Insulating an old non-supporting brick wall
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I am currently restoring a home from the late 1800s. The front brick wall is not load bearing, but given it’s age it’s also not built to current standards. There is the brick veneer, and then the interior framing (with a fair bit of gap between the two).
I read the articles on insulating load bearing brick walls and the article discussing Zarring homes bankruptcy, but neither article really hits on my specific situation (non-load bearing, old wall assembly).
Would flash and batt be a preferred (cost effective) method here? Or if, we can guarantee proper drainage, would I be ok installing an interior vapor barrier on the interior of the brick and then using blown cellulose or fiberglass?
Also – the home is a row house with two interior shared brick walls. since the other side of those brick walls are all conditioned space – I assume there are less issues associated with insulating those walls, correct?
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Replies
What is your climate zone?
How much roof overhang, and how tall is the house?
What type (if any) sheathing is there on the exterior side of the studs?
Is there any air-barrier or weather resistant barrier (rosin paper, tar paper, etc) on the exterior of the studs?
How deep is the cavity between the brick and the studwall/sheathing?
What (if any) window flashing is already installed?
Matthew,
First of all, you may want to get a structural engineer to look at your house to confirm your hunch that the brick walls aren't load-bearing. In the late 1800s, it was typical for brick homes to have load-bearing brick walls. Even when wood framing was installed (in some cases, decades later) on the interior side of the bricks to hold insulation, the studs may not have been designed to bear roof loads.
Hi Martin, I may have misspoken - the wide brick walls carry the load for the floor joists, and I thought the roof structure was sitting on the framing, but I've asked for clarification from the GC. It's possible that the brick wall may be bearing the load of the roof.
Roofing overhang is rather standard, i'm overseas at the moment so not sure. This is a gut re-hab, so there is no sheathing/air barrier/etc... currently on the exterior side of the studs.
The cavity between the brick and the studwall is probably 2-4 inches. These old houses (in Pittsburgh) have a fair bit of unevenness to them.
Matthew,
As a first step, you should read this article: Insulating Old Brick Buildings.
The article should answer most of your questions.
If you still have questions after reading the article, you can post your questions here.
Great thanks. I read it before but I re-read it just now. The bricks are in good shape and I just blasted and repointed all of the joints a month ago.
There seems to be competing factors I need to consider. I am in zone 5, and for example -
"The thicker the insulation, the greater the risk of freeze/thaw damage."
This would suggest that maybe I should just put 2" of closed cell foam on the wall and call it a day, or not insulate it to be safe. (The house was already framed when I bought it so I can't put in rigid foam).
However, in a different article Dana Dorrsett points out that "Leaving the studwall wall cavities empty isn't recommended, since that allows fire to spread rapidly and may create a thermal-bypass channel undercutting the performance of your foam. It may be cheaper & better to give the brick a nominal inch of closed cell for air sealing & vapor retardency, then filling the rest with open cell foam or cellulose."
https://www.greenbuildingadvisor.com/community/forum/green-products-and-materials/26083/can-i-spray-closed-cell-insulation-inside-brick-w
So, if I don't insulate, or only do 2" of closed cell foam - then I have empty wall cavities that will be a fire risk, right?
Matthew,
You say you read the article, but some of your comments imply that you didn't. You wrote, "The house was already framed when I bought it so I can't put in rigid foam" -- but my article doesn't recommend the use of rigid foam.
It's very easy for changes to this type of building to result in freeze/thaw damage, so the first steps are to (a) evaluate the quality of the bricks and (b) evaluate the level of exposure of the walls to rain. If you've done that, you can proceed with whatever level of insulation meets your own appetite for risk.
If you haven't done that, you should hire an experienced consultant.
from your article -
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
Matthew,
Good point. I forgot about that paragraph, and I apologize for my earlier comment.
That said, you'll note that the document I quoted advises, "closed-cell polyurethane foam ... sprayed directly onto the brick masonry ... is the most effective, though costly, method for insulating the interior of brick walls."
Understood. I was just pointing out that I read the article :).
I can't even find the type of consultant for my area to even talk to them to figure out what i need to do... and the insulation companies seem ignorant as one quoted me cellulose.
Matthew,
I wish it were easier to give advice on insulating older brick buildings. It's hard to give advice over the internet for these buildings.
There is risk. In the worst documented cases, insulating this type of building has basically destroyed the building, so the stakes are high. I tend to approach these cases with humility.
