Expert Meeting Report: 

Interior Insulation Retrofit 

of Mass Masonry Wall 

Assemblies

K. Ueno and R. Van Straaten 

Building Science Corporation (BSC)

February 2012
ii

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Expert Meeting Report: 

Interior Insulation Retrofit of Mass Masonry Wall Assemblies 

Prepared for: 

Building America

Building Technologies Program

Office of Energy Efficiency and Renewable Energy 

U.S. Department of Energy 

Prepared by: 

K. Ueno and R. Van Straaten

Building Science Corporation

30 Forest Street

Somerville, MA 02143

Technical Monitor: Cheryn Engebrecht

Subcontract Number: KNDJ-0-40337-00

January 2012
iv

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v

Contents

Figures ........................................................................................................................................................ vi

Tables.......................................................................................................................................................... vi

Definitions.................................................................................................................................................. vii

Executive Summary................................................................................................................................. viii

1 Background........................................................................................................................................... 1

2 Meeting Information ............................................................................................................................. 1

3 Meeting Objectives and Agenda ......................................................................................................... 3

3.1 Research Questions.......................................................................................................................... 3

3.2 Agenda ............................................................................................................................................ 4

3.3 Presenter Biographies...................................................................................................................... 4

4 Presentation Summaries ..................................................................................................................... 5

4.1 John Straube: Mass Masonry Insulation Retrofits - Fundamentals and Challenges....................... 5

4.2 Henri Fennell: Variations on a (Mass Masonry?) Theme – With a Touch Of Foam...................... 8

4.3 Mark Bomberg: Issues in the Interior Thermal Upgrade of Existing and Historic Masonry 

Walls .......................................................................................................................................... 10

4.4 Christopher Schumacher: Assessing The Freeze-Thaw Resistance of Clay Brick for Interior 

Insulation Retrofit Projects............................................................................................................ 12

4.5 Kohta Ueno: Masonry Wall Interior Insulation Retrofit Embedded Beam Simulations .............. 14

4.6 Ad Hoc Presentation: Terry Brennan - Disabled Housing Renovation, Utica NY, Circa 2008 .... 15

4.7 Ad Hoc Presentation: Bill Rose - Building Science vs. the Historical Preservation Community . 17

4.8 Ad Hoc Presentation: Len Anastasi - A Solution to Interior Insulation Of Masonry Buildings.... 18

4.9 Meeting Follow Up: Green Building Advisor Blog Post............................................................... 19

5 Discussion........................................................................................................................................... 19

5.1 Question and Answer Discussions................................................................................................. 19

5.2 Group Discussion to Cover Key Questions and Action Items....................................................... 22

5.2.1 Details for Bulk Water Control......................................................................................... 22

5.2.2 Thermal Issues.................................................................................................................. 23

5.2.3 Interior Insulation Material Selection ............................................................................... 23

5.2.4 Insulation Assembly Geometry Effects............................................................................ 24

5.2.5 Energy Savings................................................................................................................. 24

5.2.6 Durability Issues............................................................................................................... 25

5.2.7 Historic Issues................................................................................................................... 25

5.2.8 Capillary Flow and Efflorescence..................................................................................... 25

5.2.9 Non-Specialist Analysis.................................................................................................... 27

5.2.10 Tapered Window Openings.............................................................................................. 27

5.2.11 Experiment and Monitoring Opportunity ......................................................................... 27

References................................................................................................................................................. 28

Appendix A (Agenda, Objectives, Key Questions, Presenter Bios) .................................................... 29
vi

Figures

Figure 1. Photo taken during expert meeting........................................................................................... 1

Figure 2. Pre- and post-retrofit temperature gradients through wall .................................................... 6

Figure 3. Interior retrofit with air gap membrane and drainage detail................................................... 7

Figure 4. AVID installation and diagram (© 2011 by HC Fennell Consulting; reprinted with 

permission) ........................................................................................................................................... 8

Figure 5. “Inside-out” approach (© 2011 by HC Fennell Consulting; reprinted with permission) ..... 9

Figure 6. DELPIN output, non-capillary active insulation, 1999-2004 simulation (Häupl 2010)........ 11

Figure 7. Mock-up of IFT insulation system: two continuous layers of insulation and air gap........ 12

Figure 8. Removal of brick sample, and dilatometry (dimensional change) measurements............ 13

Figure 9. Determination of Scrit value plotting degree of saturation against strain (dilation) ........... 14

Figure 10. Embedded beam uninsulated case (left) and insulated case (right) ................................. 15

Figure 11. Moisture issues at windows in retrofitted building (Brennan 2011).................................. 16

Figure 12. Moisture issues at chapel windows (Brennan 2011)........................................................... 16

Figure 13. Hygric buffer mat and interior insulation application (Anastasi 2011).............................. 18

Figure 14. Hygric buffer mat product, with non-metallic friction fastener.......................................... 18

Figure 15. Drip edges to control surface tension at parapets and sills (Straube and 

Burnett 2005)....................................................................................................................................... 20

Figure 16. Steel angle bolted to masonry to transfer load out of beam pocket ................................. 22

Figure 17. Precast window sill drip edge detail (L); rowlock window sill (R) ..................................... 23

Figure 18. Two-dimensional heat flow modeling party wall (assembly, temperatures, heat flux) ... 24

Figure 19. Hygrothermal simulations of heat flux with uninsulated, 1.5”, and 3” ccSPF walls........ 25

Figure 20. Installation of injectable liquid damp-proofing course (Aida DPC, Remmers Ltd., 

2005)..................................................................................................................................................... 26

Figure 21. Tapered window opening jamb detail and interior view (sill left uninsulated)................. 27

Unless otherwise noted, all figures were created by Building Science Corporation

Tables

Table 1. Expert Meeting Participants ........................................................................................................ 2

Unless otherwise noted, all tables were created by Building Science Corporation
vii

Definitions

ACH Air changes per hour 

ASTM American Society for Testing and Materials

BA Building America Program. More information about BA can 

be found at www.buildingamerica.gov

BSC Building Science Corporation. More information about BSC 

can be found at www.buildingscience.com 

ccSPF Closed-cell Spray Polyurethane Foam

DER Deep Energy Retrofit

DOE U.S. Department of Energy

FT Freeze-thaw

IAQ Indoor air quality

NREL National Renewable Energy Labs. More information about 

NREL can be found at http://www.nrel.gov/ 

ocSPF Open-cell Spray Polyurethane Foam

PCF Pounds per cubic foot

RH Relative humidity

SPF Spray Polyurethane Foam

WUFI Wärme- Und Feuchtetransport Instationär 

(http://www.wufi.de/)

XPS Extruded polystyrene
viii

Executive Summary

The Building Science Corporation team held an Expert Meeting on Interior Insulation Retrofit of 

Mass Masonry Wall Assemblies on July 30, 2011, at the Westford Regency Hotel in Westford, 

MA. Featured speakers included John Straube, Christopher Schumacher and Kohta Ueno of 

Building Science Corporation, Henri Fennell of Building Envelope Solutions, Inc., and Mark 

Bomberg of Syracuse University. Some ad hoc presentations were given by practitioners in the 

audience as well. This was followed by a question-and-answer period and discussion.

Key results from this meeting were:

• Greater understanding of the state-of-art in assessing risks or and performing interior 

insulation retrofit of mass masonry wall assemblies

• Greater understanding of the uncertainties in assessments

• Definition of key research needs to investigate and potentially reduce uncertainties.

Extensive information was presented on assessment of risk factors for premature building 

deterioration due to interior insulation retrofits, and methods to reduce such risks. 

It was found that conflicting understanding exists, such as general assessment approaches, 

assessments of masonry material properties, and the inclusion of air spaces between insulation 

and masonry units in hygrothermal analysis. Little research has been conducted on these issues,

as well other major key issues such as the impact the architectural detailing has on rainwater 

concentration, timber beam pocket strategies, and below grade strategies.

