musingsheader image
6 Helpful?

Insulating Old Brick Buildings

If you’re thinking of insulating the interior of a load-bearing brick wall, proceed with caution

Posted on Aug 12 2011 by Martin Holladay

UPDATED March 19, 2015

Older buildings with load-bearing brick walls are common in many northern U.S. cities. While these thick (muti-wythe) brick walls were often plastered on the interior, they were rarely insulated.

Load-bearing brick walls are tricky to insulate. Here’s why: if you insulate the wall on the interior, you’ll make the bricks colder during the winter. As we know from the psychrometric chart, cold bricks are always wetter than warm bricks. Once the wall is insulated, the escaping heat that formerly passed through the bricks is no longer available to drive out the moisture. So your wet bricks stay wet for a long time. In some cases, repeated cycles of freezing and thawing can permanently damage the bricks, causing them to fall apart.

After I began researching and writing this article, I received an invitation to attend the Department of Energy's Expert Meeting on Interior Insulation Retrofit of Mass Masonry Wall Assemblies, held on July 30, 2011 in Westford, Mass. (The meeting was sponsored by the Building America program.) The presenters at that meeting — John Straube, Henri Fennel, Terry Brennan, Bill Rose, Mark Bomberg, Christopher Schumacher, and Kohta Ueno — all contributed valuable information that helped with this article.

It’s possible to insulate a brick building on the interior

If insulating a brick wall on the interior can make the wall vulnerable to freeze/thaw damage, does that mean such walls should never be insulated? No. But builders who want to insulate an old brick wall should proceed cautiously.

There are no simple rules of thumb when it comes to assessing the vulnerability of an existing brick building to freeze/thaw damage. However, here are the most important points to remember:

  • Most, but not all, existing brick buildings can be safely insulated on the interior.
  • The colder the climate, the greater the risk of freeze/thaw damage.
  • The thicker the insulation, the greater the risk of freeze/thaw damage.
  • The more rain that falls on the wall, the greater the risk of freeze/thaw damage.
  • Some bricks are more vulnerable to freeze/thaw damage than others; there are tests to determine whether your building has good bricks or bad bricks.
  • If you insulate the interior of a brick building, the ends of joists and beams that are embedded in the exterior walls can rot.
  • The first step in assessing the vulnerability of any brick building to freeze/thaw damage is a site visit by a smart observer.
  • If all of this sounds complicated and confusing, you may want to hire a consultant to help you determine the best way to proceed.

The best strategy is to insulate on the exterior

There is a simple way to avoid all of the problems listed above: just insulate your brick building on the exterior. (For more information on this option, see Deep-Dish Retrofits.)

One exterior-insulation approach involves covering brick walls with EIFS — that is, a layer of rigid foam covered with synthetic stucco.

“Exterior retrofit is the preferred building science solution,” says John Straube, a principal at Building Science Corporation in Somerville, Massachusetts. “It’s a great solution for ugly buildings.”

Of course, most owners of historic brick buildings are reluctant to cover up their bricks. As Terry Brennan, the president of Camroden Associates in Westmoreland, New York, explains, “If you can’t do the smart thing — insulate on the outside — then you have to do other smart things to enable you to do the silly thing — that is, to make insulating on the inside work.”

Hiring a consultant

Because of all the uncertainties associated with insulating brick walls, many building owners hire a consultant to advise them. Rather than trusting your neighborhood architect, it’s best to invest in a consultant who specializes in such projects. “The most important thing and the cheapest thing an owner can do is to get Building Science Corporation to send one of our guys to the job site to look at the building,” says Straube.

According to Brennan, “It’s definitely worth hiring an expert, but remember: the experts are still learning.”

Inspecting the building

Don’t assume that the first step in this process is getting your bricks tested. Using a sharp set of eyes, the first step is to inspect the building. “Walk around and look,” says Straube. “Look for stains and rot. Talk to people who have been in the building. Ask them if it has been leaking.”

A humble inspector will speak little and listen much. “The site visit is the most important thing we can do,” says Straube. “Walk around the exterior and interior. The information you gather is invaluable. Look for wetting patterns, signs of erosion. Look where dust is accumulating. Look for rain leaks. Open up walls and look inside of them. Put a hole in the wall — bash some holes in the wall with a hammer. Look at the bricks at grade. Look below windows. Look for freeze/thaw damage. Look at unused chimneys. If the parapet is in good shape, that’s a good sign.”

Since the bricks in unused chimneys and parapets don’t benefit from the heat that usually flows through walls, they act as tell-tales. “You walk around the building, and you notice there is an unused chimney integrated into the exterior wall,” says Straube. “So you ask, ‘How many years has the chimney been not been in use? Oh — twenty years?’ These are bricks in the most exposed part of the building, with no heat flowing through. That’s what I call a full-scale test. Maybe it turns out that this brick in this situation is quite tolerant. If you have tall parapets, they get twice as much rain and no heat flowing from the inside — especially if the parapet is tall. The taller it is, the less heat it sees. In other cases, you might have a building that has been left abandoned, or kept at 40 degrees.” In all of these cases, the bricks have been cold and exposed to freezing weather for years. If they are in good shape, you will probably be able to insulate the building.

“If there are splotches on the bricks away from concentrating rainwater, if you see flaking, then you can tell that the brick is already failing, and you are on the edge,” Straube continued. “Or perhaps you are looking at an in-between case — a building with no parapets or chimneys, where maybe you see some damage at the window corners, some signs of drooling. Maybe there is some metal flashing on the window sills from the last time the windows were replaced, and all the flashing does is direct water to the ends where it dribbles on the walls. Then maybe you see freeze/thaw damage. So now the question is, ‘Can we design water-shedding details that help us step back from the edge?’”

