Spray Foam Exterior 

Insulation with Stand-Off 

Furring

Anastasia Herk, Richard Baker, and 

Duncan Prahl

IBACOS, Inc.

March 2014
NOTICE

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

government. Neither the United States government nor any agency thereof, nor any of their employees, 

subcontractors, or affiliated partners makes any warranty, express or implied, or assumes any legal 

liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, 

product, or process disclosed, or represents that its use would not infringe privately owned rights.

Reference herein to any specific commercial product, process, or service by trade name, trademark, 

manufacturer, or otherwise does not necessarily 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 United States government or any agency 

thereof.

Available electronically at www.osti.gov/scitech

Available for a processing fee to U.S. Department of Energy

and its contractors, in paper, from:

U.S. Department of Energy

Office of Scientific and Technical Information

P.O. Box 62

Oak Ridge, TN 37831-0062

phone: 865.576.8401

fax: 865.576.5728

email: mailto:reports@adonis.osti.gov

Available for sale to the public, in paper, from:

U.S. Department of Commerce

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

phone: 800.553.6847

fax: 703.605.6900

email: orders@ntis.fedworld.gov

online ordering: www.ntis.gov/ordering.htm

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste
iii

Spray Foam Exterior Insulation with Stand-Off Furring

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: 

Anastasia Herk, Richard Baker, and Duncan Prahl

IBACOS, Inc.

2214 Liberty Avenue

Pittsburgh, PA 15222

NREL Technical Monitor: Michael Gestwick

Prepared under Subcontract No. KNDJ-0-40341-04

March 2014
iv

Acknowledgments

IBACOS wishes to acknowledge the New York State Research and Development Authority, 

GreenHomes America, Bayer MaterialScience, Simpson Strong-Tie Company, Inc., and the 

homeowner for co-funding this work. This report was prepared for the U.S. Department of 

Energy Building America program. Funding for this work was also provided by the National 

Renewable Energy Laboratory.
v

Contents

Acknowledgments ..................................................................................................................................... iv

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

List of Tables ............................................................................................................................................ viii

Definitions................................................................................................................................................... ix

Executive Summary.................................................................................................................................... x

1 Introduction and Background ............................................................................................................. 1

1.1 Statement of the Problem.....................................................................................................1

1.1.1 What Is a Deep Energy Retrofit? .............................................................................2

1.2 Key Research Questions......................................................................................................2

1.3 Performance Targets............................................................................................................2

2 Mathematical and Modeling Methods................................................................................................. 3

2.1 Modeling..............................................................................................................................3

2.2 Construction Detail Development........................................................................................4

3 Research and Experimental Methods ................................................................................................ 7

3.1 Planning ...............................................................................................................................7

3.2 Design Detailing ..................................................................................................................7

3.3 Energy and Structural Analyses...........................................................................................7

3.4 Mockups...............................................................................................................................7

3.5 Implementation ....................................................................................................................7

3.5.1 Homeowner Acquisition Strategy............................................................................7

3.5.2 Overview of Existing Conditions and Energy Analysis..........................................7

3.5.3 Development of Work Scope...................................................................................8

3.6 Permitting.............................................................................................................................8

3.7 Construction.........................................................................................................................8

4 Results................................................................................................................................................... 9

4.1 Planning ...............................................................................................................................9

4.2 Design Detailing ..................................................................................................................9

4.3 Structural and Energy Analyses.........................................................................................10

4.4 Mockups.............................................................................................................................12

4.5 Implementation ..................................................................................................................13

4.5.1 Homeowner Acquisition Strategy..........................................................................13

4.5.2 Overview of Existing Conditions...........................................................................14

4.5.3 Development of the Work Scope...........................................................................17

4.6 Permitting...........................................................................................................................18

4.7 House Construction............................................................................................................18

4.7.1 Material List...........................................................................................................19

4.7.2 Construction Schedule ...........................................................................................19

4.7.3 Construction Process..............................................................................................19

4.8 Costing ...............................................................................................................................25

4.9 Testing Results...................................................................................................................25

5 Discussion........................................................................................................................................... 27

5.1 Construction Results..........................................................................................................27

5.2 Construction Issues............................................................................................................27

5.2.1 Installation of Ledger Boards.................................................................................27

5.2.2 Brackets and Spray Foam ......................................................................................28

5.2.3 Window Installation...............................................................................................29
vi

5.3 Before and After Details....................................................................................................30

5.4 House Airtightness Results................................................................................................32

5.5 Monitoring .........................................................................................................................32

6 Conclusions ........................................................................................................................................ 33

7 References .......................................................................................................................................... 34

Appendix A: Description .......................................................................................................................... 35

Appendix B: Computer-Aided Design Details........................................................................................ 51

Appendix C: Additional Mockups............................................................................................................ 56

Appendix D: Compliance.......................................................................................................................... 59
vii

List of Figures

Figure 1. BEopt results without rebates and financing .......................................................................... 3

Figure 2. BEopt results with rebates and financing ................................................................................ 3

Figure 3. Results of financial analysis...................................................................................................... 4

Figure 4. Wall section ................................................................................................................................. 5

Figure 5. Bottom of wall section................................................................................................................ 6

Figure 6. Wall-at-foundation detail .......................................................................................................... 10

Figure 7. Simpson Strong-Tie “L” bracket ............................................................................................. 11

Figure 8. Structural calculation ............................................................................................................... 11

Figure 9. Detail around exterior door and light fixture.......................................................................... 13

Figure 10. Home screening worksheet excerpt ..................................................................................... 14

Figure 11. Preliminary sketch of the test house floor plan................................................................... 15

Figure 12. Front door of the test house .................................................................................................. 16

Figure 13. Side view of the test house.................................................................................................... 16

Figure 14. Energy assessment example................................................................................................. 17

Figure 15. Work scope example .............................................................................................................. 18

Figure 16. Construction schedule with exterior wall timing highlighted ............................................ 19

Figure 17. Exterior framing ...................................................................................................................... 20

Figure 18. Exterior front framing ............................................................................................................. 20

Figure 19. Installation of spray foam ...................................................................................................... 21

Figure 20. Window detail at built-out box............................................................................................... 21

Figure 21. Window detail.......................................................................................................................... 22

Figure 22. Exterior spray overview ......................................................................................................... 22

Figure 23. DER intersection ..................................................................................................................... 23

Figure 24. Exterior thin profile sheathing............................................................................................... 23

Figure 25. Siding Installation ................................................................................................................... 24

