing above openings with a drip edge or kick-out at the outer face of the 

assembly. 

•	 Investigate the building for any existing water leakage issues. Remediate the issues 

before implementation of exterior insulation and over-cladding. 

•	 Promote drainage from and within the assembly. Avoid elements that might impede 

drainage such as horizontal framing or strapping. 

•	 Provide ventilation within the building to manage residual exterior generated or interior 

generated moisture. 

8.4.2 Foam Plastic Insulation 

Solid brick masonry assemblies offer superior resistance to combustion. Solid masonry 

assemblies tend not to provide habitat for vertebrate pests. The exterior insulation and overcladding assembly introduces risks in that: 

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•	 Foam plastic insulation is a combustible material. 

•	 The foam plastic insulation as well as the drainage cavity behind the cladding has the 

potential to provide habitat for pests. 

These risks are managed by the following measures: 

•	 Cover the exterior insulating sheathing with noncombustible cladding. 

•	 Provide screening for openings to the drainage and ventilation cavity between the
 

cladding and the exterior insulating sheathing.
 

•	 Provide protection for edges of insulation not covered by the cladding, such as at the base 

of the wall or at vertical transitions. 

8.5 What are the recommended practices critical to achieving performance? 

Observation of implementations of the exterior insulation and over-cladding approach inform 

both general and specific recommendations relative to the performance objectives of the 

assembly. 

8.5.1 General Recommended Practice 

Upon observation of the construction process, it was evident that the crews for each of the two 

projects were competent and resourceful. Still, errors occurred that resulted either in the need to 

correct implemented work or in compromises to the performance of the assembly. Most of these 

errors can be traced to a lack of understanding of the functional intent of the design element 

implemented (or not implemented). For example, a lack of appreciation for the intended 

continuity of airflow control at the parapet led to: 

•	 Installation of a transition membrane at the parapet that did not transition the airflow 

control (Figure 30) 

•	 Sequence of wood framing installation that precluded transition of airflow control
 

(Figure 27).
 

A lack of appreciation for the drainage functions of the water and air control membrane and of 

the drainage cavity behind the cladding appears to have been a factor in: 

•	 Details implemented in a way that concentrates moisture at openings (Figure 45) 

•	 Installation of framing against the masonry and (initially at one site) strapping in a 

horizontal orientation (Figure 19, Figure 21, and Figure 25). 

The fact that the contractors did not appreciate the need for a continuous water and air control at 

the face of the masonry or the need to ensure effective transition of these control functions is 

likely to have contributed to: 

•	 Sequencing that precluded continuity of the control function around windows (Figure 14) 

•	 The presence of gaps in the water and air control membrane at window openings
 

(Figure 16 and Figure 17).
 

A misunderstanding of the risks intended to be managed by the screening at the base of the wall 

assembly led to: 

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•	 Sequencing that precluded effective protection at base of assembly (Figure 32) 

•	 Screening installed at the base of the assembly that fails to protect the exposed edge of 

the insulating sheathing (Figure 62). 

Figure 62. Screening at the base of the wall that fails to protect the exposed edge of the insulating 

sheathing near grade 

(Credit: Scott Sanders, CEDA) 

After completing substantial portions of the construction, both contractors were asked about 

potential cost savings that might be realized in future applications of the exterior insulation and 

over-cladding approach. Both suggested that eliminating the elastomeric paint layer would result 

in substantial cost savings. This demonstrates that, even after having implemented substantial 

portions of the exterior retrofit, the contractors did not appreciate the need for airflow and water 

control at the face of the masonry. 

In order to engage the skill and resourcefulness of the contractors and crews in fulfillment of the 

design intentions, it is necessary to establish an understanding of the functional design intentions. 

A three-part process is proposed for establishing understanding of the functional design intent: 

1.	 The functional intent of elements within an assembly or detail should be explicitly noted 

in construction drawings. 