Terry Brennan described a building in Utica, New York, that had problems after it was insulated. “It showed signs of failure after 3 or 4 inches of foam was sprayed on the inside of the 3-wythe brick wall,” Brennan told me. “The building had a bunch of stupid detailing: some projections like gargoyles, as well as a cast-concrete projecting shelf. The rain landing on the coping directed all of the water to the outboard edge, which ends at a mortar joint. The walls were wet. That’s stupid. However, the building didn’t fail until it got spray-foamed, because it was able to dry out. But once it was insulated, the building had bad freeze/thaw damage in just two years. It failed because it’s located in a cold climate and the building had really stupid detailing.”

Deal with the rain

The moral of the story is: If you aren’t willing to manage bulk water issues, don’t bother to insulate your brick building. “You need to deal with the rain,” says Brennan. “You need to do everything you can to keep the rain off the wall. If there are ledges, you want copper flashing to shed it off the ledge — flashing with a projecting drip-edge.”

Building scientist Joseph Lstiburek agrees. “You can insulate walls to a great extent if water isn’t concentrated on the surfaces,” says Lstiburek. “So the first thing that you do before you do any insulation is you install your drip edges, you deal with your flashings, you deal with the rain shedding things that will basically kick the water off of the surface.”

Assess the bricks

Bricks vary. Lstiburek says, “Some brick is really bad, some brick is pretty bad, some brick is pretty good, and some brick is great.”

At the Building Science Corporation, John Straube and Chris Schumacher have been researching which types of tests are most useful. They have developed a testing protocol to determine the thermal conductivity and freeze resistance of bricks. “We now have a test method that allows us to look at the load and the response of the materials,” says Chris Schumacher. “There is a critical degree of saturation at which freeze/thaw damage occurs. You can test the brick to quantify the point at which the material fails. You want to establish a limit for moisture content during freeze/thaw.”

Don’t assume that all of the bricks in your building are identical. “The best bricks were often used on the exterior,” notes Straube. “If I take a brick sample from the exterior, it may be different from the brick sample from the interior.”

Although it’s a good idea to test bricks from all of the wythes in the wall, the inner wythe is often the most crucial one to test. “After you insulate, the biggest change is in the interior side of the masonry,” says Straube. “The outer wythe has always been cold in winter, but now the inner wythe might for the first time flirt with 32 degrees or lower in some climates.”

Hygrothermal modeling

Once your bricks are tested, you’ll have a good idea of their vulnerability to freeze/thaw damage. You’ll also have some values that can be plugged into a hygrothermal modeling program like WUFI.

However, few energy consultants are WUFI experts. Users of WUFI must be careful of the “garbage in, garbage out” problem. When it comes to WUFI, remember: don’t try this at home. “WUFI modeling can guide decision making,” says Straube. “But WUFI modeling requires knowledge, comparison to measured data, and real experience.”

Climate matters

WUFI modeling uses climatic data to model moisture and thermal flows through building assemblies. In general, brick walls in cold climates are more susceptible to freeze/thaw problems than brick walls in warm climates.

“It’s rare that we have to worry about freeze/thaw problems in places like New Jersey and New York City,” says Lstiburek. “I don’t think we have much to worry about in Boston. But I’d be real nervous in Burlington, Vermont, and I’m real nervous in Ottawa, and I’m kind of semi-nervous in Toronto. … When we start getting into, say, Portland, Maine, I’m going to say you probably shouldn’t insulate more than R-10.”

One more worry: embedded beams and joists

The exterior walls of many old multi-wythe brick builders are used to support beams and joists. If the building is insulated on the interior, the ends of these embedded beams get colder — and therefore wetter. Moreover, less energy is available to help them dry out.

“Embedded wood timbers can rot,” says Straube. “Wood and steel are both moisture-sensitive. If steel corrodes, it expands — and that is a problem. There are a number of techniques to address embedded beams. You can inject the wood with borateBoron-containing chemical that provides fire resistance to materials such as cellulose insulation and provides decay and termite resistance to wood products. Borate is derived from the mineral borax and is benign, compared with most other wood treatments. salts to preserve the wood. You can insert metal wedges to conduct heat to the end of the beam. You can install hot water pipes to heat the end of the beam. Finally, there’s the practical Yankee solution: you build a load-bearing wood wall to support the beam, and then you fire up your chainsaw and cut off the end of the beam.”

Almost all of the solutions to the embedded beam problem have drawbacks except the chainsaw solution.

What type of insulation? And how thick?

Most people assume that you need thicker insulation in a cold climate than a warm climate. While that makes sense for wood-framed buildings, it isn’t necessarily true for an old brick building. In general, brick buildings in cold climates get less insulation than buildings in warm climates. (Thinner insulation allows more escaping heat, keeping the bricks a little warmer and safer. Moreover, in some cases, thin insulation can allow some drying to the interior.)

“So the question is, ‘Well, how much insulation can I add before I get into trouble?’” says Lstiburek. “You’re going to hate this answer or love this answer — depending on whether you’re a client or a consultant. The consultant’s answer is, ‘It depends.’”

Clearly, fiberglass batts should never be used to insulate the interior of a brick wall. (Since fiberglass batts are permeable to vapor and air, they permit interior moisture to condense on the cold bricks. That's bad.) Most experts agree that the best insulation for the interior of an old brick building is closed-cell spray foam. In most cases, the foam is sprayed directly against the interior side of the brick. To determine how thick you can go, you’ll need to talk to your consultant. “We take samples of brick and send them to John Straube for the hot and cold soak test,” says Brennan. “Then he does WUFI modeling. We generally end up installing about 3 inches of closed-cell foam.”