Figure 26. Insect guard and ventilation at the bottom of the wall system .......................................... 24

Figure 27. Final exterior front of the test house .................................................................................... 25

Figure 28. Installation of ledger boards.................................................................................................. 28

Figure 29. Brackets on top and bottom .................................................................................................. 29

Figure 30. Window installation ................................................................................................................ 30

Figure 31. Before—Bottom-of-wall details ............................................................................................. 30

Figure 32. After—Bottom-of-wall details ................................................................................................ 31

Figure 33. Before—Top-of-wall details ................................................................................................... 31

Figure 34. After—Top-of-wall details ...................................................................................................... 32

Figure 35. Step 1: Assess the existing condition of the wall. .............................................................. 36

Figure 36. Step 2: Remove the existing window trim, and fasten the ledger boards through the 

existing exterior cladding and sheathing. ....................................................................................... 37

Figure 37. Step 3: Attach the metal “L” clips on the top and bottom ledger board—one on 

either side of where the new vertical 2 × 4 will be attached. Also in Step 3, remove the 

existing window, and install new framing for the new window. .................................................... 38

Figure 38. Step 4: Install the vertical 2 × 4s, spaced as needed based on structural 

calculations and siding manufacturer requirements...................................................................... 39

Figure 39. Step 5: Install two horizontal framing members on the top and bottom of the rough 

opening for the new window. Slightly slope the sill framing to the exterior................................ 40

Figure 40. Step 6: Install the sill pan....................................................................................................... 41

Figure 41. Step 7: Install the flexible flashing on the rough opening and at least 6 in. up the 

sides of the jamb. ............................................................................................................................... 42

Figure 42. Step 8: Install caulk on the face of the rough opening at the jambs and head. Do not 

caulk the sill. ....................................................................................................................................... 43

Figure 43. Step 9: Install the new window.............................................................................................. 44

Figure 44. Step 10: Install the jamb flashing (flat on the face of the window flange). ....................... 45
viii

Figure 45. Step 11: Install the head flashing from the face of the existing wall to lap over the 

head of the new window. Also, tape the flashing at the head using straight flashing tape 

lapped over the horizontal part of the head framing. ..................................................................... 46

Figure 46. Step 12: Install the vertical framing members above and below the new window, 

and install the insect screen to the bottom of the new wall. Air seal the window from the 

interior using non-expanding foam sealant, and install internal jamb extensions to 

prevent exterior spray foam from getting into the house. ............................................................. 47

Figure 47. Step 13: Begin the spray foaming by first spraying the foam around the edges of 

the vertical 2 × 4s to “picture frame” the area. This will also allow the spray foam to extend 

under the 2 × 4 being held off the existing wall by the clips. Secure the framing in place to 

minimize movement of the studs...................................................................................................... 48

Figure 48. Step 14: Spray insulation within cavities of the new wall. ................................................. 49

Figure 49. Step 15: Install the new cladding, and install the new window trim.................................. 50

Figure 50. Wall at foundation................................................................................................................... 51

Figure 51. Roof to wall.............................................................................................................................. 52

Figure 52. Wall at floor.............................................................................................................................. 52

Figure 53. Window details........................................................................................................................ 53

Figure 54. Wall to roof .............................................................................................................................. 53

Figure 55. Flush rake ................................................................................................................................ 54

Figure 56. Shed roof ................................................................................................................................. 54

Figure 57. Tear-away view of wall construction..................................................................................... 55

Figure 58. Tear-away view of wall construction from the other side................................................... 55

Figure 59. Detail around exterior door and light fixture........................................................................ 56

Figure 60. Detail around band joist ......................................................................................................... 57

Figure 61. Detail at second-floor roof ..................................................................................................... 57

Figure 62. Detail at inverted corner and light fixture............................................................................. 58

Unless otherwise noted, all figures and photos were created by IBACOS.

List of Tables

Table 1. Financing Variables Studied ....................................................................................................... 3

Table 2. Wall Cost Estimates Versus Actual Cost................................................................................. 25

Table 3. Test House Airflow Reduction by Stage, Without the Basement .......................................... 26

Unless otherwise noted, all tables were created by IBACOS.
ix

Definitions

ASD Allowable strength design

BEoptTM Building Energy Optimization (software)

DER Deep energy retrofit

GHA GreenHomes America

HVAC Heating, ventilation, and air conditioning

NDS National Design Specification

NYSERDA New York State Energy Research and Development Authority

SSF Shell square foot

TREAT Targeted Retrofit Energy Analysis Tool
x

Executive Summary

IBACOS and GreenHomes America1 (GHA) collaborated with the New York State Energy 

Research and Development Authority (NYSERDA) Advanced Buildings Program to research a 

variation of a commercial curtain wall assembly for residential construction as part of a 

comprehensive whole-house deep energy retrofit (DER) package. The advantages of this strategy 

include minimizing the physical connections to each individual existing wall stud, using closedcell spray foam to encapsulate existing siding materials including lead paint, and creating a 

vented rain screen assembly to promote drying. As Moore (2011) states, “Closed-cell foam acts 

as air-sealing, insulation, and secondary drainage plane...” Field installations on a limited 

number of houses indicate that the incremental cost when installed as part of a typical siding and 

window replacement job adds approximately $10/ft2 of wall area. 

2 × 4 framing members were attached to the wall at band joists and top plates using “L” clips, 

and spray foam was used to insulate the wall after the framing was installed. Windows were 

installed as the framing was put up, including extension jambs. 

Key lessons learned include the following: 

• The installed cost of the spray foam system was comparable to the installed cost of the 

rigid foam and furring strips.

• Spray foam should be applied in such a way that it locks the framing members in place 

before the remaining foam is installed in the field of the wall. The spray foam has a 

tendency to move the new wall framing as it expands. Best practice is to “picture frame” 

the wall framing with spray foam and then apply the spray foam in the field of each bay.

• Variations in the existing siding conditions must be accounted for when attaching the 

ledger boards and wall framing. A best practice is to uniformly shim the ledger boards off 

the walls so the new framing is a uniform distance from the ledger boards and the inside 

surface of the interior framing. This is important primarily for window and door 

installation and the associated extension jambs and trim. 

• From a sequencing perspective, it is advantageous to replace the windows at the same 

time as the exterior walls are being built. This requires a crew that can perform a number 

of different tasks (e.g., framing, flashing, window install, trim carpentry) and does not 

lend itself to subcontracting this approach piecemeal (e.g., framing subcontractor, 

window installer, drainage plane installer, trim carpenter).

