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Community and Q&A

Insulation of old brick exterior walls

mqTtQVWZPv | Posted in Energy Efficiency and Durability on

I have reviewed the blogs regarding insulation of old brick exterior walls and am confused. There is significant rain damage on the bricks which are now repointed. There is a gap between the studs (2X4 on 24 inch centres – real 2×4). There was once tar paper attached to the exterior studs. Someone insulated it with pink batts at one time- which has been removed.

I live in Southwestern Ontario where it gets cold in winter with high humidity/heat in the summer. The existing studs are significantly rotted and need to be replaced. Should I replace the studs with real 2×4’s on 24 centres? Would the addition of metal studs – from the wood to the brick- help conduct heat to help the bricks stay warm and dry? Is the layer of tar paper beneficial to the protection of the insulation? (I understand the bricks are already an air barrier, now they are repointed).

I will deal with the water issue when I install the roof, with flashing and proper drainage flows. I already dug away from the foundation and shored it up with steel I-beam, that exends 2 1/2 feet past the edge, held in place by anchor bolts and steel posts filled with concrete.

I do not have much $$ and have been doing this myself with my children, so I need to do it right the first time. I found a local wood mill that will cut the 2×4’s but I am concerned about rot with the condensation created by heating/cooling bricks. I do not want to cover the bricks on the outside, nor coat them in something that doesn’t allow them to breathe naturally. There is an uninsulated crawl-space with a dirt floor beneath (which I will insulate) and it is vented with grates built into the foundation.

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  1. GBA Editor
    Martin Holladay | | #1

    Do you know whether your 2x4s are load-bearing? If you have only one wythe of bricks, they probably are. In that case, you have a wood-framed house with brick veneer.

    If you have several wythes of bricks, then it's probable that your brick wall is structural and load-bearing.

    It's important to be clear which type of house we are talking about before anyone can give you advice.

    By the way, a brick wall is not an air barrier. Brick walls leak air.

  2. mqTtQVWZPv | | #2

    It is a load bearing wall

  3. GBA Editor
    Martin Holladay | | #3

    1. The first step is to determine why the 2x4s rotted and to remedy the moisture problem that led to the rot. I have no idea why they rotted.

    2. You asked, "Would the addition of metal studs - from the wood to the brick - help conduct heat to help the bricks stay warm and dry?" Maybe, but if you try to keep the bricks warm and dry by conducting interior heat in that direction, you will go broke. I don't advise any scheme to increase heat flow from your house to the bricks.

    3. I assume you read this article: Insulating Old Brick Buildings.

    4. Once you have solved your moisture problems, improved your flashing, repaired your roof, and figured out why your 2x4s are rotten, you can consider installing insulation. The standard insulation is closed-cell spray polyurethane foam -- but not too much. My article (see link above) explains why there is no simple way to make recommendations about such buildings without a site visit.

  4. mqTtQVWZPv | | #4

    Thanks Martin

    I am at the point where I need to buy the studs and do not have money to have foam insulation. Thus, I am considering the ‘less is more’ advice of the Insulating Old Brick Buildings article. I was originally going to put 2x6’s with high R rating (which needs more depth), however this would definitely freeze the bricks, causing more damage.

    I can’t repair the roof until I restud the walls. You wondered about the rot…. Years of water channelled though a downspout that ran into the foundation of the addition (a trapezoid shape). The addition started to sink along the front, creating a gap at the roof line. Water then ran through the roof along the vapour barrier and down into the walls, rotting the studs in the roof and the walls. Hence, the need to refortify the foundation to prevent further movement.

    This brings me to the insulation question, so I can plan the studs. My understanding is that there is going to be some heat loss along the studs, however minimal. I thought perhaps that if I used this heat loss (conducted by bridges of metal studs touching the bricks), to warm the bricks, I could use a higher R rating of insulation, without increasing the risk of freezing the bricks. You have advised this is not wise. Thus, less insulation in 2x4’s will be needed, leaving me with the question of where to install the vapour/air barrier … tar paper between the bricks and the studs, or plastic between the studs and the drywall, or just seal, tape and paint the drywall? Or a combination thereof.

  5. GBA Editor
    Martin Holladay | | #5

    My advice was to hold off on insulation until the roof was repaired and the rotten 2x4s are replaced. Then, and only then, you could consider installing closed-cell spray foam.

