Insulating Residential Masonry Buildings in Cold Climates
Most professionals now agree that masonry buildings in cold climates should be insulated. Here's how it's done.
While there are still some professionals who question the practice, or think that it is unnecessary, most professionals agree that in cold climates, a masonry residential building should be insulated. Over the years, as insulation products and installation techniques have improved, building owners and professionals have voiced concern about damage to masonry in existing structures in cold climates, and indoor air quality (IAQ) and mold growth in all climates. There are good reasons to insulate a residential building in cold climates. Well installed insulation saves money on energy; it increases occupant comfort; and it reduces our dependence on fossil fuel—which lessens the building’s impact on the environment and reduces the chance of war.
Insulating a building is one critical part of the entire-system approach to making buildings that are energy efficient—an approach that must also include well-designed mechanical systems and wise management of light, heat, air, water vapor, and liquid water within the enclosure. All these things are interrelated—so interrelated that it is difficult to talk about insulation separately. But insulation deserves its day in the sun. Learning how to insulate masonry structures properly has informed the aesthetics of my work, as well as the performance of the buildings that I have designed.
All insulations help buildings manage heat loss and heat gain through the enclosure, but some insulations can do more than one job. Spray urethane foam, for instance, can manage heat, liquid water, and vapor, making best use of materials, space, and money. Choosing the appropriate insulation level and the appropriate installation technique is a creative and scientific process. The right choice now will prevent problems in the building enclosure later. Money spent on insulation is money saved on mechanical systems. Smaller heating and cooling loads can be met with minimally sized and unconventional equipment. Good work with a system approach can provide a solution that is cost and resource efficient, life enhancing, and aesthetically pleasing.
This article describes how I have dealt with questions concerning the insulation of residential masonry buildings. I am an architect practicing in New York City. My firm designs buildings, both adaptive reuse and new construction. In partnership with Henry Gifford, mechanical system designer, we use a system approach to design high-performance buildings that can be built for the same price as standard construction. Two articles by Henry Gifford documenting some of our designs have been published in Home Energy, and Henry Gifford has contributed other articles about designing mechanical systems to improve comfort, reduce energy use, and save money (see “Third Street,” HE Sept/Oct ’05, p. 24; “Copper and Cast Iron,” HE May/June ’07, p. 6; and “Elevator Energy Use,” HE Jan/Feb ’10, p. 40). We specialize in designing apartment buildings, but construction has begun on our first hotel, an 80-unit building located in the Bronx. We also design offices, artist lofts, art studios, and industrial art production facilities that require special attention to the enclosure, to ensure strict interior climate and ventilation control. All of these buildings are urban, are built of masonry, and need insulation to meet performance requirements.
Masonry is an ancient material, one that has been used by many cultures in many different ways. Masonry can be described as units of clay, mud, stone, or concrete that can be stacked and joined to form a larger whole. The variations in color, texture, and unit size give it great appeal. Most masonry in the Northeast is joined together with mortar, and there is an important relationship between the mortar and the units: They must be matched appropriately to bond well and to provide strength and flexibility for a given design. In the Northeast, where I work, most masonry buildings are brick, but some buildings are built of brick faced with stone; others are faced with brick and backed up with terra-cotta blocks. New construction is primarily block with different materials used as facing, including brick and stone.
Masonry has been highly valued throughout history for its thermal properties. Masonry can absorb and release heat under certain conditions. Many cultures in hot-dry climates have developed ways to build with masonry that exploit this quality. For example, mud block buildings, such as adobe, absorb heat during the day and release the heat at night, resulting in warm interiors throughout the night and cool interiors throughout the day. In cold climates masonry buildings cannot absorb and release enough heat from the sun to maintain comfort. Heat must be added to make the interior comfortable. In cold climates masonry can maintain stable interior temperatures if it is protected from heat gain and loss by earth or insulation that is installed on the exterior surface of the masonry wall.
Insulating a Masonry Building
To keep a building at a stable, comfortable interior temperature in the winter, heat must be added to the building interior at the same rate at which it is lost. Heat loss includes (1) loss through the enclosure, (2) loss through the ventilation process, and (3) “loss” when energy is needed to temper cold air infiltrating the building.
To keep a building at a stable, comfortable interior temperature in the summer, heat must be removed from the building at the same rate at which it enters. Heat gain includes: (1) gain through the enclosure; (2) gain through the ventilation process; (3) gain due to infiltration air; (4) gain due to the heat given off by living things, machines, electronic devices, and lights; and (5) “gain” due to the removal of moisture that is condensed out of the air during the A/C process.