• Application of the brackets and associated fastener screws was more time consuming 

than anticipated. 

• It is important for the spray foam contractor to perform all preparatory work, which in 

this case included placing plastic over the windows and exposed foundation to minimize 

or eliminate the possibility of damage due to overspray.

 1 GreenHomes America, Inc., www.greenhomesamerica.com/.
1

1 Introduction and Background

According to Harvard (2010), “Lower household mobility in the wake of the housing market 

crash could also mean that homeowners will focus on upgrades with longer paybacks, 

particularly energy-efficient retrofits.” That report also shows that homeowners are investing in 

new siding ($4.847 billion in 2009) and new windows and doors ($11.448 billion in 2009). The 

decisions to make these improvements frequently occur without consideration of energy 

improvement opportunities, and research is needed to determine what additional measures could 

be taken to improve the energy efficiency of the home and the impact of the various 

opportunities. Home retrofits have been targeted as an area of great potential for significant 

energy savings, employment opportunities, and market growth (Osser et al. 2011). Exterior 

insulation is one strategy for reducing energy use for heating and cooling while reducing 

potential moisture problems in walls.

The New York State Energy Research and Development Authority (NYSERDA) Advanced 

Buildings Program has proven the economic need for, and the significant energy-saving benefits 

of, residential retrofitting strategies based on its deep energy retrofit (DER) pilot project. 

However, the DER activities are cost prohibitive. When looking into this project, IBACOS 

researched existing work on exterior insulation and energy smart walls. According to Coldham 

(2010), “Owners of existing homes can take advantage of energy savings that will result from

construction upgrades.” Coldham talks about six proven ways to build these energy smart walls. 

NYSERDA’s Advanced Buildings Program research was conducted to investigate cost-effective 

DER solutions for improving the building shell exterior while achieving a cost-reduction goal, 

including reducing labor costs considerably, to reach a balanced, 50/50 split between material 

and labor. The strategy is designed to integrate with other home improvement projects such as 

siding or window replacement, with both energy and appraisal value attributes, so DER solutions

gain market acceptance.

IBACOS, in collaboration with GreenHomes America (GHA), was contracted by NYSERDA to 

research exterior wall insulation solutions. IBACOS researched past projects done, including 

work done by Moore (2011). In addition to the exterior wall insulation, the strategies included

energy upgrades where needed in the attic, mechanical and ventilation systems, and basement 

band joist, walls, and floors. 

1.1 Statement of the Problem

One aspect of exterior insulation is creating a new external system for siding attachment that 

transfers loads back to the structure of the building, meets siding manufacturers’ requirements, 

and complies with the 2012 International Residential Code (International Code Council 2012). 

This typically means attaching furring strips directly to each vertical stud. Locating and verifying 

that fasteners are actually in the studs of existing exterior walls can be time consuming and 

challenging for retrofit crews. 

Many existing homes may have exterior surfaces that contain lead paint. Alfano (2010) estimates 

that lead paint safe work practices can escalate the cost of exterior retrofits by thousands of 

dollars if significant whole-house containment systems are needed for siding with lead paint. 

One goal of this research was to develop a strategy that would minimize the disturbance of the 
2

siding and lead paint, thereby avoiding triggering the thresholds for the U.S. Environmental 

Protection Agency’s Lead-Based Paint Renovation, Repair, and Painting Rule.

2

1.1.1 What Is a Deep Energy Retrofit?

A DER is a practice that goes well above and beyond the current common practice of performing 

energy efficiency work. This involves substantially improving the exterior building envelope 

with aggressive, emerging insulating practices (e.g., installing polyurethane rigid panel 

insulation, application of polyurethane spray foam insulation after build-out), installing new 

windows or relocating existing windows (when applicable), sealing the below-grade foundation 

to the wall connections, and sealing the roof-to-wall connection with insulation that also provides 

an air barrier. Typical mechanical systems are then significantly downsized, and performance 

results yield a reduction in whole-building energy load of at least 50%. 

1.2 Key Research Questions

The key research question for this project asks how exterior walls can be retrofitted with exterior 

insulation that accomplishes all of the following:

• Minimizes the need for attachment to each individual vertical framing member.

• Minimizes or eliminates the need to remove existing siding.

• Maintains the structural and siding attachment requirements of manufacturers and the 

2012 International Residential Code (International Code Council 2012).

1.3 Performance Targets

As part of this project, a number of goals were developed, including the following:

• Provide testing measurements, utility impact (before and after), costs (labor and 

materials), construction time, standard specifications, and analysis for the exterior wall 

insulation strategy. 

• Achieve the following energy-related targets:

o Whole-house air leakage improvements that can approach or be lower than 

0.25 CFM 50/shell square foot (SSF) upon completion.

o Minimum center of wall R-value of R-25.

• Increase DER awareness among building contractors and homeowners.

• Identify exterior wall insulation retrofit strategies that can be accomplished for less than 

$10/SSF.

• Share successful solutions with building contractors and homeowners through a wide 

outreach program.

• Identify barriers to solutions that need to be addressed with future research or 

externalities under which nonviable solutions would be made viable (e.g., different utility 

costs, lower material costs).

 2 U.S. Environmental Protection Agency, www2.epa.gov/lead/lead-renovation-repair-and-painting-program-rules.
3

2 Mathematical and Modeling Methods

The information below shows the modeling that was done prior to the start of construction to 

verify IBACOS’ strategy and the probability of meeting the project goals.

2.1 Modeling

IBACOS used Building Energy Optimization (BEoptTM) software Version 2.0.0.4 (BEopt 2013) 

to model the current conditions of a single-story house located in the area of Syracuse, New 

York, and an optimization of reasonable retrofit options, including the exterior insulation system 

with costs as found by the research team. Figure 1 shows the BEopt model with no rebates or 

financing options, assuming a 7% loan for 5 years to finance the costs. Figure 2 shows BEopt 

results when the rebates available through NYSERDA (approximately 10% of the cost of 

qualifying measures, up to $3,000 and ~4% 15-year loan) were included. Note that the actual 

house as built included a heat recovery ventilation system that significantly increased costs with 

little savings. In addition, all of the most cost-effective points do not include ventilation, which is 

not necessarily a recommended practice when working to aggressively air seal a building. The 

house had an existing sealed combustion furnace, and a power vent was installed on a relatively 

new gas tank type water heater. No house combinations achieved more than 20% savings 

without the inclusion of the exterior insulation system.