    You wrote, "I was originally going to put 2x6’s with high R rating (which needs more depth), however this would definitely freeze the bricks, causing more damage ... I thought perhaps that if I used this heat loss (conducted by bridges of metal studs touching the bricks), to warm the bricks, I could use a higher R rating of insulation, without increasing the risk of freezing the bricks."

    It sounds to me like you are planning to install some type of insulation. What type of insulation are you planning to use?

  6. mqTtQVWZPv | | #6

    Pink fiberglass - R14 if 2x4's are used and R20 if 2x6's are used. What size studs(and insulation) will best protect the brick given my budget? What vapor barrier is best?

  7. GBA Editor
    Martin Holladay | | #7

    Fiberglass batts cannot be used to insulate the interior of a multi-wythe brick wall, as I explained in my article. The problem is that the insulation is air-permeable.

    If you are able to install a layer of asphalt felt between the bricks and your interior stud wall, that would be better than using polyethylene. I don't recommend the use of polyethylene or fiberglass batts. However, installing asphalt felt between the bricks and the studs will be tricky or impossible.

  8. mqTtQVWZPv | | #8

    Thanks again!! Since I have to replace all the inside studs I will put in a layer of ashphalt felt paper against the bricks. Spray foam is $2/ square foot as opposed to batts at $0.34/ sq ft. I could have fiberglass blown in at $0.45 sq ft, but I would have to put a vapor barrier between the studs and the drywall (blown in before drywall is attached) or just hang the drywall and drill holes through to blow it in.

  9. GBA Editor
    Martin Holladay | | #9

    I think I have given you good advice. I wouldn't use fiberglass batts if I were you. They are not appropriate for your type of wall.

  10. user-659915 | | #10

    Jacqueline, it seems you plan to install insulation to keep heat IN your building and at the same time to create deliberate thermal bridges to ensure heat leaks OUT of the building. Am I alone in finding this a confusing strategy, akin to calling for help, but not too loud to avoid disturbing anyone? If your goal is to warm the brick enough to mitigate frost damage, you could just use less insulation.
    Of course this approach has hardly been successful in the past - with little or no insulation your wall has already sustained damage. It's been a while since I've had to deal with freeze/thaw issues but if I'm not mistaken cold temperatures are only a problem for brick if it's saturated. Proper exterior water management with careful attention to overhangs, gutters and pointing (which you seem to already have in hand) should be the key to preventing further damage to the masonry. So now concentrate on making your insulation actually do its job and steer clear of thermal bridging as much as possible.
    Of course there should be an air gap, at least an inch and preferably two, between the brick and the insulated wood framing, with minimal structural connection between the two. Any wood directly in contact with the brick needs to be pressure treated.

  11. mqTtQVWZPv | | #11

    There is a gap there already that I can replicate. I have ordered the wood - at an amazing price - which could allow for spray foam insulation, but how do you recommend keeping it from filling in the gap between the wood and the brick - or is that preferable?

  12. GBA Editor
    Martin Holladay | | #12

    Once again, I urge you to read the article I linked to.

    When closed-cell foam is installed in an existing brick building, it is sprayed directly against the bricks. As I pointed out in the article, this is probably the best way to insulate -- but it may still be risky in some buildings. You need to consider your climate, your water-management details, and the quality of your bricks before proceeding.

  13. GBA Editor
    Martin Holladay | | #13

    Again, Jacqueline, I suggest you re-read the article. There is no simple answer to your question. It depends on your climate, the type of bricks in your wall, and the exposure to wind-driven rain, among other factors.

    As I wrote in that article:

    “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.”

  14. mqTtQVWZPv | | #14

    I have re-read and thinner sounds better to allow for some heat to escape to keep the bricks dry. The spay goes directly onto the bricks. If this was a wood frame new building, how thick would I want it sprayed on? Then I will ask for 1/4 of that, aiming for R 10-12.

    You realize that you are advising me to fill the 'rain plain' with insulation... you advise against this in other places, creating some confusion that I am hopeful you can clarify,

    You guys are awesome and I am glad I found you at the beginning of the week to allow for this communication. I apprectate your support and encouragement. Thanks!

  15. mqTtQVWZPv | | #15

    Martin - I was editing my question while you were answering... what about the 'rain plain'... spraying insulation on the bricks will close this gap

  16. GBA Editor
    Martin Holladay | | #16

    If you have a wood-framed house with brick veneer, an air gap between the bricks and the wall sheathing is essential. However, multi-wythe load-bearing brick walls are different; instead of managing water by drainage, they manage water by storing the water in the wall until it can evaporate. That's why it can be tricky to insulate an existing multi-wythe brick wall.