The role of insulation is to manage heat loss or gain through the enclosure. Heat moves from warm to cold. Insulation slows the rate of that movement. For most building types, and in most climates, insulation helps to reduce the amount of energy needed to maintain a stable interior temperature.
Fifteen years ago, when I opened my practice, the standard insulation technique in New York City was to install metal studs on the interior surface of exterior walls, insert fiberglass batts between the studs, and cover the batts with a finish application of gypsum board. A vapor barrier was usually included; consisting of polyethylene (poly) sheeting installed over the insulation, or the foil or treated-paper facing of the fiberglass batt. Practitioners felt that they were doing a good job and meeting code with this technique. Sadly, testing has shown that what we believed to be an R-13 wall assembly was actually closer to R-8. The R-value of the assembly was seriously diminished by thermal bridging through the metal studs, and by the inability of fiberglass batts to completely cover the surface of the exterior wall, where studs, pipes, and wires interrupt the insulation.
Mechanical system designers typically oversize their heating and cooling systems, so a shortfall in anticipated R-value would not produce occupant complaints (or lawsuits!) that could alert the designer to the problem. And ironically, since the insulation performed so poorly, nobody was concerned about the health of the masonry, because the lack of R-value allowed almost as much heat to flow through the walls as it did before the insulation was installed.
In 1996 I was introduced to the fantastic work of Maureen Davlin of the Illinois Department of Consumer Affairs, and Chicago architect Paul Knight of Domus Plus (see “Green Products Brighten Multifamily Rehab,” HE Nov/Dec ’00, p. 34). In Chicago, Paul and Maureen, with the help of Joe Lstiburek, now a principal at Building Science Corporation, were innovating the Airtight Dry Assembly (ADA) technique for substantial gut rehab of masonry buildings. They were getting compelling results in energy reduction, comfort, health, and safety from their work. The technique consisted of incorporating an air barrier (an interior shell), built from the gypsum board that was already part of the interior renovation design, into the wall assembly and installing a continuous blanket of cellulose insulation in the cavity between the exterior wall and the air barrier. They tried many different types of insulation, including wet-spray and dense-pack cellulose, spray mineral wool, and spray fiberglass. They worked with poly vapor barriers, foil-faced gypsum board, and vapor-retardant paints.
Observation of their work, study of the building science principles behind it, and a good working knowledge of the New York City code led me to believe that ADA and spray cellulose could work well in New York City for adaptive reuse. In 1998 I started specifying a wall assembly for masonry buildings comprised of 2⅝-inch metal studs at 16 inches on center (OC), front face of the studs 4 inches or 5 inches (depending on the construction budget) out from the interior face of the existing masonry wall, covered in ⅝-inch gypsum board. The gypsum board was carefully sealed with caulk to the subfloor at the base of the wall, brought up between the wood joists to the underside of the subfloor above, and sealed. Dry cellulose insulation was then blown into the 4-inch or 5- inch cavity at 3 ½ lb per square foot density, giving a true R-14 or R-17.5. For the vapor barrier I used flat wall paint, nothing else! All holes in the ADA were sealed. Since 1998 I have insulated 49 buildings with this specification. Eighteen of them were the first buildings to receive ADA air barriers and cellulose insulation in New York City. The work was documented in the Real Estate section of the New York Times in November 1998 and has continued to inspire the energy-efficient building community.
Don’t Be Afraid!
Not long into my practice of insulating masonry, I started to get a reputation with a contingent of Canadian building scientists who were warning builders and contractors against insulating masonry. In fact, I was known as “the architect from New York who insulates masonry” for quite few years! The Canadians came by their concerns honestly (although to date I have yet to see a masonry building destroyed by insulating it). Their argument was as follows:
- In a cold climate, when an existing masonry wall is insulated on the inside, the wall gets much colder in the winter. Before the wall was insulated, interior heat moved rapidly through it to the exterior, keeping the wall warmer.
- If the wall is wetted by rain, some of the rain will shed down the face of the wall, but some of it will stick to the surface of the wall and be absorbed. Sun shining on the wall will drive this water in the form of vapor deeper into the masonry. With insulation, energy is moving through the wall at a slower pace, which in turn will slow the rate of drying, and the wall will remain wet longer.