Figure 1. BEopt results without rebates and 

financing

Figure 2. BEopt results with rebates and 

financing

It is also instructive to look at the impact of rebates and financing of this strategy. BEopt was run 

with a parametric analysis of financing options and measures, including various interest rates and 

rebates as shown in Table 1. Figure 3 shows the results of this analysis.

Table 1. Financing Variables Studied

Parameter Variable 

Interest Rate 4%, 5.5%, 7%

Term of Loan 5, 10, 15, and 30 years

Rebates $2,500, $3000 for entire project
4

Figure 3. Results of financial analysis

One conclusion is that for major DER investments, it is advisable to evaluate all financing

options, including a full-house refinance to a 30-year loan, if a neutral cash flow is the goal. In 

many cases, this upgrade is made as part of other overall home improvement activities such as 

re-siding for aesthetic reasons or replacing windows for comfort and functionality. By adding 

this energy upgrade strategy to a re-siding/window replacement project, the homeowners are 

further enhancing the value of their home by creating a continuous thermal enclosure, 

minimizing the risk of condensation on exterior walls, and creating a continuous ventilated rain 

screen. 

2.2 Construction Detail Development

IBACOS created a detailed wall section for a spray foam application DER solution, as shown in 

Figure 4 and Figure 5. Structural analysis was conducted on these details as described in 

Section 3.
5

Figure 4. Wall section
6

Figure 5. Bottom of wall section
7

3 Research and Experimental Methods

This research was conducted in conjunction with project partner GHA and a number of 

manufacturing partners. Methods included a strategic planning meeting, design detailing, 

structural and energy analyses, mockups, and implementation.

3.1 Planning

At the start of the project, IBACOS gathered various manufacturers that were interested in this 

project and its outcomes. IBACOS held a strategic planning meeting with all of these 

manufacturers, NYSERDA representatives, and GHA representatives.

3.2 Design Detailing

IBACOS then took the discussion results from the strategic planning meeting and started to flesh 

out the details. IBACOS created two- and three-dimensional details of the ideas formed in the 

strategic planning meeting, working to identify all problem areas.

3.3 Energy and Structural Analyses

Energy analysis was undertaken using BEopt (Version 2.0.0.4) and Targeted Retrofit Energy 

Analysis Tool (TREAT) software (TREAT 2013). Once the team detailed the solution for this 

spray foam DER, it was necessary to do some structural analysis of the system. IBACOS 

planned to have 2 × 4s on edges that were clipped to a ledger board at two locations. After 

designing that detail, IBACOS worked with one manufacturing partner who specializes in 

structural metal brackets for residential construction regarding that company’s clips and the 

structural capability of those clips. 

3.4 Mockups

IBACOS created SketchUp details (SketchUp 2013) that addressed possible problem areas of a 

potential home, as identified by the team. These mockup drawings then were built into actual 

physical mockups at the GHA office by the contractors who would be working on the actual 

homes. Then GHA was able to test how this work would be done before actually beginning the 

project in the field. 

3.5 Implementation

To implement the spray foam stand-off furring strategy, the team had to find a homeowner who 

met the criteria. Next, the team had to review the existing conditions of that home and then 

develop a work scope of what the team would do during construction at that home.

3.5.1 Homeowner Acquisition Strategy

First, GHA developed a market solicitation program to identify and enroll four homeowners for 

study participation, including meeting cost share requirements. Based on the outcomes of a 

strategic planning meeting, IBACOS undertook energy and financial modeling to refine project 

costs and energy benefits in conjunction with laboratory mockups.

3.5.2 Overview of Existing Conditions and Energy Analysis

After a homeowner was chosen for the project, the GHA team assessed the house to ensure that 

the existing conditions were not too far out of reach for the construction of the DER. This 
8

included verifying chimney locations; any protrusions; the heating, ventilation, and air 

conditioning (HVAC) system; and other initial observations. 

3.5.3 Development of Work Scope

Once the team determined that the house was a good candidate for the DER, a work scope was 

created. This work scope included all work that would be done at the house during construction. 

The homeowner agreed to this work scope prior to the start of construction.

3.6 Permitting

Before the team could begin construction, it had to obtain permits from the local authorities for 

the retrofit work on the test house. Some of the permitting officials had never seen an application 

similar to this one; therefore, they were hesitant to award the permits. 

3.7 Construction

Using the best solution sets from the laboratory mockups, GHA implemented the solution set in 

conjunction with a number of other whole-house retrofit measures. IBACOS and GHA 

collaborated with other project partners to evaluate in-field applications and modifications that 

were necessary to reduce costs where possible. GHA collected detailed labor activities and 

documented the learning curve as the project progressed. IBACOS conducted periodic field 

visits at key points during construction to identify technical and process barriers that could 

prevent a solution from meeting the desired results.
9

4 Results

The following information discusses the results of the strategic planning meeting, design 

detailing, structural and energy analyses, mockups, and implementation.

4.1 Planning

During the strategic planning meeting, the team identified key issues that could impact the 

implementation of the solution. These issues included the following:

• Structural analysis and permitting

• Sequencing of the job

• Integration of the wall system to other key assemblies such as the foundation, windows 

and doors, and roof.

4.2 Design Detailing

During the strategic planning meeting, ideas for detailing also were discussed. The team 

identified different areas of concern that might be encountered at any given home. Discussion 

topics covered the roof-to-wall detail, floor-to-wall detail, and basement detail, among others. 

After the strategic planning meeting, IBACOS worked with GHA to detail the spray foam 

solution and created details for construction. Figure 6 shows one of the details. See Appendix A 

for step-by-step diagrams and Appendix B for computer-aided design details. 
10

Figure 6. Wall-at-foundation detail

4.3 Structural and Energy Analyses

During the detailing phase, IBACOS discussed using a variety of different brackets for the top 

and bottom of the 2 × 4 that was installed vertically. To satisfy the building official, an

engineer’s stamp was needed on the details. For the engineer to stamp the details, technical 

specifications were needed. Due to the lack of technical information on the structural strength of 

the adhesion of foam to wood, the clips were needed. The team decided to use a standard “L” 

bracket product from a national supplier of structural metal clips and hangers. This bracket

originally was designed for use on light-commercial, steel-framed curtain wall construction. 

Figure 7 shows a picture of the Simpson Strong-Tie “L” bracket that was used. 
11

Figure 7. Simpson Strong-Tie “L” bracket

Calculations were done to ensure that the weight of the wall could be carried by the metal 

brackets. Figure 8 shows the beginning of these calculations. This figure is a moment diagram 

that shows evenly distributed dead loads on the 2 × 4 framing member. GHA then performed 

TREAT modeling for NYSERDA purposes.