The next steps are to define projects to address the research needs identified at the meeting. One 

upcoming retrofit was put forward as an opportunity to experiment with methodologies.
1

1 Background

There is a large stock of uninsulated mass masonry buildings across the United States. The 

retrofit of interior insulation is commonly implemented to improve energy performance of these 

buildings, while maintaining their often historic exterior appearance. There are known durability 

issues associated with interior insulation, such as interstitial condensation and freeze-thaw 

damage issues. In many cases, these issues have been or are being addressed, but there are still 

remaining questions that should be answered before mass implementation in a variety of climate 

zones.

However, leaving these buildings uninsulated is at odds with the Building America target of 

broad energy retrofits of existing homes to reduce residential carbon emissions 20% by 2020 and 

80% by 2050.

2 Meeting Information

Building Science Corporation held an Expert Meeting on Interior Insulation Retrofit of Mass 

Masonry Wall Assemblies on July 30, 2011, at the Westford Regency Hotel in Westford, MA. 

There were 38 in attendance; two participants attended by webinar. Invited speakers gave 

presentations in their particular area of expertise. Three additional experts also gave brief 

presentations of their significant case studies and/or history with these issues. The presentations 

were followed by discussion with the expert audience.

Figure 1. Photo taken during expert meeting
2

The final agenda for the meeting is listed in Appendix A. The presentations are included in 

Appendix B through H. A list of attendees is included in Table 1.

Table 1. Expert Meeting Participants

Name Organization Email Address

Linda Wigington Affordable Comfort lwigington@affordablecomfort.org

Aaron Davenport BASF aaron.davenport@basf.com

Charlise Goodbread BASF charlise.goodbread@basf.com

Chris Little BASF chris.little@basf.com

Henri Fennell HC Fennell Consulting hFennell09@gmail.com

Betsy Pettit Building Science Corporation betsy@buildingscience.com

Chris Schumacher Building Science Corporation chris@buildingscience.com

Joe Lstiburek Building Science Corporation joe@buildingscience.com

John Straube Building Science Corporation john@buildingscience.com

Ken Neuhauser Building Science Corporation ken@buildingscience.com

Kohta Ueno Building Science Corporation kohta@buildingscience.com

Peter Baker Building Science Corporation pbaker@buildingscience.com

Randy Van Straaten Building Science Corporation randy@buildingscience.com

Paul Eldrenkamp Byggmeister Design Build paul@byggmeister.com

Terry Brennan Camroden Associates Inc. terry@camroden.com

Steve Marchese CEDA smarchese@cedaorg.net

Mac Shelden Demilec mac@sheldon.com

Gary Parsons Dow gdparsons@dow.com

Dave Kimball Dow Corning dave.kimball@dowcorning.com

Len Anastasi Exo-Tec Consulting len@exo-tec.biz

Jan Kosny Fraunhofer-MIT Center for Sustainable 

Energy Systems jkosny@fraunhofer.org

Martin Holladay Green Building Advisor mholladay@taunton.com

Emerson Dahmen Habitat for Humanity Merrimack emerson@merrimackvalleyhabitat.org

James Comeau Habitat for Humanity Merrimack mjtupware@comcast.net

David DeRose Halsall dderose@halsall.com

Duncan Prahl IBACOS dprahl@ibacos.com

Hartwig Künzel Fraunhofer Institute for Building Physics hartwig.Künzel@ibp.fraunhofer.de

Ed Reeves Icynene ereeves@icynene.com

Edward Haber Illinois Home Weatherization Assistance 

Program edwardhaber@hotmail.com

John Inglese Inglese Architecture & Engineering j.inglese@inglese-ae.com

Marie McMahon National Grid marie.mcmahon@us.ngrid.com

Marcus Bianchi NREL marcus.bianchi@nrel.gov

Manfred Kehrer ORNL kehrerm@ornl.gov

Achilles Karagiozis Owens Corning achilles.karagiozis@owenscorning.com
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Name Organization Email Address

Bill Rose University of Illinois wrose@illinois.edu

Pat Huelman University of Minnesota phuelman@umn.edu

Mark Bomberg University of Syracuse mbomberg@rogers.com

Emily Vance University of Waterloo ervance@uwaterloo.ca

Rob LePage University of Waterloo rtmlepage@gmail.com

3 Meeting Objectives and Agenda

The objective of this session was to explore the current state of implementation and research on 

interior insulation retrofit of mass masonry wall assemblies. Discussions on this topic were 

applicable to existing mass masonry single- and multi-family residential buildings. The meeting 

consisted of presentations and discussion related to interior insulation retrofit evaluation and 

implementation strategies. Issues such as durability, energy performance, and detailing were

discussed. Differing approaches and areas of need for research to resolve uncertainties in such 

approaches were sought.

.

3.1 Research Questions

Building Science Corporation posed the following research questions relevant to this area of 

study:

• What are typical details required to reduce rainwater exposure, thus balancing out 

reduced inward drying with reduced wetting from the exterior? Are typical existing 

surface drainage details (e.g., solid stone sills, window “eyebrows,” band courses) 

sufficient, or is it necessary to retrofit additional protection?

• What are the energy savings associated with interior insulation retrofits? Can effective 

thermal performance be obtained by leaving these buildings uninsulated, and relying on 

thermal mass effects?

• What is the current level of understanding of evaluating the in-service post-retrofit 

freeze-thaw resistance of a masonry enclosure, using material property testing and 

hygrothermal simulations? Can this process be developed further, and/or streamlined?

• What are effective solutions to address durability concerns at moisture-sensitive 

structural members (e.g., wood beams and joists) embedded in masonry structures, in a 

post-retrofit situation?

• What are some key issues that need to be addressed when interfacing with historical 

preservation requirements (e.g., National Park Service tax credits) and performing these 

retrofits?

• Are there retrofit methods to reduce capillary uptake through existing masonry structures, 

which are simpler (and less costly) than the retrofit of regletted capillary breaks?

• Based on hygrothermal simulations and field experience, are there widely-applicable 

limits to interior insulation levels (and type of insulation), based on climate zone, 

building exposure, and material properties that can be evaluated by non-specialists?
4

• Are there cases of building enclosure failures that can be traced directly to the retrofit of 

interior insulation, and what were the circumstances and contributing factors in the 

failures?

• Given that many mass masonry buildings have deep window openings with limited 

available space (due to window clearance issues), what is the effect of thinner (e.g., ~1”) 

insulation at these openings?

3.2 Agenda

• 9:00 AM Welcome and Meeting Introduction

o Brief Building America Program Overview

• 9:15-10:00 AM John Straube: Mass Masonry Insulation Retrofits: Fundamentals and 

Challenges

• 10:00-10:30 AM Henri Fennell: Variations on a (Mass Masonry?) Theme – With A 

Touch Of Foam

• 10:30-10:45 AM Break

• 10:45-11:15 AM Mark Bomberg: Thermal Upgrade of Masonry Walls - Interior Methods

• 11:15-11:45 AM Christopher Schumacher: Assessing the Freeze-Thaw Resistance of 

Clay Brick for Interior Insulation Retrofit Projects

• 11:45-12:15 AM Kohta Ueno: Masonry Wall Interior Insulation Retrofit Embedded 

Beam Simulations

• 12:15 to 1:15 Lunch break (lunches provided)

• 1:15 to 1:45 Special Topic Discussions

o Field experience of field practitioners not on speakers list

o If warranted—collect photos for display and discussion over lunch break from 

field practitioners

o Discussion of problematic water concentration details seen in the field

o Discussion of retrofit details to reduce water exposure

• 1:45 to 3:00 Group discussion to cover key questions, action items, follow-up plan, and 

wrap-up.

• 3:00 PM Adjourn meeting

3.3 Presenter Biographies

John F. Straube (Ph.D., P.Eng.) is a principal of Building Science Corporation and a professor of 

building science in the Civil Engineering Department and School of Architecture at the 

University of Waterloo, Canada. Dr. Straube has acted as an educator, researcher, consultant and 

expert witness on energy efficiency, durability and IAQ. Current interests include the optimal 

system design of buildings, sustainable buildings, and moisture problem avoidance. 
5

Henri Fennell (CSI/CDT) is a principal of HC Fennell Consulting, a building science consulting 

and education firm. He is an architect with twenty-five years of experience in energy 

conservation products and services, and specializes in the use of manufactured and field-installed 

urethane technologies. As a building envelope consultant, Henri worked with architects, 

designers, builders, and contractors to diagnose and solve building envelope problems. Before 

this position, he was president of Building Envelope Solutions, Inc. / FOAM–TECH, a spray 

foam contracting firm, and then Technical Research Manager at Conservation Services Group, 

Inc.