It's possible to insulate the interior of an old brick wall with rigid foam; if you want to try this approach, a useful resource is a U.S. Department of Energy document, Installing Rigid Foam Insulation on the Interior of Existing Brick Walls. Even though this publication provides guidance on installing rigid foam, the authors note that "closed-cell polyurethane foam ... sprayed directly onto the brick masonry ... is the most effective, though costly, method for insulating the interior of brick walls."

If the building is vulnerable, don’t insulate the walls

In some cases, your consultant may advise you that it’s best to leave your walls uninsulated.

“Sometimes you just don’t insulate the walls,” says Straube. “Even if the walls are left uninsulated, you can often reduce heating demand by 50% by addressing air sealing, the basement, the roof, and the windows.”

Can I use cellulose?

Some energy experts have insulated old brick buildings on the interior with cellulose. One of the pioneers of this technique is Chris Benedict, a New York City architect.

Benedict described her technique in an article published in the March/April 2010 issue of Home Energy magazine. “In 1998 I started specifying a wall assembly for masonry buildings comprised of 2 5/8-inch metal studs at 16 inches on center, 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 5/8-inch gypsum board,” Benedict wrote. “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 insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection. was then blown into the 4-inch or 5-inch cavity at 3 1/2 lb. per cubic 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. … to date I have yet to see a masonry building destroyed by insulating it.”

Like other experts interviewed for this story, Benedict emphasizes water management. “As part of the scope of my work I make sure that the wall is pointed and in good repair,” she wrote. “The building is thoroughly assessed for any damage to bricks and mortar inside and out. … If a building is showing any problems with liquid water management, these problems must be resolved prior to insulating.”

I asked John Straube how he felt about Benedict’s technique. “I have qualms,” he told me. “But if the air sealing is done right, I don’t think there is a problem. First you have to walk around the building and see if it leaks. Then you ask, can I get it airtight? You need to install a fluid-applied membrane that is vapor-permeable but airtight on the interior surface of the bricks.”

Straube prefers closed-cell spray foam. “One thing about spray foam: it does a really good job or air-tightening, as well as some water tightening,” he says.

More maintenance

According to Bill Rose, a research architect at the Building Research Council at the University of Illinois, anyone who insulates the interior of an old brick building should plan to inspect the exterior on a regular schedule.

Rose imagined a conversation with a building owner. “People say, ‘We have a mandate to put insulation on our walls. How much damage will happen to this building if we insulate at the interior?’ I say, ‘If you do that, during winter the exterior materials will be wetter than they used to be.’ So then I’m asked, ‘What is the range of damage?’ And I say, ‘Everything falls into the maintenance range. You’ll need to increase the maintenance budget.’ There is uncertainty, but I’m happy to go forward if we include the concept of increased maintenance. That’s how we address worry problems. We have to have more eyes on what happens.”

Can I go forward without a consultant?

If you own a building with low risk factors, you may decide to go ahead without hiring a consultant.

An example of a building with low risk factors would be a building in Philadelphia with no signs of exterior water damage, without any deteriorating bricks, and with flashings that do a good job of keeping rainwater off the building.

Last week’s blog: “Utility-Scale Wind Turbines.”

Tags: , , ,

Image Credits:

  1. John Straube
  2. Terry Brennan
  3. Building Science Corporation

Aug 13, 2011 2:48 AM ET

Edited Aug 13, 2011 3:59 PM ET.

Foam Injection
by Kevin Dickson, MSME

Denver's most respected home energy upgrading contractor has been injecting foam into brick walls for years. In a double wythe wall, you can sneak in an inch of foam for an R value of 6+.

Dennis Brachfeld of AAS reports no moisture problems (Denver is relatively dry) and much increased comfort. It's a very expensive procedure, even without building a new interior wall, so they rarely do an entire home, just the most uncomforable rooms.

In my own testing, I found that the "blue can" Great Stuff (low expansion) fills the wythe cavity much better than the cheaper, standard "red can" stuff.

Note: foam injection may cause worse problems even than insulation on the inner wall. That's because it plugs the cavity behind the exterior bricks. This cavity is traditionally relied on to help drain and dry the brick. So stay away from this method if you have rain in the day with freezing at night.

Aug 13, 2011 3:34 PM ET

by james brown

"Clearly, fiberglass batts should never be used to insulate the interior of a brick wall."

is fiberglass so bad? Even when used with a good vapour check on the interior? It will allow the wall to dry to the inside, will closed-cell spray foam allow this?

Aug 13, 2011 4:30 PM ET

Response to James
by Martin Holladay

Q. "Is fiberglass so bad?"

A. Yes. It is almost impossible to make drywall so airtight that interior air will never contact the bricks and lead to condensation.

Q. "Even when used with a good vapour check on the interior?"

A. The problem has more to do with air leakage and air convection than vapor diffusion.

Q. "It will allow the wall to dry to the inside."

A. Precisely my point -- you don't want to allow vapor diffusion to occur between the warm, interior air and the cold bricks -- a vapor-open assembly is counterproductive.

Q. "Will closed-cell spray foam allow this?"

A. No, and that's a good thing.

Aug 13, 2011 5:26 PM ET

Edited Aug 13, 2011 5:28 PM ET.

fiberglass again
by james brown

I ask because you don't advocate interior polyethylene barriers because that stops the wall drying to the inside, but you are advocating closed-cell foam which will also stop the wall drying to the inside. Am I misunderstanding something? I don't want to install the wrong material in my renovation. No one over here (UK) uses spray foam on bricks, most use closed-cell foam boards.