Figure 8. Structural calculation

The analysis of the wall section and other relevant members was done using allowable strength 

design (ASD) equations from the 2012 National Design Specification (NDS) (American Wood 

Council 2012a) and the ASD/LRFD Manual for Engineered Wood Construction (American 

Wood Council 2012b). The following modes of failure were considered:

• Failure of new 2 × 4 wall framing in compression

• Failure of mechanical connection of ledger board to rim joist
12

• Failure of ledger board in shear

• Failure of ledger board in flexure

• Failure of mechanical connection of ledger board to metal bracket

• Failure of mechanical connection of metal bracket to stud

• Loads for each of the wall section parameters:

o Vinyl, fiber cement, and stucco siding 

o Windows approximately the same weight as stucco

• Analysis done with new exterior wall studs spaced at 16 in. and 24 in. on center.

4.4 Mockups

IBACOS developed drawings of small-scale mockups for proposed solutions that were tested for 

constructability, material utilization, and time motion studies. IBACOS worked with GHA and 

its installers to provide input on the development of the mockups, laboratory testing, and review 

of results. 

The construction of full-scale mockups of key features typical to many existing homes in the 

area of Syracuse, New York, was the primary mechanism to allow for tests of the 

constructability of the proposed strategies. These mockups helped in the determination of the 

amount of materials and labor needed to execute a given strategy. They also provided a venue for 

those responsible for executing these unconventional practices in the field to refine application 

methods and sequencing prior to arriving on the job site.

After these full-scale mockups were built, the team was able to troubleshoot specific areas and 

revise the details before arriving on site at the test house. Figure 9 is representative of the 

mockup drawings (left) and the corresponding physical mockup (right) built by GHA. Additional 

mockups are presented in Appendix C.
13

Figure 9. Detail around exterior door and light fixture

4.5 Implementation

Once the mockups were complete, the team needed to find a homeowner who matched the 

project criteria and was willing to have their home monitored for a year after completion of the 

retrofit. The following describes some of the ways the team transitioned to the implementation

phase. 

4.5.1 Homeowner Acquisition Strategy

The team developed a home screening worksheet that was intended to help assess the suitability 

and existing situation of the potential home. This home screening worksheet included the 

following:

• General customer information

• Interior information (e.g., windows, attic, basement) 

• Exterior information (e.g., siding, chimney, porch, deck, utilities, exterior lighting, 

landscape)

• Checklist of photographs to be taken.

Figure 10 shows an excerpt from the home screening worksheet.
14

Figure 10. Home screening worksheet excerpt

4.5.2 Overview of Existing Conditions

The test home for this NYSERDA DER project is in a residential neighborhood in Syracuse,

New York. Two occupants reside in this single-story, ranch-style home that was built in the 

1970s and has a finished floor area of approximately 2,067 ft2

. Figure 11 shows the exterior 

walls of the test house.
15

Figure 11. Preliminary sketch of the test house floor plan

Heating and cooling in the existing home were provided by a natural gas furnace with air 

conditioning, with a metal ductwork distribution system, and the home appeared to have no leaks 

in the roof. The interior of the home included double-hung windows, R-10 fiberglass insulation 

in the attic, recessed lighting, and fiberglass wall insulation. Also, a water heater located in the 

basement was vented improperly and had no direct vent provision. Some existing exterior 

conditions of the home included wide shingles of the shake variety with about 9 in. of exposure, 

no chimneys, and a small overhang at the front door, as well as some exterior lighting and a gas 

meter on the exterior. Figure 12 and Figure 13 show the test house.
16

Figure 12. Front door of the test house

Figure 13. Side view of the test house
17

4.5.2.1 Initial Home Energy Assessment

GHA conducted an energy assessment of the test house prior to doing any work on the home. 

This energy assessment included the following: 

• HVAC equipment (type, year installed, fuel type, location, and condition)

• Domestic hot water equipment (type, year installed, fuel type, location, and condition)

• Conditioned area and volume calculations

• Number of heated floors in the home

• Fan locations

• Dishwasher, clothes washer, and refrigerator (make and age of each).

Figure 14 shows an example of this energy assessment.

Figure 14. Energy assessment example

4.5.3 Development of the Work Scope

Once the existing conditions of the test house were assessed, a work scope was created. This 

work scope described all renovations and updates to be done at this residence. The test house 

was to receive a spray foam strategy, and the construction included the following: 

• Installation of whole-house vinyl siding in the Woodland Green color, 5-in. width 

• Installation of vinyl soffit material for overhangs
18

• Application of white trim to the fascia, 22 windows, two doors, and one garage door 

• Addition of a dryer vent in the Woodland Green color

• Installation of 3⁄8-in. sheathing over insulation for a flat surface under the siding.

Figure 15 shows an example of the work scope for the test house.

Figure 15. Work scope example

4.6 Permitting

The code official in the area in which the test home was located had never seen this type of DER. 

He wanted to be sure this construction was safe and therefore asked for a professional stamp on 

the details, structural calculations, and related materials. In response to this request, IBACOS 

assembled a package that included the construction drawings for the DER, structural 

calculations, and a summary letter of how the construction would be executed. IBACOS then 

collaborated with a licensed structural engineer in New York, who agreed to stamp the package. 

This stamped package was sent to the code official, and construction was approved to 

commence. 

Appendix D discusses some of the questions that might have to be addressed to acquire a permit

before construction of a stand-off furring project can begin. 

4.7 House Construction

Using the best solution sets from the laboratory mockups, GHA implemented the chosen 

solution. IBACOS and GHA worked together with other project partners to evaluate in-field 

applications and modifications that were necessary to reduce costs where possible. GHA worked 

to collect detailed labor activities and documented the learning curve in actual field practices 
19

compared to the mockups. GHA used the same construction crew for the retrofit to document the 

progression of knowledge and to identify training needs that could speed adoption. IBACOS 

conducted periodic field visits at key points during construction to identify technical and process 

barriers that could prevent a solution from meeting the desired results.

4.7.1 Material List

Materials used and unit costs per square foot for the exterior wall system were determined before 

construction. This helped to inform the overall cost of the system. 