- Freeze/thaw cycles may cause cracking in the masonry because walls remain wet longer, as per above.
These are serious issues. Why am I not worried about my insulated walls?
- As part of the scope of my work I make sure that the wall is pointed and in good repair.
- The building is thoroughly assessed for any damage to bricks and mortar inside and out. Cracks, crumbling of the surface of the brick, visible moss and spotting, and efflorescence and signs of subflorescence are all scoped for repair. If a building is showing any problems with liquid water management, these problems must be resolved prior to insulating. Conditions such as crumbling of the surface of the brick, which may indicate subflorescence, must be thoroughly understood and remedied.
- I make sure that all of the materials in the wall are vapor permeable, and that wetting can dry to the inside or the outside of the building, depending on the direction of vapor drive.
- Vapor will move from warm to cold, but also from more to less—the permeability of my wall does not inhibit this action.
In order for freeze/thaw cycles to cause cracking in masonry in good condition, times of severe prolonged wetting must coincide with times of severe prolonged freezing. This does not occur in my climate zone.
A careful look at New York weather data shows that severe prolonged wetting and freezing do not coincide. Look carefully at the data for your own climate before you decide to insulate; but it is generally accepted now that insulation can be applied to the interior of a masonry wall that is in good condition throughout the Northeast and into Canada, without running the risk of freeze/thaw damage. When in doubt, hire a professional to run software model of your situation using WUFI. The software will run a year’s climate data, and it is possible with the software to see how the wall behaves under typical moisture and temperature conditions for the year. You will need to know the construction of your wall, the type of masonry and mortar, and your location.
There are other serious issues to be aware of when insulating on the inside of masonry walls in cold climates. The interior surface of an insulated masonry wall will be colder in the winter than it would be if the wall were not insulated. How much colder it will be depends on the R-value of the insulation. The higher this R-value, the colder the masonry wall will be outboard of it. Moisture in warm interior air can condense on cold surfaces within wall assemblies. This may or may not cause problems in the wall. Condensation on the brick may be absorbed into the brick and dry with no problem. If cellulose insulation is used, the cellulose may absorb and distribute the moisture. Conversely, enough vapor may build up to cause freeze/thaw efflorescence or subflorescence in the wall, or to rust metal framing, or to deteriorate the wood studs and the subfloor in the cavity. I find it best to avoid these possibilities by making sure that the ADA is installed to act as an air barrier. Warm interior air can’t reach the cold surface with the air barrier stopping it, and while a small amount of vapor will diffuse through the gypsum board, it will not be enough to damage the materials in the wall. Avoiding condensation in the wall by installing an air barrier, and using vapor-permeable materials in the wall that can act to distribute water vapor and promote drying, are two of the best ways to control mold growth and deterioration in interior-insulated masonry walls.
Here are some other ways to insulate masonry on the interior using an air barrier:
- A thin spray of urethane foam can be applied to the masonry to act as an air barrier. Other insulation is then applied inboard of the spray foam.
- A thicker spray of urethane foam can be applied to the masonry to act as an air barrier and as insulation. The urethane foam is the only insulation in the wall.
- Board foam can be applied with adhesive to the inside of the masonry wall to act as an air barrier and as insulation. The joints are taped, transitions to floor and ceiling are caulked, and stud framing is built inboard of the foam for installation of the interior wall finish.
- A new material called Aerogel can be laid directly onto the exterior walls to act as insulation. A plaster top coat is applied to act as interior finish and interior air barrier.
- Urethane foam can be injected into thin cavities between the exterior masonry and plaster on lathe finishes.
Remember: It is extremely important that the masonry walls be in great shape, with no cracks that allow water penetration. If you can’t solve the moisture or water problem, do not insulate the wall on the interior in a cold climate.
Turning the Wall Inside Out
Insulating masonry on the inside of the building is an appropriate solution under many circumstances, but it has limitations. Some existing buildings are full of wonderful interior detail, making insulation difficult or impossible to install. Owners may want exposed masonry on the interior. Tenants may be in place and cannot be moved to do an interior insulation job. Space may be limited on the interior, especially in urban buildings. Or there may be water problems that can be solved only by installing a new exterior cladding. In these cases, it may be worthwhile to consider installing the insulation on the outside.
For new buildings built with block, installing insulation on the outside of the masonry is the only strategy that should be used. Here are some of the benefits of insulating on the outside of a masonry wall:
- In the winter, the interior surface of the wall will be the same, or much the same, temperature as the interior air, and condensation will not occur because the wall is warm.