Mark Bomberg (Ph.D.) is a research professor at Syracuse University. He is a leader of an 

industry-university collaborative research center on hygrothermal performance of building 

enclosures. His research specialties include high performance building enclosures and thermal 

insulating materials. Prior to this position, he was a senior researcher at the National Research 

Council of Canada for 24 years.

Christopher J. Schumacher (M.A.Sc.) is a principal of Building Science Corporation. He is 

recognized as an expert in the field of building monitoring and building systems and enclosure 

testing. He has led the design, installation and analysis of monitoring systems for 15 building 

enclosure test facilities, 6 test building sites, 3 climate chambers and 2 sustainable building 

technologies demonstration projects in over a dozen states and countries as far abroad as 

Mongolia and New Zealand.

Kohta Ueno (M.A.Sc.) is a senior associate of Building Science Corporation. His responsibilities 

at Building Science Corporation include project management, liaison work with builders and 

industry clients, HVAC design, energy analysis of house designs, computer modeling, field 

testing and verification, and forensic field investigations. He has been with BSC since 1998, and 

completed his Master’s degree with the Building Engineering Group under John Straube at the 

University of Waterloo in 2007.

4 Presentation Summaries

Five main presentations were given describing current approaches to interior insulation retrofit of 

masonry buildings. In addition, three “ad hoc” presentations were given by practitioners, 

regarding specific evaluation and insulation approaches as well as the relationship between the 

building science community and the historical preservation community.

4.1 John Straube: Mass Masonry Insulation Retrofits -

Fundamentals and Challenges

In his presentation, Dr. Straube first noted that there are many different types of assemblies—

solid brick or stone masonry, terra cotta backup or CMU backup wall, etc. In addition, the face 

brick and core brick have different properties: face brick tends to be the highest quality brick 

(well-fired) and core brick the worst (under- and over-fired).

Generally, the outside of building sees the same rain and similar temperatures pre- and postretrofit. However, the biggest changes are inside the wall, where the assembly previously saw 
6

moderated temperatures and is now experiencing colder conditions (Figure 2). Hence, the 

question is whether there is a potential for freeze-thaw damage deeper in the wall.

Figure 2. Pre- and post-retrofit temperature gradients through wall

Other impacts of interior insulation retrofits are that the assembly had reduced drying to the 

interior, and the amount of energy flow through the wall (and thus drying potential) has been 

minimized. 

There is a condensation risk at the masonry-to-insulation interface. In early days of retrofits 

(1970s oil crisis), steel stud and fiberglass batt were installed and covered with polyethylene on 

the interior. However, air leakage could bypass imperfectly installed polyethylene vapor 

barriers/air barriers, resulting in condensation problems. This condensation-based wetting would 

occur in a spot that is at freezing temperatures, post-retrofit. Although this interface was hidden, 

it became a durability issue, manifested as the assembly degrading and spalling.

Another concern is rot/corrosion of embedded elements. An interesting aspect of this issue with 

interior insulation retrofits is that although the assembly may have higher moisture contents, it is 

also much colder—which slows the rate of corrosion and rot.

Embedded wood timbers are a common embedded element of durability concerns. A number of 

solutions are being pursued, including borate injections into the wood, metal wedges next to the 

member (to provide passive heat flow), active heating, or construction of a load bearing structure 

inside of the masonry, and cutting off the end of the beam.

When considering windows within such structures, rain and thermal continuity (avoiding thermal 

flanking) are paramount for good performance. There needs to be a minimum insulation value to 

prevent frosting and condensation. Rain penetration at the window-to-wall interface and the 

effect of rain concentration features need to be addressed through good detailing.
7

Currently, 2.0, 1.0, and 0.5 pound per cubic foot (pcf) polyurethane foams are commonly used 

for interior insulation. There is little guidance available to design teams on selection of these 

products, which may become more significant issues as additional products are brought onto the 

market.

Another interesting option is to use board foam products. One recommended detail is the 

application of a liquid-applied vapor permeable air and water barrier on the interior face of the 

masonry, and semi-permeable foam.

The team had opportunity to inspect a building in Regina, SK, which had 4” polyisocyanurate 

board foam applied to interior in 1982. There was no damage to the masonry; however, one 

needs to recognize that Regina is in a very dry climate zone (~14”/year precipitation).

Mass or storage walls, by their nature, do not require a separate drainage system, instead relying 

on safe storage of moisture in the mass of the system. However, there are cases where leakage 

occurs in the existing building, or thin (2-wythe) masonry provides inadequate storage. This 

might be addressed with an interior drainage system (Figure 3). This need can be evaluated 

onsite by looking for staining, rot, and from historical knowledge of facility maintenance staff. 

However, the interior drainage detail is difficult to implement, is high risk, and should be 

considered the last response. One troubling detail is drainage of the flashing connection at the 

floor slab interruptions. The drilling of the sloped drained hole to the outside is a high risk and 

particular detail.

Figure 3. Interior retrofit with air gap membrane and drainage detail

A series of six recommended evaluation steps were presented: each incremental step reduces 

uncertainties in the evaluation. They were, in order of importance:

• Site Visit Assessment (assessment of rain leakage, poor detailing, existing freeze-thaw 

damage)
8

• Simple Tests and Modeling (dry density, liquid water uptake, saturation moisture content, 

and basic hygrothermal/WUFI modeling)

• Detailed Tests and Modeling (thermal conductivity, Fagerlund’s Critical Degree of 

Saturation or Scrit)

• Site Load Assessment (assessment of driving rain load, run down patterns; monitoring of 

rain deposition with driving rain gauges is the most thorough method)

• Prototype Monitoring (retrofit of a small area of the building, and monitoring of 

temperature and moisture content, including comparisons to models)

• Maintenance and Repair (creating a recommended program of inspection/repair, perhaps 

in the form of a building owner’s manual)

Dr. Straube concluded by stating that the concept of freeze-thaw failure being a pass/fail digital 

test is a fundamentally wrong assumption, as discussed in more detail by Schumacher. View Dr. 

Straube’s presentation.

4.2 Henri Fennell: Variations on a (Mass Masonry?) Theme –

With a Touch Of Foam

Mr. Fennell opened his presentation by describing the Air, Vapor, Insulation, Drainage (AVID) 

approach, which is an interior insulation/drainage detail applied to basements and crawl spaces 

(Figure 4). Interior spray foam was deemed inadequate for management of bulk water alone, 

without intentional drainage. The recommended AVID approach is shown in Figure 4: it 

involves draping polyethylene from grade to a perimeter drain, and then applying spray foam. 

Some specific details of this approach are to treat wood beams buried in the insulation with 

preservatives, and to include a “drip edge” detail at the bottom of the plastic sheet to drain the 

water into the gutter (to avoid water intrusion at the basement slab).

Figure 4. AVID installation and diagram (© 2011 by HC Fennell Consulting; reprinted with 

permission)
9

AVID examples included the Gilman Housing project (using Tu-Tuff reinforced polyethylene), 

and the Westford House/Barn (see Pettit 2008 and Lstiburek 2010a), which used self-adhered 

membrane. Collected data indicated that these basement insulation retrofits result in the 

basement/crawl space operating close to interior conditions (including dewpoint/air moisture 

levels).

Next, Mr. Fennell presented the “Inside-out Approach” (Figure 5), which involves using the 

existing masonry wall as a rainscreen. It was typically applied to failed brick veneer/steel stud 

backup walls, where the backup wall suffered bulk water intrusion, resulting in mold and mildew 

damage. One approach was to install a polyethylene drainage plane inside of the brick veneer, 

draining to a water management gutter at the floor level. This approach could be applied to mass 

masonry walls as well.