2.	 The designer and contractor should review the rationale for the functional intent (e.g., 

water control) called out in the drawings. This will serve to develop an appreciation for 

the need for various functions in the design (e.g., airflow control, pest control) and tap the 

resourcefulness of the contractor, who might be able to suggest alternative methods for 

meeting the same intent. 

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3.	 The construction contract and schedule should allow for in-situ mockups of critical 

details. In-situ mockups are valuable in communicating functional requirements to crews 

and provide an opportunity to evaluate whether conditions of the building require 

refinements to details in order to achieve the functional intent. Mockups are also 

extremely valuable in providing contractors and crews the opportunity to develop 

confidence with unfamiliar systems or approaches. 

8.5.2 Specific Practice Recommendations 

The experience of the two implementations of the exterior insulation and over-cladding strategy 

yields specific recommendations that would benefit contractors involved in future 

implementations of the strategy. 

•	 Remove any obstructions that can be removed from the wall surface prior to application 

of the water and air control membrane at the face of the masonry. It is best to apply the 

water and air control membrane at the field of the wall in one uninterrupted step so that 

subsequent steps do not inhibit continuity of the control membrane. 

•	 When installing the water and airflow control membrane at the face of the masonry, treat 

penetration, opening, and obstruction details separately from the field of the wall. This 

allows for greater attention to areas that require it and allows for application in the field 

of the wall to proceed more rapidly. It is worth noting that details around penetrations, 

openings, and obstructions and may require different materials and methods than the field 

of the wall. 

•	 Because the need to terminate self-adhered peel-and-stick type flashings is not well 

understood or received, consider using liquid-applied flashing at critical details. 

•	 Ensure the trim returns slope away from openings and that the trim returns above
 

openings include a provision for drainage.
 

•	 Ensure that flashing is properly lapped and slopes away from the building. 

•	 Avoid installation of framing against the masonry or strapping over the insulating 

sheathing in a horizontal orientation.
 

•	 Anticipate imperfections or “character” in the masonry walls of older buildings. The 

exterior insulation and over-cladding assembly should be able to conform to wall surfaces 

that are slightly out of flat. More noticeable imperfections at the masonry can be flattened 

by the use of sloped insulation boards or thickened strapping carefully scribed and resawn to provide a flat attachment surface for cladding. Methods used to address 

imperfections in the wall should avoid creating large air gaps in the insulation layer. 

•	 Plan remediation of the parapet. Experience and observation have shown that many 

parapets are commonly not in good repair. It may be possible to use over-cladding as a 

means to re-establish the parapet height if the masonry is deteriorated at the top. 

•	 Anticipate variability of existing building dimensions by providing insulation material at 

various thicknesses for critical details such as window surrounds. 

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•	 Plan to provide protection for the base of the assembly. Attach screening to the base of 

the existing masonry wall before installing wood framing and insulating sheathing. Or, 

use a closure piece that permits drainage, slopes toward the front of the wall, provides 

ventilation openings, and is bedded in sealant against the existing masonry. 

•	 If using large-sized panel cladding (as distinct from lapped cladding), design and plan 

joints to coordinate with building elements. Consider designed joints, reveals, or battens. 

•	 Provisionally attach insulating sheathing with screws and washers to allow continuous 

taping of seams. 

•	 Use a starter strip of insulating sheathing at the base of the wall to provide an offset of 12 

in. or more between horizontal joints. 

8.6	 What are successful strategies to integrate windows into a masonry wall 

insulation and cladding retrofit system? 

At window openings, it is critical to provide robust water control and effective transition of both 

the airflow and thermal control to the window unit. 