4.7.2 Construction Schedule

GHA created the project schedule, as shown in Figure 16, based on its prior knowledge of energy 

upgrades to homes. During Week 1 of the project, GHA prepared for the construction by 

ordering materials, obtaining permits, and notifying manufacturers of the timeline. During Week

2, the subcontractors began to install some mechanical equipment and start the energy upgrades 

to the attic and basement. During Week 3, the exterior framing of the wall system commenced. 

In Week 4, the subcontractors installed the windows and doors and added the spray foam 

insulation to the exteiror wall. This was followed in Week 5 by the addition of new siding on top 

of the wall system.

Figure 16. Construction schedule with exterior wall timing highlighted

4.7.3 Construction Process

The following section of photographs provides a visual record of the progress of construction on 

the test house. Step-by-step details are included in Appendix A.
20 

Figure 17 shows the start of framing being installed over the existing siding for the spray foam 

DER.

Figure 17. Exterior framing

Figure 18 shows the front elevation of the house, with most of the framework installed. 

Figure 18. Exterior front framing
21 

The house then was ready for the application of the spray foam. Figure 19 shows the start of that 

process.

Figure 19. Installation of spray foam 

Figure 20 shows the interior unfinished build-out after the new window was installed. 

Figure 20. Window detail at built-out box
22

Figure 21 shows the interior finished wall trim after the new window was installed.

Figure 21. Window detail

Figure 22 shows the exterior of the test house with the spray foam in place.

Figure 22. Exterior spray overview
23

Figure 23 shows the wall system at interior and exterior corners.

Figure 23. DER intersection

Because this house was to receive new vinyl siding, a sheathing product was needed over the 

studs, per the vinyl siding manufacturer’s recommendation. The team used a thin profile 

structural sheathing that was extended to the roof line and was installed after the spray foam

insulation. Bulk water was handled by the thin profile sheathing, and it was inferred that 

incidental water past the sheathing would drain over the spray foam. Figure 24 shows the thin 

profile sheathing being attached.

Figure 24. Exterior thin profile sheathing
24

Figure 25 shows the installed thin profile sheathing with the vinyl siding. Note that taping of the 

windows and seams in the sheathing provides an extra layer of water management in addition to 

those shown in the step-by-step details described in Appendix A. 

Figure 25. Siding Installation

Figure 26 shows the insect screening that was installed at the bottom of the new siding 

application.

Figure 26. Insect guard and ventilation at the bottom of the wall system
25

Finally, Figure 27 shows the front elevation of the home after construction was complete.

Figure 27. Final exterior front of the test house

4.8 Costing

One of the main research questions in this DER project was to find a way to install exterior 

insulation systems for $10/ft2 or less. Prior to construction, it was estimated that the cost per SSF 

would be $17, including siding. Table 2 shows a breakdown of the cost for the wall system. The 

wall work is broken down into the following categories: new framing, removal of existing 

windows, window trim, spray foam application, installation of thin profile sheathing, and 

installation of insect screen. The table also shows that, excluding the cost of the siding, the 

overall cost per square foot is slightly over the $10 target. 

Table 2. Wall Cost Estimates Versus Actual Cost

Wall Work Total Actual Actual Cost per SSF

New Framing $5,625 $2.57

Removal of Windows $671 $0.31

Window Trim $3,606 $1.65

Spray Foam $7,198 $3.29

Thin Profile Sheathing $3,717 $1.70

Insect Screen $1,167 $0.53

Total Without Siding $23,518 $10.76

Install Siding $18,574 $8.50

Total With Siding $42,093 $19.26

4.9 Testing Results

Blower door testing was conducted on the test house prior to construction, throughout 

construction, and at the completion of construction. Two different blower door tests were 
26

performed on the test house: one test that included the basement in the volume of the building,

and one that did not. 

Table 3 describes the blower door test results without including the basement in the volume of 

the building. The details used for the test house without including the basement are as follows: 

• Volume: 18,208 ft2

• Square feet of conditioned space: 2,276 ft2

• Perimeter of the house: 257 ft

• Wall height: 8 ft

• Shell square footage: 6,608 SSF.

Table 3. Test House Airflow Reduction by Stage, Without the Basement

Improvement 

Stage CFM50

CFM50 

Reduction 

From Start 

% 

Reduction 

From Start 

ACH50 CFM50/

SSF

Start 2,675 0 0% 8.8 0.40

Air Seal Attic 1,925 750 28% 6.3 0.29

Wall Build-Out (Including 

Windows and Foam) 1,800 875 33% 5.9 0.27

Spray Foam Band 

Joist/Energy Recovery 

Ventilator Installed

1,625 1,050 39% 5.4 0.25
27

5 Discussion

The following information describes the construction process and how it affected the outcomes 

of this project. 

5.1 Construction Results

Throughout the DER construction of the test house, IBACOS and GHA kept tabs on any 

unexpected issues that arose. The construction results are as follows: 

• The ledger boards installed over the existing siding were different distances from the 

existing plumb frame walls. This created additional layout work when installing the new 

studs to ensure the rough openings around windows and doors were a uniform dimension.

One solution would be to uniformly shim the ledger boards to be the same distance from 

the existing face of the wall framing.

• The brackets did not provide the initial rigidity expected for the new wall framing, and 

the studs moved more than expected when the spray foam was installed. “Picture 

framing” the studs with spray foam would likely secure them in place and minimize 

movement of the framing as the spray foam in the field of the wall is applied. 

• It had been decided that the windows would be installed after the exterior walls were 

built; however, it worked better to pull and replace the windows at the same time as the 

exterior walls were being built. 

• The metal brackets required many screws; application of these brackets and screws was 

more time consuming than anticipated. 

• Some siding was removed in areas where the roof line would not accept the new DER.

• Spray foam preparatory work included placing plastic over the windows and exposed 

foundation to protect them from overspray. 

5.2 Construction Issues

The following describes issues that arose when construction began on the test house. 

5.2.1 Installation of Ledger Boards

When the ledger boards were installed over existing siding, the inconsistent surface created more 

layout work. The distance of the ledger boards from the walls varied, depending on where these 

ledger boards fell. In the case of the test house, the siding was a wide shingle that left significant 

variation. This led to creating a new wall surface that did not follow the existing wall and rough 

opening. Figure 28 shows the installers measuring the surface and installing the 2 × 4 boards. 