Figure 5. “Inside-out” approach (© 2011 by HC Fennell Consulting; reprinted with permission)

One installation detail makes use of the fact that when spray foam is applied on flat 

polyethylene, differential cooling will draw the polyethylene inward, creating a 1⁄2” to 1-1⁄4” air 

space in middle of framed elements. Alternatively, a drainage mesh (e.g., Obdyke Cedar 

Breather) could be used to intentionally create the air space behind the polyethylene. A potential 

advantage of the approach is its reversibility for historic projects. An alternate approach is to 

create an entire stand-alone structure (such as SIPS panels) inboard of the existing structure. 

Small scale reversibility at discrete locations (e.g., blocked-off basement windows) can also be 

achieved through use of rigid foam insulation plugs with polyethylene (as a bond break).

This was followed by review of several case studies, showing highlighted design approaches to 

interior masonry insulation applications and described below.

Berkshire Elderly Housing (Pittsfield, MA 2004): This project highlighted the use of closed wall 

cavity (plaster wall with strapping) retrofit insulation, using closed cell SPF. Many application 

holes (~12” o.c.) were required in order to achieve full coverage. Excess foam was trimmed flush 

© 2011 by HC Fennell Consulting
10

at the application holes; a layer of gypsum board was applied as a finish surface (as opposed to 

patching the plaster) for cost reasons.

Brady, Patrick Residence (Gloucester, MA 1995) was a project with stone walls and vaulted 

arches, which required insulation above these stone arches. The team was limited to a single 

application hole at each vault apex; however, infrared scans showed that good coverage was 

achieved.

Buster, Cami Residence (Fairlee, VT 1990) provided an interesting anecdote: it was a stone 

building with interior spray foam which subsequently suffered from a fire. To everyone’s 

surprise, the ccSPF walls were not damaged; the foam apparently acted as fire blocking, 

eliminating paths for superheated air to travel through the assembly.

Keene State College Fiske Hall (Keene, NH 2008) was a dormitory renovation done using open 

cell spray foam (ocSPF). One challenge was that the stud bay cavities were completely filled, 

and due to expansion of the ocSPF, the trimmed excess was comparable to the amount of foam 

applied to the wall. This brings into question the cost savings of open cell, when excessive 

trimming is required.

A number of additional projects were presented. Mr. Fennell’s firm initially did more closedcavity injection projects, rather than open cavity (surface sprayed) projects. One of the reasons 

for the popularity of injection was that this is typical for the manufacturing field, which was his 

background. Almost all of his early 1980s jobs were closed cell cavity fill.

Mr. Fennell would typically assess freeze thaw risks by calling in experts (such as BSC or Mark 

Bomberg). In some cases, his firm sent away samples for detailed analysis. There were only a 

few cases where it was discovered that there was an outright problem with interior insulation. He 

has done many projects all over North America and has never had a call-back regarding ensuing 

damage. View Mr. Fennell’s presentation.

4.3 Mark Bomberg: Issues in the Interior Thermal Upgrade of 

Existing and Historic Masonry Walls

In his presentation, Dr. Bomberg first provided some basic background on interior insulation 

retrofits. He then asserted that any masonry building can be insulated on the interior if a 

“capillary active layer” (CAL) or “capillary active material” is used. Such insulation material is 

vapor diffusion-open and capillary active: as a result, interior moisture condenses on cold side, 

but the moisture is transported back to interior by capillarity. As this material is vapor-open, it 

does not inhibit drying to the interior. The industry has had—as Bomberg puts it—a “ridiculous 

fear of water” in construction. However, it is the effect of water—not the presence of water—

that is critical. Designs are generally acceptable if they avoid mold growth and allow drying.

A case study was presented based on analysis done in Germany using the DELPHIN 

hygrothermal simulation (Figure 6); the graph gives results over five simulated years, showing 

moisture content through the thickness of the assembly. Low moisture contents were noted 

through the thickness, but with higher levels at the interior and exterior layers. Wintertime 

condensation was observed at the insulation-to-masonry interface when a non-capillary active 

insulation was used (left-hand spikes in Figure 6). In contrast, capillary active insulation reduced 
11

interior moisture contents; however, it resulted in increased exterior moisture content levels 

relative to the previous (non-CAL) case.

Figure 6. DELPIN output, non-capillary active insulation, 1999-2004 simulation (Häupl 2010)

These simulations indicated that the capillary active layer needs to use nano-technology, which 

will create pores sized at a level that directly affects water capillary (“micropores”). Material 

development of several calcium silicates formulations to meet these requirements was described. 

The actual insulation product is a solid sheet material; there are five commercial manufacturers 

of this material in the US, for industrial applications.

Dr. Bomberg presented a case study where such products were used in the Church of Our Lady 

in Dresden, Germany. A second application is presented for Rijksmuseum Amsterdam, where 

the architect initially proposed foam glass. Simulations showed high moisture content at the 

interface; these levels were lower when a capillary active layer (calcium silicate) was used

(allowing inward drying).

One key to the use of the capillary active layer is to ensure capillary contact between the 

masonry and the insulation; various plasters were used for this purpose. A project in Sapporo,

Japan, used an assembly combining clay plaster on the interior, followed by a layer of lime 

plaster. Monitored results are being collected and compared with simulations. German climatic 

plaster (high clay content, capillary active) is also used in this application, between calcium 

silicate and masonry.

A completely different system was subsequently presented, which was the Integrated Façade 

Technology (IFT) wood fiber insulation system, manufactured in France, Germany, and Japan. 
12

Dr. Bomberg prefers this product over calcium silicate. The system consists of spray foam 

against masonry, a ventilated air gap, a treated wood fiberboard insulation board, and a lime 

plaster finish (see Figure 7). The recommended spray foam products are between 1.1 pcf and 3.5 

pcf. In this application, the limit is 1.5” of closed cell, to allow for drying. Future work includes 

research on this moisture active thermal insulation layer, including the potential to integrate it 

with heating, cooling and ventilation, air conditioning systems. View Dr. Bomberg’ presentation.

Figure 7. Mock-up of IFT insulation system: two continuous layers of insulation and air gap

4.4 Christopher Schumacher: Assessing The Freeze-Thaw Resistance of Clay 

Brick for Interior Insulation Retrofit Projects

Mr. Schumacher presented the current state of assessing the freeze-thaw resistance of clay brick; 

he introduced the topic by covering the basics of moisture storage and transport in porous 

materials (as per Straube and Burnett 2005). Then, he presented four historic and current theories 

of the mechanisms that cause freeze-thaw degradation at a microscopic level:

Closed Container Theory: Water expands 9% upon freezing (demonstrated to be a questionable 

mechanism by 1930s experimental work).

Ice Lensing Theory: Water migrates from warm water to sub-zero ice, displacing material as it 

travels.

Hydraulic Pressure Theory: As ice forms, liquid water is displaced and either “high pressure 

flow” or “dead end traps” occur.

Disequilibrium Theory: Moisture in unfrozen pores connected by capillaries to frozen pores

(similar scenario to ice lensing) move by diffusion, causing damage.

He asserts that in reality, a combination of these mechanisms is likely at play, explaining 

anomalies seen in masonry performance.
13

The literature indicates that current ASTM tests used in industry (ASTM C62 and C67, and the 

cold soak/boil or c/b ratio) are not reliable determinants of freeze-thaw risks, resulting in both 

false positives and false negatives.

The frost dilatometry testing techniques (building on Fagerlund’s work) developed at BSC were 

then presented; this work is covered in more detail by Mensinga et al. (2010), and Lstiburek 

(2010b). The fundamental problem with the existing freeze-thaw resistance measurements is that 

they are digital tests (pass/fail). In reality, there is a continuum of performance, based on the 

exposure of the brick. This technique measures the critical degree of saturation (or Scrit) of a 

masonry material. At water contents below Scrit, no freeze-thaw damage will occur regardless of 

number of freeze-thaw cycles, while above Scrit, damage is measurable after only a few cycles.

The measurement involves removal and preparation of brick samples from the building, freezethaw cycling them at various moisture contents, and measuring dimensional changes of the 

sample (see Figure 8).