  17. mqTtQVWZPv | | #17

    The stud wall is load bearing. The brick wall is about 1 1/2 inches attached by metal rods from the wood to the bricks. The roof rests on the stud wall, not the bricks. Yes, it is tricky and I am having difficulty picturing how to spray in foam without filling the gap or using plastic. Will felt paper, applied to the studs (towards the bricks) hold the insulation over the long term or will it simply break down and allow the insulation to fall out of place? This brings me back to the beginning

  18. GBA Editor
    Martin Holladay | | #18

    In an answer to a previous question, you wrote, "It is a load-bearing wall," and I assumed you were referring to the brick wall (the title of your original question). Now you make it clear that the 2x4s are load-bearing, not the brick wall.

    If you have a load bearing 2x4 wall, and if your 2x4s are rotten, you need more advice than can be provided over the Internet. You need an engineer, and it may be necessary to completely remove the brick veneer wall to adequately address all of the problems your house is suffering.

  19. mqTtQVWZPv | | #19

    What if I framed the cavity of the studs with moulding strips and inserted foam board insulation, then used spray foam (in a can) to seal around the interior edges of the foam boards. This would insulate the stud wall and leave the gap between the bricks and the stud wall open, and the insulation won't slip out of place. I think the solution has to be creative to address all the difficulties of insulating the old brick wall, keeping it air/vapour tight, leaving the 'rain plain' and of course, keeping the room warm.

  20. mqTtQVWZPv | | #20

    We are on our way - builder with 60 years experience advised me to use the foam insulation board and tape the edges. My son cut 300 metal brackets to attach the studs to the bricks and maintain an even gap between them for the rain plane.

  21. mqTtQVWZPv | | #21

    My son cut 300 L-shaped metal brackets to attach the old brick to the new studs. We maintained the 'rain-plane' and applied the felt paper to the brick side of the stud walls prior to lifting them in place. Once the roof is shingled and gutters are in place, we will work on the insulation with foam boards and seal the edges. It smells of wood (instead of mold) and I am so proud of the kids for their hard work. They are learning alot too.

  22. homedesign | | #22

    I can't imagine how you are doing this with the brick veneer still in place...
    How about posting some photos?

  23. user-651098 | | #23

    Your metal L brackets will be thermal bridges between the studs and the brick. You could get condensation forming on the metal and promote rot in the studs.
    At the bottom of the brick veneer wall, ensure that you have weeps which allow any moisture to escape.
    This retrofit, on a limited budget, sounds like a complicated and quite technical challenge. Good luck.

  24. GBA Editor
    Martin Holladay | | #24

    Jacqueline has had plenty of warnings, but is proceeding regardless.

  25. mqTtQVWZPv | | #25

    I knee braced the back wall and removed most of the studs, leaving a couple of vertical studs attached to give it support. and off-set these from the new wall, which was built to lift in place. The old studs were attached by metal rods inbedded in the bricks. We cut these out with a saws-all. I know the metal will conduct some heat to the bricks, so we used as few as possilble to support the wall - I don't think we used more than 50. Big sheets of plywood up on the roof studs today; tomorrow cutting the fittings.

    I have to cut a chase in the bricks at the roof line for flashing. Originally it would have had lead flashing, which is thicker, but I will use the same technique to seal it. Most of the water problems originated from poor water shed, with two shoping roofs draining onto the addition we are reconstructing. I will channel these roofs directly to the ground and away from the foundation.

    I didn't take pictures to share, I will see if I can take some tomorrow. I was too busy working. I did not have money for hiring an engineer, which is why all the advice is appreciated. The studs rotted because water was streaming down the vapour barrier in the roof, directly down into the walls- literally - While this may not be a 100% better, it has to be 90%; good for another 100 years.

    Thanks for all your support and advice

  26. mqTtQVWZPv | | #26

    Still no time to take pics - roof is on- started insulation tonight.

  27. jmraine | | #27

    Question: I have a house built in the mid 60s . I just cut open the back split walls and found the lack of insulation in our brick exterior walls. There were days when the room was freezing so I want to add some insulation without hurting the bricks. Currently the layers from out to in are bricks -- building felt- 1" furring - 5 ply paper-wood "stuff"- 1" furring. The furrings are 18" apart. Should I remove the everything to the bare brick, redo furrings and use the 2" foam insulation for R-10 or do I have to leave space for air? Or can I just use our existing furrings and cut the 5-ply stuff out? Thanks for your help.

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