Also perhaps cellulose has worked (as mentioned in the article) as it has vapour resistivity between mineral wool and closed cell foam. (I'm using figures for resitivity from the following document, pg 3 and 4). However, the cellulose manufacturer does not recommend cellulose on solid masonry walls.

By the way you might be interested in some of the projects on that site (eg the solar slab).

Aug 14, 2011 5:10 AM ET

Response to James Brown
by Martin Holladay

You're right -- I don't advise the use of interior poly in most climates. However, interior poly makes sense in much of Canada and Alaska -- at least on the interior of wood-framed buildings.

Load-bearing brick walls differ in many ways from wood-framed buildings, however, as I try to make clear in the article. I don't think you should use any rules of thumb from wood-framed construction when insulating an existing building with load-bearing brick walls. In case you are wondering, I don't advocate the use of interior poly when insulating brick walls.

Rigid foam boards can be used to insulate the interior of a brick wall, as long as the seams between the sheets are carefully sealed with caulk, canned foam, or tape. All of the other advice in the article above would still need to be followed: deal with the rain, assess the bricks, consider the climate, and don't install too much insulation.

Cellulose insulation differs in two important ways from fiberglass batts: dense-packed cellulose does a much better job of limiting air infiltration than batts, and cellulose is hygroscopic. If you were to use fiberglass batts to insulate a cold brick wall, condensation could run down the brick wall and pool on the floor. If you install cellulose -- still an experimental method, and probably risky in cold climates -- the cellulose is able to absorb and store a certain amount of moisture that might otherwise condense against the cold bricks. If the wall assembly allows drying to occur at a faster rate than moisture accumulation -- something that can be determined by WUFI -- such walls can succeed. Perhaps.

Aug 14, 2011 6:16 AM ET

Edited Aug 15, 2011 3:47 AM ET.

by james brown

thanks Martin. I've got a better grip on the issues now.

Aug 15, 2011 3:55 AM ET

by james brown

I know cellulose is best applied damp with a blower machine but these can't be rented in the UK. Is it feasible to mix the cellulose with say, a paddle mixer in a big bucket, adding water and then apply it by hand, a bit like rendering/harling/plastering? This would be for filling the gaps between studs before drywalling over.

Aug 15, 2011 4:35 AM ET

Edited Aug 16, 2011 3:32 AM ET.

Response to James Brown
by Martin Holladay

I don't recommend your suggested technique, for a variety of reasons. The technique introduces too much water; you won't be able to fill all the gaps; and the density of the installed insulation will be too low.

Insulating the interior of a brick wall is tricky. You want a carefully air-sealed assembly. If you want to insulate with cellulose -- I method I don't recommend -- then I suggest you take John Straube's advice: "You need to install a fluid-applied membrane that is vapor-permeable but airtight on the interior surface of the bricks." This is not a method that is appropriate for do-it-yourselfers who spread gobs of insulation with their hands.

My advice is to hire an insulation contractor experienced at insulating brick walls.

Aug 15, 2011 3:29 PM ET

Extending existing buildings
by Buildingwell .org

This article brings up a number of good points about insulating brick buildings to help extend their lifetimes. While it's true that the preferred method would be to insulate the exterior, there are a number of reasons that may be impossible - many times related to historic reasons such as for credit, zoning or funding. Insulating the interior as you've stated really comes down to "it depends" which is probably the best way to put it. A professional can be most helpful in determine whether the interior insulation is really the best thing for the brick building and if so, to what extent. In the end, the deciding factor should be the cost and life-cycle assessment for your options.

Aug 15, 2011 3:53 PM ET

insulating brick house from outside with foam
by Robert Haverlock

As I understand it, your saying insulate from the inside, but not outside. I witnessed a foam company insulate from the outside by drilling holes in the gaps 16in on center, Does this, or could this not also fill up any rain plaine designed into the home? And I have not read in this blog anything about rain plaines being involved? Here in Seattle Washington.

Aug 15, 2011 4:00 PM ET

Edited Aug 15, 2011 4:01 PM ET.

Reply to Robert Haverlock
by Martin Holladay

All of the information in this article is about multi-wythe load-bearing brick walls. Such walls were commonly built in decades past; most such buildings in the U.S. are between 90 and 200 years old.

Your comment mentioned "rain planes." I assume that you are referring to the drainage gap in a brick veneer wall. Brick veneer walls are built completely differently from mult-wythe load-bearing walls. The typical brick veneer wall is non-structural. A single wythe of bricks is installed; between the brick veneer and the wall sheathing is a drainage gap that shouldn't be blocked or filled. Most brick veneer buidlings are actually wood-frame buildings; the wood-frame wall is the load-bearing wall.

If any insulation contractors are installing spray foam in the drainage gap of brick-veneer walls, they are making a mistake. These drainage gaps should not be filled.

Aug 15, 2011 5:56 PM ET

Edited Aug 15, 2011 6:03 PM ET.

by james brown

"you won't be able to fill all the gaps; and the density of the installed insulation will be too low"

It seems unlikely to me that the machine could apply the cellulose with more force than I could apply by pushing it on with a hawk and trowel (or similar, eg tamping it. Or, as you say, literally with your hands!) This is for a situation where you have yet to sheet over the stud walls. I'm not suggesting it would be possible to fill a cavity via holes by hand successfully.