Figure 8. Removal of brick sample, and dilatometry (dimensional change) measurements

Scrit level can be determined by plotting sample dimensions before and after thermal cycling, at 

various moisture contents (Figure 9). If the sample grows, then freeze thaw degradation is 

occurring and that sample’s moisture content is above the Scrit threshold. This threshold can 

subsequently be used as a limit state in evaluating hygrothermal model outputs.

Work for the future includes refinement and documentation of the dilatometry test method, 

documentation practices for assessing buildings (material conditions and moisture distribution 

and loads), and development and documentation methods to address moisture concentrations.

View Mr. Schumacher’s presentation.
14

Figure 9. Determination of Scrit value plotting degree of saturation against strain (dilation)

4.5 Kohta Ueno: Masonry Wall Interior Insulation Retrofit 

Embedded Beam Simulations

Mr. Ueno first presented a literature review of research on moisture issues in wood beams 

embedded in masonry, which become colder (and have less available drying) after interior 

insulation retrofits. One researcher measured embedded joist moisture contents after interior 

insulation: one case remained substantially dry, while another showed elevated moisture contents 

after insulation. It was theorized that the latter case involved bulk water control or capillarity 

issues (i.e., exterior moisture loadings). Other researchers performed hygrothermal and thermal 

analysis, in order to predict the moisture effect of retrofit insulation and the heat loss effects of 

leaving a wide gap in the insulation surround the embedded member.

The first portion of the current work was a series of three-dimensional heat transfer simulations, 

which demonstrated a number of phenomenon, including 

Insulating the entire wall lowers the temperature of embedded wood.

Installing metal “heat spreader” plates at the sides of the member (bypassing the insulation) 

raises the wood temperature, albeit limited by the dimensions of the embedded member.

Omitting the insulation surrounding the embedded wood effectively raises the temperature.

Applying reduced thicknesses of insulation was not effective at raising the wood temperature.
15

These results applied to both embedded heavy beams and smaller dimension lumber floor joists. 

The heat transfer analysis showed that the addition of metal plates reduced the heat loss savings

(due to insulation) by 9%, and that having an uninsulated band had a 20% “giveback” effect.

Figure 10. Embedded beam uninsulated case (left) and insulated case (right)

These results were then used as inputs to one-dimensional hygrothermal simulations. In a onedimensional limitation, the insulated and uninsulated cases have identical geometries. Therefore, 

a “temperature index” approach was used, taking the three-dimensional results and modifying 

the thermal conductivity of the wood beam to approximate the temperature conditions. In 

addition, the effect of interior air leakage into the beam pocket was analyzed.

Initial simulations showed that the air gap between the beam end and the masonry needed 

generous ventilation to the interior to maintain tolerable moisture content levels in the wood, 

even in the uninsulated case. Insulation had mixed results, such as higher wintertime moisture 

contents, but similar summertime levels. Changing the exterior masonry material had a major 

impact on embedded wood member moisture contents, raising uncertainty of the results of this 

approach. Mr. Ueno made it clear that caution should be used in interpreting these results, as 

there is a high degree of uncertainty regarding the accuracy of this simulation approach, and the 

absence of monitored hygrothermal conditions for which to compare such models. Future work 

could include the use of two-dimensional hygrothermal simulations, and field monitoring of 

embedded wood members. View Mr. Ueno’s presentation.

4.6 Ad Hoc Presentation: Terry Brennan - Disabled Housing Renovation, Utica 

NY, Circa 2008

Mr. Brennan presented a case study in a masonry building retrofitted with interior insulation 

(urethane spray foam and steel framing) that showed signs of failures. 

The building owner initially reported mold issues around the window penetrations on the top 

floor of the building (particularly at arch-top windows), on all orientations. It was found that this 

was not mold, but re-emulsification of gypsum drywall compound due to bulk water penetration 
16

(see Figure 11); the compound was sufficiently wet and plastic that it could be “ribboned” like 

clay.

A diagnosis of the building exterior revealed a series of details that concentrate exterior 

rainwater at vulnerable locations, for instance, the window pan coping deposits rainwater onto 

the existing stonework, where it concentrates at the grout joint (Figure 11). A preferred approach

would be a metal water shedding detail that covers the entire sloping stonework, with a drip edge 

1” off the face of the stonework, to shed the water from the masonry. Other poor masonry 

detailing was observed throughout of the building, resulting in the observation that builders did 

not necessarily make buildings “better in the old days”—instead, only the well-detailed buildings 

have survived until today.

Figure 11. Moisture issues at windows in retrofitted building (Brennan 2011)

Brennan also observed newly occurring freeze-thaw damage in the cast stone material. At the 

chapel section, damage was observed at some of the arch-top windows, with an interior ceiling 

vault, and spray foam at the exterior wall (Figure 12). Excavation at the damage site showed 

plaster degradation and rust of the reinforcement mesh and steel framing.

Figure 12. Moisture issues at chapel windows (Brennan 2011)
17

Investigation revealed that the problem windows were surrounded by wet masonry, while the 

non-problem windows had dry masonry (as confirmed by measurements with a electrical 

capacitance moisture meter). All windows that showed damage had obvious water management 

defects in the brickwork above. Site work showed that it is often difficult to get an honest 

assessment of the building from the occupants and staff.

This case study provides a valuable example of details that were sufficiently problematic to 

cause long-term problems. A site assessment should be used to look around the building, observe 

where water comes in, how it comes in, and how it can be kept out of the wall. The most 

important recommendation is that if rain control cannot be addressed and upgraded, interior 

insulation should not be implemented. View Mr. Brennan’s presentation.

4.7 Ad Hoc Presentation: Bill Rose - Building Science vs. the Historical 

Preservation Community

Mr. Rose discussed conflicts between the historical preservation community and the building 

science community; these are two distinct “camps,” each with their own sphere of influence and 

self-identified practitioners. Due to current developments, the preservation community believes 

that building science is seeking to assert an “undue influence” on their field.

The communication gap that exists between these two communities is exemplified, for instance, 

by the National Park Service/Technical Preservation Services Preservation Brief 03: Conserving 

Energy in Historic Buildings (circa 1978). It simply gave the guideline to “insulate historic 

buildings, but use a vapor barrier,” which is misguided thinking that practice has long since been 

surpassed. Mr. Rose was a reviewer in a recent effort to update the guide. In response to this 

work, he wrote a white paper which included the following generalization: “I can give you a 

historic building with great energy efficiency, durability measured in centuries, and exposure of 

historic elements... choose two out of three.” However, this statement was not well received by 

preservation community.

Mr. Rose discussed a few examples of how deterioration was addressed at projects where he was 

involved. His key messages were that insulation can have an impact, some problems are 

complex, and that convincing historical preservation groups to address water management 

(through even slight architectural modifications) can be very difficult.

The preservation community typically wants to know “how much wetter will my building get?” 

and “how wet is too wet?” He suggests that the building science community needs to provide 

whatever knowledge that it can offer on these questions: however, the answer is often only 

general guidance on risks, with a strong degree of uncertainty. Unfortunately, the 

preservationists want a high degree of certainty, as the result of failed insulation strategies that 

were implemented in the 1970s.

He concluded by suggesting that the focus would be better directed at ongoing building 

maintenance, and that interior insulation should only be allowed conditionally with an increase 

of the ongoing maintenance budget. This is a practical solution that property owner could use to 

seek appropriate budgets to resolve the most likely causes of premature water-related damage 

during the life of the building.
18

Note that no presentation materials were provided during Rose’s talk.

4.8 Ad Hoc Presentation: Len Anastasi - A Solution to Interior Insulation Of 

Masonry Buildings

Mr. Anastasi presented his preferred approach to interior insulation retrofits of masonry 

assemblies. His solution involves attaching a drainage mat covered with a polyolefin film to the 

interior of the masonry, and applying closed cell spraying foam inboard of that material. The 

point of the cavity is that bulk water in incidental locations could be drained and/or redistributed 

without concentrated damage to the immediate area. It allows greater drying to the masonry, 

compared to direct application of ccSPF to the interior surface. This application has been 

developed into a commercial product, marketed as a “hygric buffer mat.”