- In the summer, any condensation that occurs will occur on the exterior side of the masonry wall.
- The thermal mass of the wall will be inboard of the insulation, allowing it remain thermally stable, summer and winter.
- Insulation can be installed continuously, uninterrupted by floor construction, pipes and wires, and studs. This will give the wall a true and uniform R-value, with no thermal bridges.
- Cladding an existing wall, especially one with severe or unsolvable water problems, can extend the useful life of the building.
- Cladding an existing building can give it an exciting new identity.
- None of the problems described earlier in this article—damage to the masonry, condensation, and mold growth—will arise.
- With proper detailing on new construction, exterior insulation can continue down the wall below grade to the footing, forming a continuous thermal layer.
Recently I served on Mayor Bloomberg’s task force for greening New York City’s building code, and I had a chance to suggest code language that will facilitate large-scale economical implementation of exterior insulation. The measures I generated are still under review, but I hope to see them successfully adopted. They address the following two points:
- Discounting insulation thickness square footage from allowable zoning square footage, so that the owner gets the square footage of the insulation back as usable square footage in the building. Given New York City real estate values, this measure will pay for the insulation!
- Allowing a thickness up to 6 inches of exterior insulation to be added to existing buildings at the front wall property wall without a penalty for stepping over the property line into the street, and at legal side yard walls and rear yard wall without penalties for stepping into required zoning depths for side yards and rear yards.
Since 2001 I have focused on studying how to install insulation on the outside of block walls economically and efficiently. I have done so because I see the how much this can improve the performance and the aesthetics of the building. My firm has developed many ways of doing this. Some have been constructed, some are on the boards and will be installed on buildings shortly, and some have been discarded. Insulations we have looked at include mineral wool; exterior insulation and finish system (EIFS) assemblies; extruded polystyrene (XPS); expanded polystyrene (EPS); polyisocyanurate; Aerogel; and spray urethane foam. My work on this continues to evolve.
Here are short descriptions of the buildings I have worked on so far.
227, 228, and 299 East Third Street and 242, East Second Street, Manhattan, New York
These four new-construction apartment buildings are built with block and insulated with mineral wool outboard of the block. The insulation is covered with a finished façade that includes a brick veneer with precast concrete sills, lintels, copings, and stringer courses.
491 Fletcher Street, Bronx, New York
Portions of this new-construction building are built of block with mineral wool outboard of the block and covered with a finished façade of ⅜-inch wood composite and resin panels. Other parts of the building are sheathed with EIFS, with precast sills specially designed to manage water away from the façade. Exterior insulation is continuous from the footings, up the walls, over the parapets, and onto the roof surface.
803 Knickerbocker Avenue, Brooklyn, New York
This new-construction apartment building is built of block sheathed with EIFS in wedge shapes; the wedges also provide shading from the summer sun. The EIFS wedges are 3–12 inches thick, with an average R-value of 30. Other parts of the block structure are sheathed in 2½ inches of polyisocyanurate and a ½-inch-thick brick veneer, yielding a continuous R-value of 18.5. Exterior insulation is continuous from the footings, up the walls, over the parapets, and onto the roof surface. Insulation is also installed under the cellar floor slab. This building is designed to conform to the German Passive House standard. Construction will start in spring 2010.
35 Bartlett Street, Brooklyn, New York
This new apartment building, currently in the design phase, will meet the German Passive House standard. Exterior insulation techniques currently under consideration for this building include a sculpted façade design featuring EIFS and brick veneer over polyisocyanurate. Construction will begin in early 2011.
I have discovered through my work that insulation is something to get really excited about. We live and work in interesting times. As architects with a good building science education, we can successfully practice ancient and modern techniques to make the most of our resources, while providing wonderful new experiences for those who interact with our building designs.
The Office of Chris Benedict, R.A. provides architectural services for commercial and residential buildings. Chris Benedict’s unique understanding of buildings and mechanical systems allows her to rethink and invent elegant holistic solutions to building design. Her firm specializes in buildings that are healthy, durable, and energy efficient, built for the same price as typical construction.
For more information:
E-mail the author at firstname.lastname@example.org.
To learn more about the ADA technique, go to the Building Science Corporation’s Web site, www.buildingscience.com/index_html. In the search box, write “air tight drywall assembly”.
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