In the future, this issue could be resolved by planning for the inconsistencies from the beginning 

and measuring out how far the boards need to be placed from the existing wall, or shimming the 

ledger to a consistent distance from the existing wall framing. 
28

Figure 28. Installation of ledger boards

5.2.2 Brackets and Spray Foam

There was a side-to-side bowing of the vertical studs, so it may be necessary to have a bracket at 

the midpoint of the wall. This can be a less expensive, nonstructural bracket that would simply 

provide the rigidity needed while spraying the insulation. This deflection caused additional 

“detail” work in installing the windows. Some rough openings were moved out of plumb, which 

affected the trim work and, in turn, affected timing. Figure 29 shows a close-up view of the two 

brackets at the top and bottom of the ledger boards. 

This issue could be resolved by using two or even three brackets from the start and strategically 

placing them for the greatest stability. 

When using spray foam, preparatory work is needed. For the test house, the preparatory work

included placing plastic over the windows and exposed foundation to protect them from 

overspray. However, the subcontractor also built a portable “tent” that propped against the house 

to minimize overspray onto plantings or other areas adjacent to the house.
29

Figure 29. Brackets on top and bottom

5.2.3 Window Installation

The decision to change the original plan of installing the windows after the exterior wall

construction to doing the two installations simultaneously allowed for sections of wall to be 

completed; however, this change left a gap between the old and new walls that had to be 

addressed. Instead of a temporary enclosure with tape or oriented strand board to handle foam 

expansion, it was decided to install the extension jambs along the way as well. This minimized 

disruptions on the inside as more work was done all at once in a particular area. Figure 30 shows 

this process. 

It is recommended that contractors plan for pulling and replacing the windows at the same time 

as the exterior wall framing is being built. 
30

Figure 30. Window installation

5.3 Before and After Details

Figure 31 through Figure 34 show the bottom- and top-of-wall details as the team began to plan 

them versus what developed into construction. 

Figure 31. Before—Bottom-of-wall details
31

Figure 32. After—Bottom-of-wall details

Figure 33. Before—Top-of-wall details
32

Figure 34. After—Top-of-wall details

All post-construction detail updates can be found in Appendix B.

5.4 House Airtightness Results

In Section 4, Table 3 showed that the wall system did not have a significant contribution to the 

overall airtightness improvement for the house compared to the attic air sealing. This may be due 

to the fact that the house was a single story with few possible exterior wall bypasses. 

5.5 Monitoring

The research team plans to install this strategy on a few other homes and to compare the use of 

rigid foam in place of the spray foam. On the house used in this stand-off furring project, 

monitoring will be done throughout the next year to determine the energy savings resulting from 

the DER. The monitoring will include indoor and outdoor temperature and relative humidity, run 

time of the space heating system, blower door tests, and collection of homeowner utility bills. 
33

6 Conclusions

Some lessons that were learned in the DER construction of this test house will help in future 

building for the contractor and for builders. 

Attention to the shimming of the ledger boards can help minimize downstream construction 

issues associated with the variation in exterior wall siding thicknesses. Additional supporting 

brackets or the strategic use of spray foam (i.e., “picture framing” the studs) to stabilize wall 

framing is needed to minimize framing movement due to the expansion of spray foam in the field 

of the wall.

Planning should include the installation of windows during the framing process. 

Prior to construction, it is important to assess the house to discover any potential problem areas. 

These problem areas could include the following:

• Areas where existing overhangs will not accommodate any added thickness of the wall 

system

• Services on the exterior of the house, such as plumbing, electrical, utility meters. and 

service entrances, and attachment to accessory structures such as decks

• Walls that continue from enclosing conditioned space to non-conditioned spaces, such as 

garages 

• Roof-to-wall intersections on two-story to single-story transitions.

The practice of conducting a stakeholder meeting—including all trades, the general contractor, 

the architect (if used), the homeowners, and any other individual who has influence on the 

project—should include a planning meeting prior to construction. All details should be discussed

and documented, all contractor questions should be answered, and any unforeseen circumstances 

should be brainstormed at the onset.

Finally, a clear lesson is that the homeowners always have an opinion on what will be installed in 

their home. Thus, it is best to be clear in the contract and to specify items for which the 

contractor is or is not responsible, as well as planning for homeowner design aesthetic issues. 
34

7 References

Alfano, S. (2010). How Much Will the RRP Cost? Remodeling Magazine, March 16, 

2010. www.remodeling.hw.net/lead-paint/how-much-will-the-rrp-cost.aspx.

American Wood Council (2012a). National Design Specification for Wood Construction, 2012 

ed. Leesburg, VA: American Wood Council. www.awc.org/standards/nds.html.

American Wood Council (2012b). ASD/LRFD Manual for Engineered Wood Construction. 2012 

ed. Leesburg, VA: American Wood Council. www.awc.org/standards/nds.html.

BEopt (2013). Building Energy Optimization with Hour-by-Hour Simulations, Version 2.0.0.4. 

Golden, CO: National Renewable Energy Laboratory. http://beopt.nrel.gov/.

Coldham, B. (2010). “Six Proven Ways to Build Energy-Smart Walls,” Fine Homebuilding 

Magazine, December 2009/January 2010. www.finehomebuilding.com/design/articles/sixproven-ways-to-build-energy-smart-walls.aspx?ac=fp.

Harvard (2010). A New Decade of Growth for Remodeling. Joint Center for Housing Studies of 

Harvard University. Cambridge, MA: Harvard University.

International Code Council (2012). International Residential Code for One- and Two-Family 

Dwellings. Country Club Hills, IL: International Code Council; Chapter 28.

Moore, T. (2011). “Insulating with Exterior Spray Foam,” Journal of Light Construction, May 

2011. www.jlconline.com/building-envelope/insulating-with-exterior-spray-foam.aspx.

Osser, R.; Neuhauser, K.; Ueno, K. (2011). “Final Retrofit Pilot Community Evaluation Report,”

BuildingScience.com, December 2011. www.buildingscience.com/documents/bareports/ba1107-final-retrofit-pilot-community-evaluation-report/view?topic=resources/retrofits.

SketchUp (2013). SketchUp software. www.sketchup.com/.

TREAT (2013). Targeted Retrofit Energy Analysis Tool (TREAT) software. Ithaca, NY: 

Performance Systems Development. http://psdconsulting.com/software/treat/.
35

Appendix A: Description

One method to significantly add insulation to an existing wall in residential construction is to use

exterior wall spray foam insulation with stand-off furring. The advantages of this strategy 

include minimizing the physical connections to each individual existing wall stud, using spray 

foam to encapsulate existing siding materials including lead paint, and creating a vented rain 

screen assembly to promote drying. Field installation indicates that the incremental cost when 

installed as part of a typical siding and window replacement job adds approximately $10/ft2 of 

wall area. 