"My advice is to hire an insulation contractor experienced at insulating brick walls"

Over here that would result in laminate foam board, or foam board in stud bays then drywalled over. This method has too many detailing requirements to leave to a contractor. I think the spray method ('liquid applied' as you referred to it) is great as it as it would ensure a full fill. My main reluctance to use sprayfoam is the risk it poses to joists / timbers embedded in the masonry. I feel cellulose may buffer the humidity and help move water away from the structural timbers to avoid them rotting.

Aug 17, 2011 5:22 PM ET

Good Read
by Eric Novotny

Very good read and even. We don't have to worry about many of these issues in my climate region but I thought the article, and follow up, was well done.

Aug 17, 2011 5:31 PM ET

Silane Water Repellent?
by Eric Dymond

Couldn't you minimize the amount of moisture penetration by using a silane/siloxane water repellent? That would allow the brick to dry to the exterior while preventing moisture intrusion.

Aug 17, 2011 11:49 PM ET

Insulating between the wythes
by Jim Baerg

Hello, very timely subject for me. I've got a double whythe, load bearing house and would like to place insulation between the whythes in the 2.5-3 inch gap. Preserve the exterior and avoid a complete interior remodeling job are the reasons. Plus fantastic thermal behavior in the summer with the added mass.
Location is dry and cold, 12 inches of precip/year, half in snow. 8000HDD. Absolutely no sign of moisture related deterioration anywhere in the house. The roof is steep and has gutters but the bricks are pretty soft. Interior is plaster directly on the brickj and the basement is dry.
So, I've looked at UF, Air Crete and low rise 2 part foam primarily because they can be injected in the mortar joints. Part of the difficulty is finding an applicater.
What would you recommend in terms of insulating the void? Can it be done safely and what type of insulation would you recommend.
Attached is a photo.
Thanks, Jim Baerg


Aug 18, 2011 4:34 AM ET

Response to Eric Dymond
by Martin Holladay

In general, historic preservationists and most building scientists agree that, although silane/siloxane coatings may have their applications for specific problems, they should not be used as a general solution to try to improve the hygrothermal performance of all of the walls of an existing building. Their performance and longevity are questionable.

Aug 18, 2011 4:35 AM ET

Edited Aug 18, 2011 4:36 AM ET.

Response to Jim Baerg
by Martin Holladay

My advice to you is the same as the advice presented in the article: hire a consultant experienced in these issues, and have your bricks tested. (Although if you are unable to locate a contractor willing to do the work you propose, the entire issue may be moot.)

Aug 20, 2011 12:32 PM ET

Lime wash as water repellent?
by Marcus de la fleur

Eric asked above about silane/siloxane water repellent. While discussing this topic with a restoration mason, he mentioned lime wash, which is apparently suitable for old(er) load bearing masonry walls. Each lime wash application lasts only for a few years, but it is said to improve the hygrothermal performance of the wall. Any opinion on this option?

Mar 5, 2012 9:44 PM ET

Internal Insulation of Masonry Walls Measure Guideline
by Kohta Ueno

If anyone is interested in BSC's current document on the subject, our Building America-sponsored research report has recently been finalized:

RR-1105: Internal Insulation of Masonry Walls: Final Measure Guideline

Mar 6, 2012 5:34 AM ET

Response to Kohta Ueno
by Martin Holladay

Thanks, Kohta. I've added a link to the document in the "More Information" sidebar.

May 23, 2012 3:52 PM ET

I know this article is a bit
by Randy Starr

I know this article is a bit old, but are these concerns basically limited to cold climates? I am down in New Orleans where it only freezes occasionally in the winter but we do have a ton of moisture (both bulk and vapor). Is this freeze/thaw concern really only a problem in the North with repeated and extended freezing / thawing cycles?

May 23, 2012 4:15 PM ET

Response to Randy Starr
by Martin Holladay

Yes, these concerns are limited to cold climates. As building scientist Joe Lstiburek, who was quoted in the article, said, “It’s rare that we have to worry about freeze/thaw problems in places like New Jersey and New York City.”

None of the concerns mentioned in this article apply to buildings in New Orleans.

May 23, 2012 4:32 PM ET

Awesome. Thanks.
by Randy Starr

Awesome. Thanks.

Aug 14, 2012 8:38 AM ET

by Matthew Emerson

Thank you for writing this article. My wife and I are currently looking to relocate to another home in Philadelphia, which of course, means old double-wythe construction! As we look I'll pay closer attention to the brick conditions on the exterior, particularly around chimneys and parapets. I found it interesting that you referenced Philadelphia as an area that wouldn't be a problem to insulate from the interior. I would still be a little wary of adding too much insulation, as there can be prolonged periods of wet winter weather, especially the last few years. Additionally, I disagree with the EIFS recommendation, as I believe it's an inferior product as well as a dangerous one. Here in Philadelphia there are a lot of contractors installing it, only to have it redone shortly after. Many times, it's the installation and flashing detailing, etc. I will personally be looking into mineral wool open joint rainscreen on the rear / side where the street presence isn't as important to the block conformity.

Any articles on insulating attic spaces? I know there are a lot of flat-roofed homes in the Northeast that are un-insulated in the tight void space between the roof and ceiling.

Aug 14, 2012 9:13 AM ET

Response to Matthew Emerson
by Martin Holladay

The best way to insulate a flat or low-slope roof is with a layer of rigid foam above the roof sheathing. That means that insulation upgrades are usually performed when it is time to install new roofing.

Oct 25, 2012 4:32 PM ET

Following the question about a flat roof.
by Eddy Trochez

Will Roxul and a vapor barrier be a good solution for a flat roof (NYC area)? Will this method cause problems with the embedded wood joists in a load-bearing brick wall? I will not insulate the walls, only the ceiling and overlap the vapor barrier a few inches with the wall. Thanks in advance.