In the ideal retrofit circumstances, windows would be removed to allow flashing of the window 

opening. Proper flashing of the window opening would include a pan flashing to direct water 

leaking through or around the window back out over the cladding or to the drainage cavity 

behind the cladding. The sill pan flashing as well as flashing at jambs of the window opening 

would be integrated with the air control membrane at the face of the masonry. These jamb and 

sill flashings would then double as transition membranes for the airflow control. A dedicated 

airflow control transition membrane would be needed at the head of the window to transition the 

airflow control into the window opening. With the airflow control transitioned into the window 

opening, the window is then sealed to these transition membranes around the inside perimeter of 

the window frame to connect the window in an airtight manner to the airflow control of the wall 

system. Joints at the head and jamb of the window would be sealed at the outer face of the 

window frame to prevent water entry, whereas the joint between the bottom of the window frame 

and the sill flashing would be left open or provided with weeps to allow drainage. 

Notwithstanding the ideal nature of this flashed window opening scenario, many retrofit 

situations, including the two projects evaluated in this study, present a different reality wherein 

the existing windows are to remain in place. Retaining the existing windows presents some 

challenges to providing effective water control and airflow control at the window openings. 

Where the windows are not provided with pan flashing beneath them, the approach for 

integrating the window with the water control function of the wall system is essentially a facesealing approach. In this approach, the water control membrane of the wall system is brought to 

and seals to the face of the window frame on all four sides. Care must be exercised not to cover 

any weep holes in the window frame. This approach establishes the water control at the face of 

the window unit and provides for drainage through weep holes in the window frame of small 

amounts of water that might leak between the sash and the window frame. This approach does 

not have provisions to directly manage water that leaks through or around the window frame. 

The face-sealed approach to water control at window openings relies upon either or both of the 

following conditions: 

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• Windows do not leak. 

•	 Where windows do leak, they leak to where the wall system can safely store and manage 

the amount of water leaking. 

Brick masonry wall assemblies may have some capacity to safely store water. However, the 

exterior insulation and over-cladding strategy will virtually eliminate the ability of the masonry 

to dry to the outside. Thus, the balance between safe storage capacity and drying could be 

disrupted by application of the exterior retrofit assembly. 

The strategy to manage risks of an existing face-sealed window includes directing water away 

from the window opening as much as possible, protecting joints between the window frame and 

surrounding assemblies, and finally, providing details that facilitate removal of the existing 

window for repair or replacement. 

The membrane applied to the face of the masonry is the primary water and air control layer for 

the system. Both functions are performed by the same material as it wraps into openings and 

seals to the window frame. Because the details around a window opening create many corners, 

gaps, and irregular surfaces, the area around a window requires a more robust water and air 

control membrane than is applied in the field of the wall. For example, an elastomeric paint 

might be recommended as the water and air control membrane for the field of the wall, but a 

liquid-applied flashing would be more appropriate for window openings (and other challenging 

details). Unlike sheet membranes, liquid-applied membranes conform well to inside corners, thus 

avoiding gaps in the airflow control function. Liquid-applied membranes will require substrate 

support to bridge small gaps and cracks. 

A sheet flashing will be needed to extend over the insulating sheathing of the wall and direct 

water out over the face of the cladding or to the drainage cavity behind the cladding. The top 

edge of the sheet flashing (at sill and jambs) must be integrated with the air/water control 

membrane in the window opening.9 

When the window opening is prepared in this way, subsequent reinstallation or replacement of 

the window could provide flashing for a drained opening (as described in Section 6) that readily 

integrates with the water and airflow control established for the face-sealed window. 

Because masonry is generally highly conductive, it is important to insulate the returns at the 

window opening. The thickness of the insulation should be maximize to the extent practical 

while not obstructing view, inhibiting operation of the window, or causing the weep holes of the 

frame to be below the sill trim. Coil stock trim returns allow a greater thickness of insulation to 

be accommodated at the window opening returns. The thickness of insulation that can be 

accommodated at the window opening may not be consistent across all window openings of the 

building. The implementation should aim to achieve at least R-5 continuous insulation over the 

window returns. 

In order to protect the water and airflow control joint at surrounding the window frame, the 

insulation returns and trim should butt into the window frame with a sealant joint between the 

trim returns and window frame. Because the head return trim intercepts water draining from 

9 This same approach to the flashing at the sill and base of the jambs would be employed in cases where the existing 

window opening did include a sill pan flashing. 