2 × 4 framing members can be attached to the wall at band joists and top plates using an “L” clip, 

and closed-cell spray foam can be used to insulate the wall after the framing is installed. 

Windows can be installed as the framing is being put up, including extension jambs. 

Figure 35 through Figure 49 illustrate step-by-step instructions for the process of installing 

stand-off furring.
36

Figure 35. Step 1: Assess the existing condition of the wall.
37

Figure 36. Step 2: Remove the existing window trim, and fasten the ledger boards through the 

existing exterior cladding and sheathing.
38

Figure 37. Step 3: Attach the metal “L” clips on the top and bottom ledger board—one on 

either side of where the new vertical 2 × 4 will be attached. Also in Step 3, remove the existing 

window, and install new framing for the new window.
39

Figure 38. Step 4: Install the vertical 2 × 4s, spaced as needed based on structural calculations 

and siding manufacturer requirements.
40

Figure 39. Step 5: Install two horizontal framing members on the top and bottom of the rough 

opening for the new window. Slightly slope the sill framing to the exterior.
41

Figure 40. Step 6: Install the sill pan.
42

Figure 41. Step 7: Install the flexible flashing on the rough opening and 

at least 6 in. up the sides of the jamb.
43

Figure 42. Step 8: Install caulk on the face of the rough opening at the jambs and head. 

Do not caulk the sill.
44

Figure 43. Step 9: Install the new window.
45

Figure 44. Step 10: Install the jamb flashing (flat on the face of the window flange).
46

Figure 45. Step 11: Install the head flashing from the face of the existing wall to lap over the 

head of the new window. Also, tape the flashing at the head using straight flashing tape 

lapped over the horizontal part of the head framing.
47

Figure 46. Step 12: Install the vertical framing members above and below the new window, and 

install the insect screen to the bottom of the new wall. Air seal the window from the interior 

using non-expanding foam sealant, and install internal jamb extensions to prevent exterior 

spray foam from getting into the house. 
48

Figure 47. Step 13: Begin the spray foaming by first spraying the foam around the edges of the 

vertical 2 × 4s to “picture frame” the area. This will also allow the spray foam to extend under 

the 2 × 4 being held off the existing wall by the clips. Secure the framing in place to minimize 

movement of the studs.
49

Figure 48. Step 14: Spray insulation within cavities of the new wall.
50

Figure 49. Step 15: Install the new cladding, and install the new window trim.
51

Appendix B: Computer-Aided Design Details

The computer-aided design details shown in Figure 50 through Figure 56 apply to exterior wall 

framing with spray foam.

Figure 50. Wall at foundation
52

Figure 51. Roof to wall

Figure 52. Wall at floor
53

Figure 53. Window details

Figure 54. Wall to roof
54

Figure 55. Flush rake

Figure 56. Shed roof 
55

Figure 57 and Figure 58 explain the construction of this wall system.

Figure 57. Tear-away view of wall construction

Figure 58. Tear-away view of wall construction from the other side
56

Appendix C: Additional Mockups

The construction of full-scale mockups of key features typical to many existing homes was the 

primary mechanism to allow for tests of the constructability of the proposed strategies. These 

mockups helped in the determination of the amount of materials and labor needed to execute a 

given strategy. They also provided a venue for those responsible for executing these 

unconventional practices in the field to refine application methods and sequencing prior to 

arriving on the job site. Figure 59 through Figure 62 show the design intent (left) and built (right) 

versions of each mockup to start the DER application. These were areas of a general house that 

the team thought might be problematic. 

Figure 59. Detail around exterior door and light fixture
57

Figure 60. Detail around band joist

Figure 61. Detail at second-floor roof
58

Figure 62. Detail at inverted corner and light fixture
59 

Appendix D: Compliance

The following discusses some of the permitting questions that might be asked by authorities prior 

to granting a permit for a stand-off furring type of installation. It may be necessary to obtain the 

seal of a structural engineer in order to be granted the permit. Consult with the local authorities

for permitting requirements. 

For a stand-off furring retrofit project, an analysis of the wall section and other relevant members 

could be done using ASD equations from 2012 NDS (American Wood Council (2012a)) and 

Manual for Engineered Wood Construction (American Wood Council (2012b)). The following 

modes of failure could be considered: 

• Failure of new 2 × 4 studs in compression 

• Failure of mechanical connection of ledger board to rim joist

• Failure of ledger board in shear

• Failure of ledger board in flexure

• Failure of mechanical connection of ledger board to the clip (model number FCB 

43.5) 

• Failure of mechanical connection of the clip (model number FCB 43.5) to stud. 

Regarding loads for each of the wall section parameters, consider the following: 

• Vinyl, fiber cement, and stucco siding 

• Windows approximately the same weight as stucco

• Studs spaced at 16 in. and 24 in. on center. 

The following are the types of questions that might be asked in order to obtain a permit for a 

stand-off furring retrofit project. 

Question: Is 4 in. an adequate screw length? How do we fasten the ledger board?

Response: Four inches is an adequate screw length. All spacing calculations for ledger board are 

based on a screw length of 4 in. 

Based on calculations, walls with stucco and ledger board beneath a window need a minimum 

spacing of 2 ft between screws. With fiber cement siding or vinyl siding, screws can be spaced 5

to 6 ft apart, with the exception of underneath windows. 

Question: Are the clips adequate to hold windows/walls?

Response: The clips must be made to be used in conjunction with steel and, when done so, can 

produce wall connections that withstand thousands of pounds. For example, Simpson Strong-Tie 

technical data suggest a minimum allowable load of 550 lb when fastened to wood with four 
60

SD10112 screws. Based on yield limit theory and the International Code Council Evaluation 

Services measured value of yield bending strength for SD10 screws, a structural lumber to FCB 

43.5 connection was estimated to hold up to 680 lb. The largest dead load was estimated to be 

172 lb. The clip connected with only two screws can hold 248.4 lb.

Question: How should the studs be spaced?

Response: The studs are much more than adequate in compression when spaced 24 in. apart. 

Stud spacing is primarily a function of the fastening/spacing requirements of the siding 

manufacturer.
buildingamerica.gov

DOE/GO-102014-4399 ▪ March 2014

Printed with a renewable-source ink on paper containing at 

least 50% wastepaper, including 10% post-consumer waste.

Printed with a renewable-source ink on paper containing at 

least 50% wastepaper, including 10% post-consumer waste.