Insulating a 100 year old triple brick home
I recently purchased a 100 year old triple brick home with brick foundation that I am completely renovating. I did a lot of research on insulation and came across your article on insulating old brick buildings. I have decided to insulate the walls with 2.5″ of closed cell spray foam and I am having the bricks repointed on all sides and having new sills and windows installed.
My question focuses more on the flat roof. I have a flat roof that is vented and covered with an elastomeric membrane. I will be using air tight ceiling boxes for light fixtures and will seal around plumbing vent and roof drain as best as I can. I was going to install r-40 batt insulation with no vapour barrier or maybe just a vapour barrier paint, but after doing more research, it seems insulating from the outside with rigid foam is a better approach. The roof is relatively recent and a full replacement is not in the budget. What is the best way to insulate in the interim? I can spray foam the underside of the roof decking with about 7″ of spray foam, but that will leave no air gap and not sure how that works with the existing vents.
Thanks for your help,
Jason
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Replies
Jason,
I don't know anything about insulating old brick buildings, but Martin' s blog seems to say you need to be careful how you go about it: https://www.greenbuildingadvisor.com/article/insulating-old-brick-buildings
Once you use either roof top foam or spray foam on the underside of the sheathing, it needs to become an unvented assembly. The vents need to go, and the perimeter of the roof space requires good air-sealing. Depending on how high the space (mini attic) is it will need to be conditioned too.
Hi Malcolm,
Thank you for the response. I've read Martin's blog several times over the past several months and with some caveats, he seems to say that closed cell spray foam is acceptable as long as we can control water and don't apply too much to still allow some drying of the bricks.
For the roof part, what do you mean by the mini attic will need to be conditioned too? The roof is supported by 2x6 rafter embedded into the brick. I sistered those rafters with 2x10s and install supports to support the roof structure since I anticipate having more snow on the flat roof after it is insulated. I have about 6" to 10" between the ceiling and the roof deck depending on the slope of the roof.
Jason,
Here is the link to the article you need to read: "Insulating Low-Slope Residential Roofs."
Your plan to install closed-cell spray foam (note: don't use open-cell spray foam) on the interior side of the roof sheathing will work, as long as there are no vent openings between the insulation and the interior of your home.
Hi Martin,
Thank you for the response. I have 3 vent openings currently that I am closing as part of the insulation work. I will use closed cell spray foam to get about an R-40 and, if necessary, add rigid foam on the outside when I redo my roof in the future.