Figure 13. Hygric buffer mat and interior insulation application (Anastasi 2011)

The mat is attached to the masonry with non-metallic friction fit plastic fasteners, typically with 

a 2’ o.c. spacing.

Figure 14. Hygric buffer mat product, with non-metallic friction fastener
19

Several application examples were given, such as the Water Works Condominiums, in Chestnut 

Hill, MA (2006): there have been no call backs or apparent problem. One option for this air gap 

assembly is that if a problem developed, a fan could be installed to pressurize the “buffer mat” 

cavity with interior air, to dry out any moisture issues. View Mr. Anatasi’s presentation.

4.9 Meeting Follow Up: Green Building Advisor Blog Post

One of the attendees (Martin Holladay, Green Building Advisor) writes a regular column 

(“Musings of an Energy Nerd”) for the Green Building Advisor website, which is a collaboration 

between BuildingGreen.com (the publishers of Environmental Building News) and Taunton 

Press. His column for August 12, 2011 (“Insulating Old Brick Buildings: If you’re thinking of 

insulating the interior of a load-bearing brick wall, proceed with caution”) was a summary of this 

Expert Meeting and the post-meeting discussion. This presents another method to distribute the 

information presented in this Expert Meeting to the building community. Read the blog post; it 

includes the comments/discussion on the post.

5 Discussion

The primary purpose of the discussion portion of the meeting was to identify key questions in 

industry regarding the evaluation and implementation of interior insulation retrofit strategies.

They are presented here in a question-and-answer format.

5.1 Question and Answer Discussions

The following items were follow-up discussions from the various presentations, and topics of 

interest to the speakers and the audience.

Q: Is the parapet condition a good test of the suitability of interior insulation retrofit?

A: This is a reasonable test, but not a 100% answer by any means. The parapet could have been 

built from a different brick, have greater exposure due to poor cap flashing details, or higher 

exposure due to cracking at the base of the parapet from expansion and contraction. Furthermore, 

they are different than typical above-grade walls, due to solar exposure on both sides of the 

assembly.

Q: With the caveats to using software tools such as WUFI to evaluate the risk of premature 

freeze thaw degradation due to interior insulation retrofit, is such an analysis worthwhile?

A: WUFI analysis should be done by experts. If done well, it can provide confidence in 

likelihood of success of the retrofit installation.

Q: Is brick testing necessary for evaluating the risk of premature freeze thaw degradation due to 

interior insulation retrofit?

A: It has importance; however, it should be considered secondary to the site assessment. The 

loading due to bulk water concentrations (as observed during the site assessment) can far 

overwhelm any analysis determining limits for Scrit. The scope of the investigation depends on 

the nature of the project, and the acceptable degree of uncertainty. In the cases of historically 

significant or landmark buildings, a more in-depth investigation to limit uncertainty is 

recommended.
20

Q: Is there data available on impact of drip edge distances, and on the degree of water 

concentrations due to surface conditions in general?

A: There is definitely a dearth of research on this topic. However, there are general, simple

concepts that should be observed and followed. More research in the area is needed, in order to 

develop unobtrusive drip edges that will meet historic requirements.

Figure 15. Drip edges to control surface tension at parapets and sills (Straube and Burnett 2005)

Q: What is the impact of having an air gap between the insulation and the masonry (as per the 

“hygric buffer mat” discussion above)?

A: A great degree of disagreement was evident amongst the participants and the speakers,

regarding the risks and merits of such air gaps. In some cases, air gaps are intentionally added, 

while in others, they are specifically avoided. The risk of adding an air space is that the “buffer” 

space will be damp, resulting in mold growth (and IAQ problems if there is any air connection 

from the “buffer” space to the interior). In addition, there is a potential for air leakage from the 

interior to the “buffer” space, which could introduce additional moisture to the assembly. The

benefit of the “buffer” space is that damp wall areas can potentially dry via air convection to less 

damp areas, thus minimizing localized degradation. In addition, in cases of severe loadings, 

dried, heated, and conditioned air could be injected into the cavity, to dry the assembly.

Q: Should we be using open or closed cell foam in these applications?

A: Open cell spray foam (ocSPF) is sufficiently vapor permeable (“vapor open”) that there is 

some risk of frosting or condensation at the interface between the insulation and the masonry, 

especially at elevated relative humidities. In addition, inward driven water vapor can be a factor 

with open cell foam: impermeable finishes that act as a vapor barrier (e.g., glass picture frames, 

mirrors mounted on exterior walls) should be eliminated, due to summertime condensation risks. 

Closed cell spray foam (ccSPF) does not suffer from either of these issues; however, it 

substantially reduces the drying of the masonry to the interior, compared to ocSPF.

Q: Are clear protective sealants (silanes and siloxanes) a good solution to accompany these 

retrofits?

A: There was significant disagree amongst the participants. Some practitioners have used these 

products on a number of projects without issues (DeRose, Halsall). Others bring up the two 
21

decades of experience (some of it extremely negative) with sealers in the preservation industry, 

which has led them away from sealants. The worst issues occur when bulk water enters the 

masonry in macroscopic cracks (which the sealants cannot bridge), resulting in both wetting and 

inhibited drying. The reply was that newer formulations have been developed, which may 

address previous issues.

Q: Is better maintenance really the solution that is needed?

A: Significant disagreement amongst participants. Some point out that many water management 

problems are simple maintenance problems (clogged roof drains/scuppers/gutters, missing 

downspouts), while other argue that solutions typically applied by maintenance personnel can be 

detrimental, due to poor understanding of the building physics (application of caulking to weep 

holes, use of extensive caulking rather than repair of flashing, etc.)

Q: Since it is known that salinity is a critical parameter in the freeze thaw process, how can 

dilatometry testing capture actual thresholds similar to the field?

A: Since the samples are taken from the field in their existing condition, and they are saturated 

with distilled water (similar to the rain water that they will be seeing in the field), it is believed

that similar salinity conditions should be achieved.

Q: Has the dilatometry approach been validated with bricks from the field that were either 

confirmed to be freeze-thaw resistant or freeze-thaw susceptible?

A: Anecdotal evidence suggests that the approach is sound. Further validation would be 

beneficial.

Q: The ventilation air changes per hour (ACH) used in Mr. Ueno’s simulations seemed too high.

A: This is an item which merits further investigation, including field measurement.

Q: One retrofit option for embedded beams is to cut off the embedded beam stub, and build 

supports inboard of the masonry wall. If one does not cut the beams embedded in the masonry

(instead simply adding the supporting columns on the interior) would the rot spread?

A: It is unlikely that the rot would come that far in. However, it might be necessary to connect 

the supporting structure to the masonry with metal strapping, to avoid movement.

Q: Would borate treated sticks, like those used in telephone poles, be a simple answer to 

embedded beam problems?

A: Perhaps. There was some concern whether borate would spread sufficiently through the body 

of the wood to achieve adequate protection.

Q: Could one use a steel shoe (joist hanger) to transfer the load from the beam to the masonry in 

the case of an embedded wood beam?
22

A: Yes. Another option is a pressure treated ledger board connected to the masonry and the 

joists.

Figure 16. Steel angle bolted to masonry to transfer load out of beam pocket

5.2 Group Discussion to Cover Key Questions and Action Items

The following discussion covered some of the key questions raised in the meeting agenda.

5.2.1 Details for Bulk Water Control

What are typical details required to reduce rainwater exposure, thus balancing out reduced 

inward drying with reduced wetting from the exterior? Are typical existing surface drainage 

details (e.g., solid stone sills, window “eyebrows,” band courses) sufficient, or is it necessary to 

retrofit additional protection?

Need to examine inclined vs. horizontal surface treatments as separate issues; greatest risk lies 

with horizontal surfaces (limited drainage).

Need to examine the “funnel” effects at joints, such as at coping stones/band courses.

Need a retrofit drip edge that can be used under window sills with a minimal visible appearance 

for historic buildings. One example was to use a caulk bead to create a low-visibility drip edge 

on the underside of a window sill.

Need to understand the effect of retrofitting kerf cuts to the underside of window sills which lack 

proper drip edges (one practitioner has seen water bridging this gap, during spray tests).