If you have money in your budget, you can contact the Building Science Corporation in Westford, Mass., and ask them to consult on your project.
A roofing overhang of "...rather standard..." is a pretty meaningless dimension. Overhang depth & building height matter, since both bear directly on how much direct rain-wetting the brick experiences. If it's 4 stories tall and the "...rather standard..." overhang turns out to be 6" the moisture burden/risk is a lot higher than if it's 1.5 stories tall with 18" of overhang as the "standard".
Don't rule out cellulose. People have been insulating brownstones & row houses and in NYC with cellulose-on-brick, and it's not impossible in colder parts of NY. Chris Benedict has done quite a few buildings with dense packed cellulose directly on brick. Check out the pictures on p. 17 of this document on retrofitting a brick building in Pittsburgh, some of which is surely relevant to your project:
http://www.phius.org/NAPHC2013/UenoK-PassiveHouseMasonry.pdf
I'm sort of curious how this project turned out. It looks like ~20" or more of overhang, without obvious bulk wetting issues, fairly even apperance of the brick faces except where there's some potential splash back at the porch or ground levels:
https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/21370/masonry-interior-retrofit-foam-less-advice
https://www.greenbuildingadvisor.com/sites/default/files/IMG_8975.jpg
It's a two story building. I'm guessing 8-12" of overhang. will try to get a better handle on it.
I will also look more into dense pack cellulose. I, maybe mistakenly, assumed that there was some larger execution risk related to cellulose given the need to air seal appropriately. Curiously enough - an insulator here once pushed back against me doing closed cell and suggested open cell foam insulation. We proceeded in that manner. Is the logic there the same? Vaper barrier on interior through paint and caulking, let moisture dry to the outside.
A true vapor barrier on the interior would NOT be a good idea, but a "smart" variable permeance vapor retarder (or half-perm paint on wallboard) and something semi-permeable but non-wicking painted/sprayed on the interior side of the brick will probably be necessary to keep the cellulose sufficiently dry.
Post some pictures of the exterior, including details of any areas where the brick appears stained or deteriorated.
The open cell vs. closed cell decisions are really specific to the stack up. Open cell foam is a lot greener at half the polymer per R, and MUCH better on the greenhouse gas front (blown with water, not HFCs), but it also takes on moisture in some stackups. Even a thin half inch of closed cell foam on the interior of the brick will water proof it and air seal any cracks/seams in the brick, but will be about as vapor tight as standard interior latex on wallboard, which is semi-permeable. Combined with half-perm latex or 2-mil nylon (eg Certainteed MemBrain) as the interior vapor retarder the cellulose should't get soggy over the winter. But something like Sto EmeraldCoat is even more vapor permeable and probably an even better choice than flash-foam for sealing interior side of the brick if dense packing cellulose. Open cell foam is also high perm, but not sufficiently waterproof.
Matthew,
Proceed with caution. My article discussed Chris Benedict's approach (using cellulose):
"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."
I am grateful for Dana Dorsett's enthusiastic (and educated) suggestions, but lots of building scientists have been tripped up by problems with old brick buildings. If the bricks are of low quality, and there is a portion of the wall that gets wet, it doesn't take much winter weather to destroy the bricks. As I noted, I approach these cases with a lot of humility.
Clearly the safest approach in a full-gut rehab would be to build it as a cavity wall, with a 1-2" gap between the brick and the sheathing that is holding back the insulation, at the cost of 2-3" of "extra" wall depth. When taking that approach special care needs to be taken for detailing around joist supports, and if possible, provide an adequate convective ventilation path for the cavity, with vents at both the top & bottom of the wall. The venting part can be a pain to implement if it's a 3+ wythe brick wall.
Pictures of the wall will be useful for guessing just how much rain wetting it gets. If it appears to be quite a bit of wetting I'd personally be inclined to go with a cavity wall, and if there's a way to extend the roof overhangs that too might be considered. Freeze-thaw spalling damage on insulated brick buildings isn't super-common in climate zone 5, but it's not rare either. Insulating the wall from the interior heat source makes it run colder, making it more susceptible.
update - I reached out to a local engineering firm, an architect, and building science corp for a quote on doing an analysis on the brick.
I am getting a flash & batt quote, and we just got a cellulose quote that said properly installed tyvek would be fine for cellulose. I suspect he also meant something to deal with the moisture drainage on the other side of the tyvek wrap.