103
 
 

 

 

 

 

 

 

 

 

 

	 

	 

	 

	 

	 

	 


 

	 

	 

	 

	 


 

above the window, it must be sloped to the outside (away from the window) and have provision 

to drain water at the front edge. If the window sill does not offer a positive slope to the outside or 

if the slope is weak, the sill trim should be shimmed to provide an adequate slope to direct water 

at the face of the cladding and trim away from the window. 

In summary, the recommended strategies for integrating windows into a masonry wall insulation 

and cladding retrofit system are: 

•	 Use a robust water and air control membrane such as a liquid applied flashing, at window 

openings. 

•	 Apply water and air control at window openings separately from the water/air control 

membrane on the wall to permit attention to detail at window openings and rapid 

application in the field of the wall. 

•	 Extend the water and air control membrane onto the window frame and seal to the 

window frame, but ensure that weep holes in the window frame are not obstructed by the 

water and air control membrane. The weep holes for the window frame should also be 

above the sill trim. 

•	 Use a sheet membrane to extend the window sill flashing out over the face of the 

cladding or to the drainage cavity behind the cladding. Integrate the top edge of the sheet 

flashing with the water and air control membrane at the sill and jambs in an air/watertight 

flexible and durable manner. 

•	 Insulate the returns of the window opening to a minimum of R-5. Provide insulation 

material at various thicknesses to accommodate variations between windows. 

•	 Use coil stock trim returns to maximize the thickness of insulation that can be 

accommodated at window returns.
 

•	 Protect the joint between the window frame and the surrounding material/assembly by 

butting the insulation and trim returns into the window frame. Seal the trim to the 

window frame. 

•	 Ensure that the head trim return slopes away from the window opening and has drainage 

holes at the front edge (away from the window). 

•	 Where the slope of existing sill is weak, shim sill the trim to provide adequate slope away 

from the window. 

•	 Install removable casing trim around window openings to allow future work on the 

window openings without requiring removal of—or causing damage to—cladding 

surrounding the window. 

104
 
 

 

 

 

 

 

 

 

 

 

 


 

9 Looking Forward 

9.1 Gaps 

Observations and analysis conducted through the course of this research identified several 

development gaps that impact the feasibility of providing high performance exterior insulation 

and over-cladding. These are outlined below. 

9.1.1 Costs 

Even with the implemented strategy representing a significant decrease in annualized energyrelated costs, the significant financial outlay required to implement the strategy is likely to 

represent a barrier to both homeowners and energy efficiency programs. The cost for the 

measures may decrease if contractors become more familiar with the measure. The process for 

implementation of the strategy at the larger building provides on indication that costs would 

decline after further iteration of the strategy by contractors. The contractor for this building 

completed the treatment of one wall of the building in approximately three weeks. 

Implementation at the second wall of the building (which was essentially the same size as the 

first) took this contractor less than one week. 

9.1.2 Aesthetic Coordination 

The over-cladding of a building has the potential to improve the appearance of the building. 

Over-cladding might even be employed to produce a creative visual expression of the building. 

Greater attention to the appearance of the insulation and over-cladding assembly is likely to 

increase the appeal of the approach. The increased appreciation for the aesthetic benefits of the 

exterior insulation and over-cladding can then be leveraged to promote broader adoption. 

9.1.3 Assembly Approvals Relative to Fire Safety 

Even when the existing building is of solid masonry construction, an exterior insulation and 

over-cladding assembly might attract concerns relative to fire safety. The expense of testing 

specific exterior insulation and over-cladding assemblies would almost certainly preclude 

implementation of these assemblies. Industry-accepted protocols for evaluating “equivalent risk” 

relative to fire safety (see Kuhn and Jeffrey 2012) would make it possible to develop and 

implement strategies adapted to individual buildings. 