Also need to address the rowlock course window sill, as seen in lower cost/residential 

construction. One possible solution is the use of a metal sill cap, across the top of the sill. But as 

a cautionary note on the sill cap: one observed problem was interior air leakage condensation on 

underside of sill cap.
23

Figure 17. Precast window sill drip edge detail (L); rowlock window sill (R)

What is the treatment required for window? Generally, the windows should be removed, the 

opening should be waterproofed, and the window reinstalled. Rehabilitation of windows in place

should be approached with caution. The use of exterior storms might reduce the wetting potential 

at the window opening; however, it typically does not address leakage between the frame and 

masonry.

One proposed water shedding detail is a gutter at the top of the window, to move water to the 

sides.

5.2.2 Thermal Issues

Do we want to use composite studs (e.g., extruded PVC “Eco Stud”) in lieu of steel studs in 

order to improve thermal performance?

Creating space between the steel stud frame wall and the masonry wall (to prevent thermal 

bridging) is always an uphill battle. The industry should clearly define the impact of various stud 

spacing levels. The minimum dimension is sufficient to avoid direct connection of the stud to the 

masonry. The ORNL Steel Stud (Modified Zone Method) online calculator can be used to 

approximate the effect of stud spacing away from the masonry wall. Additional discussions are 

needed on using non-metallic tiebacks from the framing to the masonry.

5.2.3 Interior Insulation Material Selection

Many of the projects presented here appear to be gut rehabilitations. There is a need for a system 

that insulates without requiring gutting the interior. Foam injection sounds like a sensible 

approach when trying to reduce the scope, and keep the renovation simple. However, there are 

risks of insufficient coverage, trapping moisture-sensitive materials outboard of the insulation, 

and blowing off interior finishes.

As an example of interior finish removal: one recent case had gypsum block (USG Pryobar)

infill interior to the masonry wall. Leaving this in place, outboard of the insulation creates a 

durability risk; field measurements showed high moisture contents even prior to insulation. The 

recommendation was to remove the gypsum block before insulation. Other practitioners noted 

that when gypsum plaster was “trapped” outboard of the insulation in some retrofits, it reemulsified and softened.
24

What are options besides using ccSPF and ocSPF spray foams? The industry has concluded that 

fiberglass and polyethylene is a high risk solution. However, perhaps greater success could be 

achieved with cellulose or mineral wool (greater airflow suppression and elimination of voids) 

and a variable-permeability interior vapor control layer (e.g., CertainTeed MemBrain; allows 

drying but controls wintertime condensation). However, the group had concerns about salt 

migration. One example building had sufficient moisture movement to create “salt stalactites” 

with a cellulose installation. It is a highly questionable solution in cases where there is the 

possibility of future bulk water management issues.

5.2.4 Insulation Assembly Geometry Effects

What is the impact of an air space (vented to inside, outside or unvented) for various wall 

thicknesses, both in terms of thermal effects and moisture redistribution? This is a research need 

to be addressed.

What is the effect of party demising (interior-to-interior) walls, intersecting with the exterior wall

(a.k.a. “tee” walls)? Two-dimensional thermal simulations seem to indicate that roughly 12” of 

insulation along the interior wall is sufficient to control the majority of heat flow. A common 

case would be when one unit in a multi-unit residential building was being insulated, while the 

adjacent unit was remained uninsulated.

Figure 18. Two-dimensional heat flow modeling party wall (assembly, temperatures, heat flux)

5.2.5 Energy Savings

What are the energy savings associated with interior insulation retrofits? Can effective thermal 

performance be obtained by leaving these buildings uninsulated, and relying on thermal mass 

effects? Energy models suggest thermal mass is not significant to energy performance for 

buildings located in heating-dominated climates; it is of greater benefit in locations with high 

diurnal swings around the interior setpoint (see Figure 19).

Uninsulated unit Insulated unit
25

Climate: Burlington, VT

Case 2 ≈ 60% reduction in heat flow through 

walls

Case 3 ≈ 75% reduction in heat flow through 

walls

Figure 19. Hygrothermal simulations of heat flux with uninsulated, 1.5”, and 3” ccSPF walls

However, there is an LBNL study that showed 39% energy saving by adding an extra layer of 

drywall (additional thermal mass) (Kosny). Also, thermal mass is important and valuable to 

allow off-peak heating and may be more important in the future with variable electricity supply. 

But there was agreement that leaving these buildings uninsulated is not a good choice for energy 

performance.

5.2.6 Durability Issues

What is the current level of understanding of evaluating the in-service post-retrofit freeze-thaw 

resistance of a masonry enclosure, using material property testing and hygrothermal simulations? 

Can this process be developed further, and/or streamlined?

What are effective solutions to address durability concerns at moisture-sensitive structural 

members (e.g., wood beams and joists) embedded in masonry structures, in a post-retrofit 

situation?

In Germany, it is estimated that in roughly 30% of cases, there are problems with inset wood

(Künzel). Other than adding heat to the beam ends, there are no clear solutions. Fraunhofer has a 

project underway monitoring beam end moisture contents.

There was a suggestion that the beam be set in a clay plaster, but there is little actual experience

with this technique.

Q: Are there cases of building enclosure failures (specifically freeze-thaw damage to the 

masonry) that can be traced directly to the retrofit of interior insulation, and what were the 

circumstances and contributing factors in the failures?

A: Actual cases with modern insulation are not known. t is easy to confuse damage due to 

surface water management issues.

5.2.7 Historic Issues

What are some key issues that need to be addressed when interfacing with historical preservation 

requirements (e.g., National Park Service tax credits) and performing these retrofits? (Left open.)

5.2.8 Capillary Flow and Efflorescence

Are there retrofit methods to reduce capillary uptake through existing masonry structures, which 

are simpler (and less costly) than the retrofit of regletted capillary breaks? Specifically, how do 
26

we reduce capillary flows through foundation walls, which can result in salt efflorescence of the 

masonry, and/or failures of the exterior parging.

There are “damp proof cremes" available commercially in the United Kingdom, which are 

injected into horizontal holes in order to create a “damp proofing course’ (Figure 20). Are these 

viable products? They are reported to work only 20%-30% of time in the field (Künzel).

Figure 20. Installation of injectable liquid damp-proofing course (Aida DPC, Remmers Ltd., 2005)

Special salt-accommodating plasters have been used for the last 30 years in Germany; they work

well and are inexpensive. The plasters function by having substantial interstitial of space, where 

salts can crystallize without causing dimensional instability issues. Saw cut reglet damp proofing 

is an option, but special plasters are much less costly (Künzel).

It was noted that the rate of capillary transport is a function of temperature; it is greater in cold 

conditions than warm (Rose). This may be a significant phenomenon, and may be affected by 

addition of insulation.

Nitric salts are very hygroscopic, which also leads to substantial efflorescence in agricultural 

applications, and may be throwing off Rose’s observations (Künzel).
27

5.2.9 Non-Specialist Analysis

Based on hygrothermal simulations and field experience, are there widely-applicable limits to 

interior insulation levels (and type of insulation), based on climate zone, building exposure, and 

material properties that can be evaluated by non-specialists? (Left open.)

5.2.10 Tapered Window Openings

Given that many mass masonry buildings have deep window openings with limited available 

space (due to window clearance issues and historic requirements not to change window profiles), 

what is the effect of thinner (e.g., ~1”) insulation at these openings?

Tapered window opening and exposed window sills limit ability to add insulation. No available 

solutions were presented. Two- or three-dimensional thermal modeling would provide some 

insight into this issue.

Figure 21. Tapered window opening jamb detail and interior view (sill left uninsulated)

5.2.11 Experiment and Monitoring Opportunity

Fraunhofer Center for Sustainable Energy Systems in Cambridge, MA is moving to an old 

masonry (brick) building, and they are open for experiment insulation methods and monitoring 

installations. Please contact Dr. Kosny if interested in participating in this work.
28

References

Lstiburek, J.W. (March 2010a). “Building Sciences: Rubble Foundations.” ASHRAE Journal

(vol. 52); pp. 72-78. Atlanta, GA: American Society of Heating, Refrigeration, and AirConditioning Engineers, Inc.