Oct 25, 2012 8:21 PM ET

Response to Eddy Trochez
by Martin Holladay

In the response posted on this page immediately above your question, I wrote, "The best way to insulate a flat or low-slope roof is with a layer of rigid foam above the roof sheathing."

If you want to insulate below the sheathing, I recommend that you use closed-cell spray foam.

Roxul is a bad choice because it is air-permeable. It can allow warm, moist interior air to reach the cold roof sheathing, leading to condensation.

A polyethylene vapor barrier is not recommended for this application. It will not prevent air movement from the interior to the sheathing. It's impossible to install poly in a way that is totally airtight -- and in any case the trapped air would inevitably have moisture in it anyway.

Nov 7, 2012 6:34 PM ET

Thanks Martin for the help.
by Eddy Trochez

Thanks Martin for the help. Some people are installing rigid foam bellow the sheeting and sealing the edges with foam or caulk. How do you feel about this approach?

Nov 8, 2012 8:53 AM ET

Second response to Eddy Trochez
by Martin Holladay

That approach -- sometimes called "cut and cobble" -- can work, but it has two disadvantages:

1. Obtaining an airtight installation (which is essential) is fussy, time-consuming work.

2. Even if the work is perfect, you still have thermal bridging through the rafters.

Nov 8, 2012 1:03 PM ET

Edited Nov 8, 2012 1:05 PM ET.

Thanks Martin
by Eddy Trochez

I was doing some reading (your article here on GBA) regarding the possible health issues with spray foam. The situation definitely makes it more difficult for the DIYer, and the cost to hire a professional is sometimes astronomical for this type of job. What kind of advice would you give to somebody who wants to do it himself? Is it worth it? I'm convinced that spray foam is the way to go in my situation, but the thought of having lingering fumes and smells is very scary.

Nov 8, 2012 1:26 PM ET

Third response to Eddy Trochez
by Martin Holladay

Only you can make that decision. You have to weigh your expected energy savings against the expected cost of the work, and decide whether you feel comfortable using spray foam. It doesn't matter what I think -- only what you think.

The best approach is to combine new rigid foam on top of the roof sheathing with a re-roofing job.

Nov 8, 2012 3:16 PM ET

Edited Nov 8, 2012 3:17 PM ET.

Thanks Martin
by Eddy Trochez

If it wasn't for this site, I would've made a big mistake. Local contractors wanted to blow in insulation.

Question regarding the rigid foam.
Will I need a second layer of sheathing on top of the rigid foam? Can you point me to a good online resource on the subject?

Thanks a million,

Nov 8, 2012 3:28 PM ET

Fourth response to Eddy
by Martin Holladay

No, you don't need any sheathing on top of the insulation. Here are two articles to help you:

How to Insulate a Low-Slope Roof

The Rundown on Low-Slope Roofing

Jun 9, 2013 8:45 PM ET

by Joanne Alfonsi

If old brick walls are patched and repointed with cement based mortar they spall. Spray foam insulation becomes extremely hard and impermeable (like a cement based mortar). if the spray foam is applied to the interior would it not cause the same spalling problem on the interior of the wall. would it be better to apply a rigid foam insulation board and then an inch of spray foam. Would you for see any problems with this method? I would be reluctant to spray directly onto the brick. This would be an R value of 12 or so. We are based in Toronto and our bricks appear in great condition (even in the chimney)

Jun 10, 2013 5:59 AM ET

Response to Joanne Alfonsi
by Martin Holladay

The problem you describe -- repointing an older brick building (most of which have lime-based mortar) with Portland-cement-based mortar -- is independent of the problem described in this article (insulating an older multiwythe brick wall on the interior). Obviously, there is more than one way to damage an older brick building. Choosing the wrong repointing mortar is one way to damage it. Insulating it incorrectly is another way.

I stand by the advice given in this article. If you want to insulate a brick wall on the interior, follow all the steps listed in this article before you proceed. If you are sure that it is safe to proceed, then closed-cell spray polyurethane foam (sprayed directly on the interior of the bricks) makes more sense than rigid foam.

Jun 18, 2013 8:01 AM ET

Philly Double Wythe Detail
by S. Tunji Turner

Hey all, just finalizing on a wall detail for my breezeway double wythe brick wall. I would add 2" polyiso foam board with reflective side showing, with a open joint rain screen system ( Hardie Panel,etc). My inside was my greatest concern. I have decided to frame 1.5" away from the interior brick, with 1 " spray foam sprayed directly on the brick, and then denim insulation in the 2x4 cavity 16"oc. And 3 mil plastic sheathing before 1/2" sheetrock. Any suggestions/advice would be appreciated, thx

Jun 18, 2013 8:18 AM ET

Response to S. Tunji Turner
by Martin Holladay

S. Tunji Turner,
My advice hasn't changed since I wrote the article. So: if you are leaving the exterior bricks exposed, the only insulation to consider is closed-cell spray polyurethane foam. And that should only be used if you feel confident about your exterior water management details and the quality of your bricks.

If you are willing to cover up the exterior bricks -- and it sounds like you are -- I would put all of the insulation on the exterior of the building. Two inches of polyiso is better than nothing, but I would aim for at least 4 inches of polyiso if I were you.

Jun 18, 2013 6:15 PM ET

Response to martin
by S. Tunji Turner

So you are suggesting 4" exterior with a rain screen , soffit box, water management. and then no foam on inside, just the denim insulation on the inside w/plastic.