9.1.4 Product Availability 

Another avenue to address the potential for fire safety concerns would be to use assemblies 

based on products that avoid fire safety concerns. An EIFS that uses mineral wool insulation 

rather than XPS would resolve one of the significant barriers to using EIFS systems for enclosure 

retrofit. At this time, mineral wool-based EIFS systems are not readily available in the United 

States. 

9.1.5 Appreciation for Maintenance 

The exterior insulation and over-cladding strategy studied in this research project has the 

potential to significantly reduce maintenance needs for masonry buildings. Where there is a 

general lack of appreciation for maintenance or for the need for building maintenance, there is 

little value represented in avoided maintenance. 

105
 
 

 

 

	 

	 

	 

	 

	 

	 


 

9.2 Directions for Further Research 

The current research project studied a particular strategy for retrofit of solid masonry structures 

within a fairly specific implementation context. Related strategies that merit further research 

include: 

•	 Exterior insulation and over-cladding assemblies employing closed-cell spray-applied 

insulation 

•	 Exterior insulation and finish systems employing noncombustible insulation material. 

Important details of exterior insulation and over-cladding that could be studied in other project 

contexts include: 

•	 Connections between exterior insulation and over-cladding assemblies and sloped roofs 

•	 Implementation of exterior insulation and over-cladding assemblies around attached 

obstructions such as fire escapes and decks supported on the masonry wall. 

Measured performance could provide a more certain demonstration of the strategy’s impact on 

building performance. Monitoring of energy use at each of these buildings would contribute 

toward this end. Other measurements would benefit from controlled and comprehensive 

implementations: 

•	 Thoroughly measure air leakage performance before and after implementation of the 

exterior insulation and over-cladding strategy and in the absence of other measures that 

might impact air leakage performance. 

•	 Record energy use data for an extended period before and after implementation of the 

exterior insulation and over-cladding strategy and in the absence of other measures that 

might impact energy use. 

As suggested above, additional iterations of the approach studied may reduce the measure cost. 

Studying a broader test implementation involving multiple implementations by contractors 

would provide an opportunity to project more mature market costs and persistent implementation 

challenges to the measure. 

Quantification of parameters related to nonenergy benefits such as, for example, improved 

comfort, could lead to increased perceptions of overall value represented by the exterior 

insulation and over-cladding approach. 

106
 
 

 

 

 

 

 


 

References 

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2013 

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Lstiburek, J.W. (2008). BSI-005: A Bridge Too Far. Somerville, MA: Building Science 

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Morelli, M. (2010). “Internal Insulation of Masonry Walls with Wooden Floor Beams in 

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Neuhauser, K. (2012). RR-1205: Attic or Roof? An Evaluation of Two Advanced Weatherization 

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Years.” High Performing Buildings 2, Spring 2009. 

Straube, J.F.; Schumacher, C.J. (2002). Comparison of Monitored and Modeled Envelope 

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Straube, J.F.; Schumacher, C.J.; Ueno, K. (2012). RR-1105: Internal Insulation of Masonry 

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Straube, J.F.; Smegal, J. (2009) “Building America Special Research Project—High-R Walls 

Case Study Analysis.” RR-0903. Buildingscience.com 

Ueno, K. (2010). “Residential Exterior Wall Superinsulation Retrofit Details and Analysis.” 

Performance of the Exterior Envelopes of Whole Buildings XI. Atlanta, GA: American Society 

of Heating, Refrigeration, and Air-Conditioning Engineers, Inc. 

Ueno, K. (2012). RR-1201: Masonry Wall Insulation Interior Embedded Beam Simulations. 

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www.buildingscience.com/documents/reports/rr-1201-masonry-wall-insulation-interiorembedded-beam-simulations/view. Accessed August 31, 2012. 

108
 

 

Appendix A: Schematic Details Incorporated Into Contractor Bid 

Packages 

109
 
81
82

 

Appendix B: Insulation and Over-Cladding Work Order for Larger 

Multifamily Building 

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