Lstiburek, J.W. (May 2010b). “Building Sciences: Thick as a Brick.” ASHRAE Journal (vol. 

52); pp. 50-56. Atlanta, GA: American Society of Heating, Refrigeration, and Air-Conditioning 

Engineers, Inc.

Mensinga, P., J. Straube, C. Schumacher, C., et.al. 2010. “Assessing the Freeze-Thaw Resistance 

of Clay Brick for Interior Insulation Retrofit Projects” Performance of the Exterior Envelopes of 

Whole Buildings XI. Atlanta, GA: American Society of Heating, Refrigeration, and AirConditioning Engineers, Inc. Proceedings of Building XI Conference Clearwater, FL.

Pettit, B. (April/May 2008) “Remodeling for Energy Efficiency.” Fine Homebuilding Magazine. 

Newtown, CT: Taunton Press.

Straube, J.F., and Burnett, E.F.P., (2005). Building Science for Building Enclosure Design, 

Building Science Press: Westford, MA.
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Appendix A (Agenda, Objectives, Key Questions, Presenter Bios)

Building America Expert Meeting on

Interior Insulation Retrofit of Mass Masonry Wall Assemblies

Date/Time: Saturday, July 30, 2011

9 am to 3 pm

Location: Westford Regency Hotel

219 Littleton Road Westford, MA 01886

P: (800) 543-780; (978) 692-8200

Meeting Manager: Kohta Ueno, Building Science Corporation

Kohta@buildingscience.com; (617) 863-5276

List of Presenters:

• John Straube (Building Science Corporation)

• Henri Fennel (Conservation Services Group)

• Mark Bomberg (Syracuse University)

• Christopher Schumacher (Building Science Corporation)

• Kohta Ueno (Building Science Corporation)

The objective of this session is to explore the current state of implementation and research on 

interior insulation retrofit of mass masonry wall assemblies. There is a large stock of uninsulated 

mass masonry buildings and the retrofit of interior insulation is commonly implemented to 

improve their energy performance, while maintaining their often historic exterior appearance.

There are known durability issues associated with interior insulation, such as interstitial 

condensation and freeze-thaw damage issues. These issues have been or are being addressed in 

many cases, but there are still remaining questions that should be answered before mass 

implementation in a variety of climate zones. However, leaving these buildings uninsulated is at 

odds with the Building America target of broad energy retrofits of existing homes to reduce 

residential carbon emissions 20% by 2020 and 80% by 2050. Discussions on this topic will be 

applicable to existing mass masonry single and multi-family residential buildings. Issues such as 

durability, energy performance, and detailing will be examined.

Key questions regarding this meeting:

1. What are typical details required to reduce rainwater exposure, thus balancing out 

reduced inward drying with reduced wetting from the exterior? Are typical existing 

surface drainage details (e.g., solid stone sills, window “eyebrows,” band courses) 

sufficient, or is it necessary to retrofit additional protection?

2. What are the energy savings associated with interior insulation retrofits? Can effective 

thermal performance be obtained by leaving these buildings uninsulated, and relying on 

thermal mass effects?

3. What is the current level of understanding of evaluating the in-service post-retrofit 

freeze-thaw resistance of a masonry enclosure, using material property testing and 

hygrothermal simulations? Can this process be developed further, and/or streamlined?
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4. What are effective solutions to address durability concerns atmoisture-sensitive structural 

members (e.g., wood beams and joists) embedded in masonry structures, in a post-retrofit 

situation?

5. What are some key issues that need to be addressed when interfacing with historical 

preservation requirements (e.g., National Park Service tax credits) and performing these 

retrofits?

6. Are there retrofit methods to reduce capillary uptake through existing masonry structures, 

which are simpler (and less costly) than the retrofit of regletted capillary breaks?

7. Based on hygrothermal simulations and field experience, are there widely-applicable 

limits to interior insulation levels (and type of insulation), based on climate zone, 

building exposure, and material properties that can be evaluated by non-specialists?

8. Are there cases of building enclosure failures that can be traced directly to the retrofit of 

interior insulation, and what were the circumstances and contributing factors in the 

failures?

9. Given that many mass masonry buildings have deep window openings with limited 

available space (due to window clearance issues), what is the effect of thinner (e.g., ~1”) 

insulation at these openings?

Expected Results:

As a result of this meeting, a summary report will be prepared and peer reviewed before final 

submission and web posting. It is expected that the information obtained, relative to the Key 

Questions listed above, will lend itself toward the eventual production of an important guide for 

best practices for interior insulation retrofit of mass masonry wall assemblies.

Invitees:

Participants will be key people working in the fields of building science, building enclosure 

research and consulting, residential construction, and building energy efficiency. A blend of 

industry, research, and government participants will be sought.

Meeting Agenda:

• 9:00 AM Welcome and Meeting Introduction: Brief Building America Program 

Overview

• 9:15-10:00 AM John Straube: Mass Masonry Insulation Retrofits: Fundamentals and 

Challenges

• 10:00-10:30 AM Henri Fennel: Variations on a (Mass Masonry?) Theme – With A Touch 

of Foam

• 10:30-10:45 AM Break

• 10:45-11:15 AM Mark Bomberg: Thermal Upgrade of Masonry Walls -Interior Methods

• 11:15-11:45 AM Christopher Schumacher: Assessing the Freeze-Thaw Resistance of 

Clay Brick for Interior Insulation Retrofit Projects
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• 11:45-12:15 AM Kohta Ueno: Masonry Wall Interior Insulation Retrofit Embedded 

Beam Simulations

• 12:15 to 1:15 Lunch break (lunches provided)

• 1:15 to 1:45 Special Topic Discussions

o Field experience of field practitioners not on speakers list

o If warranted—collect photos for display and discussion over lunch break from 

field practitioners

o Discussion of problematic water concentration details seen in the field

o Discussion of retrofit details to reduce water exposure

• 1:45 to 3:00 Group discussion to cover key questions, action items, follow-up plan, and 

wrap-up.

• 3:00 PM Adjourn meeting

Presenter Bios

John F. Straube (Ph.D., P.Eng.) is a principal of Building Science Corporation and a professor of 

building science in the Civil Engineering Department and School of Architecture at the 

University of Waterloo, Canada. Dr. Straube has acted as an educator, researcher, consultant and 

expert witness on energy efficiency, durability and IAQ. Current interests include the optimal 

system design of buildings, sustainable buildings, and moisture problem avoidance.

Henri Fennell (CSI/CDT) is a principal of HC Fennell Consulting, a building science consulting 

and education firm. He is an architect with twenty-five years of experience in energy 

conservation products and services, and specializes in the use of manufactured and fieldinstalled urethane technologies. As a building envelope consultant, Henri worked with architects, 

designers, builders, and contractors to diagnose and solve building envelope problems. Before 

this position, he was president of Building Envelope Solutions, Inc. / FOAM–TECH, a spray 

foam contracting firm, and then Technical Research Manager at Conservation Services Group, 

Inc.

Mark Bomberg (Ph.D.) is a research professor at Syracuse University. He is a leader of an 

industry-university collaborative research center on hygrothermal performance of building 

enclosures. His research specialties include high performance building enclosures and thermal 

insulating materials. Prior to this position, he was a senior researcher at the National Research 

Council of Canada for 24 years.

Christopher J. Schumacher (M.A.Sc.) is a principal of Building Science Corporation. He is 

recognized as an expert in the field of building monitoring and building systems and enclosure 
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testing. He has led the design, installation and analysis of monitoring systems for 15 building 

enclosure test facilities, six test building sites, three climate chambers and two sustainable 

building technologies demonstration projects in over a dozen states and countries as

far abroad as Mongolia and New Zealand.

Kohta Ueno (M.A.Sc.) is a senior associate of Building Science Corporation. His responsibilities 

at Building Science Corporation include project management, liaison work with builders and 

industry clients, HVAC design, energy analysis of house designs, computer modeling, field 

testing and verification, and forensic field investigations. He has been with BSC since 1998, and 

completed his Master’s degree with the Building Engineering Group under John Straube at the 

University of Waterloo in 2007.
DOE/GO-102012-3475 ▪ February 2012

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