Jun 18, 2013 8:25 PM ET

Response to S. Tunji Turner
by Martin Holladay

S. Tunji,
No denim insulation. No interior polyethylene. Otherwise, you've got it.

Aug 11, 2013 12:03 AM ET

Brick walls in Arizona
by anita b

Hi- I hope this blog is still active.
We live in a 1961 brick house in Tucson, AZ, without any insulation of the exterior brick walls. Brick is about 4-inch thick (yes, we basically live in a brick oven). We would like to insulate inside. I don't think we have to worry about the freeze/thaw problems, but not sure what materials do use. Some folks here that have experience say, fiberglass batts are just fine and less expensive. We also looked at the rigid foam-sheets.
Any advice?

Aug 12, 2013 10:11 AM ET

Edited Aug 12, 2013 10:14 AM ET.

Response to Anita B.
by Martin Holladay

In your climate, you can insulate the interior of your walls without worrying about freeze/thaw damage.

I don't recommend that you install fiberglass batts, for two reasons: (1) Fiberglass batts perform worse than all other insulation types, and (2) If they were insulated with fiberglass batts, your walls would be susceptible to inward solar vapor drive problems, especially if your house has air conditioning. (For more information on inward solar vapor drive, see When Sunshine Drives Moisture Into Walls.)

I advise you to install rigid foam insulation on the interior of your walls. Polyisocyanurate insulation is the most environmentally friendly type of rigid foam insulation, and it has the highest R-value per inch. Polyiso performs well, and it will prevent any problems from inward solar vapor drive.

Aug 13, 2013 6:16 PM ET

by Jeff Speirs

Excellent article!
I have an 180 yr old house with load bearing brick walls in the Philadelphia area. The bricks have an exterior layer of stucco which has been painted. The house roof has a 2 1/2' overhang which keeps the walls fairly dry. The foundation is also brick and this allows some moisture to wick up into the above grade brick. The interior plaster is applied to lath on top of 1" thick furring strips. the gap created by the furring stips is open from the basement to the attic. Would it be advisable to insulate and/or seal the top and bottom of this 1" gap? If so, would vermiculite be an option? It seems like the easiest material to flow down into that narrow space.

Aug 14, 2013 5:52 AM ET

Response to Jeff Spiers
by Martin Holladay

While some people have used vermiculite to insulate the type of gap you describe, I don't recommend the practice.

The main problem with vermiculite is that it does little to stop air flow. If your gap is open from the basement to the attic, the most critical step for you to perform is air sealing. Every single channel needs to be carefully sealed in the basement as well as the attic. Unless you are planning to demolish your interior plaster, this work will need to be performed in the basement and attic, using a two-component spray foam kit.

One inch of air-permeable vermiculite wouldn't provide much R-value anyway.

Since the exterior of your building has been stuccoed, the best way to insulate the building is with an exterior layer of rigid foam. The most economical way to do this would be to finish the exterior with EIFS (rigid foam plus synthetic stucco). If you call up a few local EIFS contractors, you should be able to get bids for the work.

If you prefer to do the work from the interior, I recommend that you follow the advice in the article, by installing spray polyurethane foam against the interior of your brick walls. That will require you to demolish the interior plaster.

Oct 20, 2013 10:29 AM ET

Edited Oct 20, 2013 2:53 PM ET.

Freeze/thaw concerns in DC?
by Diane McAvoy

The article and commentary have been so helpful for my current predicament. I bought a 100yr. old double wythe end-unit row house about four years ago that had been flipped. This past spring the house started to feel very humid. I started to notice mold in my closet (on an 2nd floor exterior, northern wall). After several consultations with an industrial hygienist, we started to discover more mold on the western and northern walls where the air was stagnate (behind pictures, closets, etc). We determined that the mold was caused by a vapor drive issue from the exterior brick. It was getting caught in middle of the wall and then condensing in the cooler months, not drying, and then providing the conditions for mold to grow inside the wall the spring/summer. The mold I saw behind my pictures was because the drywall was saturated with water. When they flipped the house, they applied drywall directly to the old plaster without a vapor barrier. In some cases there was also wallpaper attached to the plaster and then drywall over it....a recipe for disaster that I am now living out.

I have performed the mold remediation steps and am now left with very old plaster and in some areas just brick where the plaster has fallen off. My next task is to figure out how to rebuild in a manner that will prevent vapor drive to the inside AND reduce the risk of condensation inside the wall structure. While I've consulted with several structural engineers and performed lots of internet research (love building science articles), I'm still not confident of the best way to address the issue without causing unintended consequences.

The first step I am taking is to remove the remaining plaster and repoint the interior brick with Type N lime mortar and then apply a brick sealer on the interior. My current plan to finish the wall is to frame out the inside using 1.5" x 3.5" studs, leaving about an inch gap between the frame and the brick and the framing oriented like in the picture below (my current kitchen). From there, I wanted to hire a spray foam contractor to apply 2" of closed-cell spray foam insulation that would fill in the 1" gap behind the framing plus about an inch into the frame cavity. After that, I would reapply drywall. I think this would address both my vapor barrier and condensation concerns, but I am not sure how it would address the freeze/thaw concerns. I read it is not a concern in NYC, so I assume DC is fine to use this method. Do you see any red flags with my approach? This is not my area of expertise and I've found that different people have lots of different opinions. This is all really expensive and unexpected, so I only want to do this once, so am just looking for some validation that I am on the right track. Thank you so much!

Diane in DC


Oct 21, 2013 6:52 AM ET

Edited Oct 21, 2013 6:58 AM ET.

Response to Diane McAvoy
by Martin Holladay

Your case raises many questions.

First of all, the climate in your location (Washington, DC) is mild enough that you really don't have to worry about freeze/thaw damage to your bricks. In general, it should be safe to insulate the interior of your walls with closed-cell spray polyurethane foam.

But your mold situation is unusual, and the actual mechanism is a little puzzling. I suspect that two factors may be at work here: the exterior of your bricks may be unusually wet -- which would be the case if your house had insufficient roof overhangs or some type of flashing problem -- and (perhaps) the interior finishes on the walls were vapor-impermeable. (The classic problem occurs with vinyl wallpaper, which is a disaster if used in an air-conditioned home in a humid climate.)

In your climate, an uninsulated brick wall doesn't usually grow mold. During the winter, the indoor air is usually dry, and the bricks are kept warm by your heating system. During the summer, if the house is air conditioned, the indoor air is dry, and any moisture in the bricks dries inward -- unless, of course, there is vinyl wallpaper to mess things up.

Without a site visit, I can't know what's going on at your house, of course, and you shouldn't take any action based on my speculation.

You shouldn't proceed with a remedy, in my opinion, until you fully understand the mechanism that created the mold. It's possible, for example, that your house has a wet basement or a wet crawlspace, and that the mold grew during the winter; this might have happened if all of the rooms of your house weren't heated.

Any remedies have to start with the basics. You need to do everything you can to keep rain off of your bricks, and that might require better roof overhangs. And you need to be sure that you don't have a wet foundation.

Oct 21, 2013 10:22 PM ET

by Diane McAvoy

Thank you for your comments, Martin. I will look into other factors that may have contributed to moisture accumulation in the wall besides just vapor drive-related moisture getting stuck and condensing in between the plaster and paper-backed drywall. I'll keep you posted. Best, Diane

Oct 22, 2013 6:08 AM ET

Response to Diane McAvoy
by Martin Holladay

It's impossible for moisture to "get stuck and condense between plaster and paper-backed drywall." Paper-backed drywall is hygroscopic and vapor-permeable. When it gets wet, it dries rapidly to the interior of the house -- unless someone installed vinyl wallpaper, or unless someone glued a mirror to it.

Oct 22, 2013 10:40 PM ET

We recently purchased a 2.5
by Colin Marshall

We recently purchased a 2.5 story brick masonry home in Chicago that we plan to renovate. Upon demolition of the kitchen, I discovered moldy batt insulation between a plastic sheathing (the last renovator's vapor barrier form 1983?) After reading your article, and the ones on BSC this made sense. I raised the issue with my architect and asked how we should address and this was his response...

"We have typically installed a vapor barrier on the inside face of the masonry wall with 2" rigid foam insulation between wood or metal studs, and then we use a secondary vapor barrier on the inside face of the studs (between the studs and the gypsum board). Properly installed, this isolates the insulation and framing from condensation or water infiltration from either side of the interior wall assembly. Rigid foam is considerably more expensive than batt insulation (when calculated as dollars per R-Value) but I will investigate the cost of spray on insulation (I have pricing estimates from another project that I can reference). My concern is that spray on insulation will prevent the masonry wall from properly breathing thus trapping moisture in the wall and causing efflorescence and deterioration of the masonry."

1) Can you recommend any consultants in Chicago?
2) Is it time for a new architect?

Oct 23, 2013 4:47 AM ET

Response to Colin Marshall
by Martin Holladay

Sandwiching insulation and studs between polyethylene doesn't work, because it's impossible to make the poly layers completely airtight, especially on a job site. (Even in a university lab, it would be a difficult challenge.) Changes in temperature and air pressure will cause a pumping action that leads to air exchange between the air trapped between the polyethylene layers and the air on the exterior or interior side of the sandwich assembly. When humid air enters the sandwich assembly, it can trap moisture between the poly layers. Later, when one side of the poly sandwich gets cold, water will condense on the poly and run down to the bottom of the sandwich, and will pool at the bottom plate.

Spray polyurethane foam insulation is the recommended insulation material to use on the interior of a multi-wythe brick wall -- subject to the caveats listed in this article.

The sentence, "My concern is that spray on insulation will prevent the masonry wall from properly breathing thus trapping moisture in the wall and causing efflorescence and deterioration of the masonry" doesn't make any sense. If the architect wants the brick wall to "breathe" to the interior, why is he suggesting the installation of polyethylene -- a layer that limits "breathing"? Clearly, a multi-wythe brick wall that is insulated on the interior will "breathe" (I would say, will dry) to the exterior, not the interior. There are still risks, of course, especially in freezing climates. These risks are explained in the article.

If you want to hire a consultant, the consultant doesn't have to live in Chicago. It's hard to beat the consultants at the Building Science Corporation in Somerville, Mass., or at Building Science Consulting in Waterloo, Ontario.

Only you can decide whether it's time for a new architect. It sounds like your current architect will need a little hand-holding or guidance because of an incomplete knowledge of building science. Unfortunately, that's not unusual -- so switching architects may not help.

Dec 3, 2013 3:07 PM ET

mortar and paint
by Owen Sechrist

In my local many of the buildings are over 100 years old and were constructed with a very soft brick and limestone mortar with no portland cement. My understanding is that because the combination of soft brick and self-healing mortar allows for resiliency in freeze-thaw cycles.

When I observe buildings with damage to the brick it is often caused by either direct water/drainage issues or re-pointing with hard portland based mortars.

Is soft brick and limestone mortar more resilient to being insulated on the interior?

How does exterior painting affect the insulation scenario?

Register for a free account and join the conversation

Get a free account and join the conversation!
Become a GBA PRO!