Brick house insulation
First of all, I wanted to wish everyone Happy and Prosperous New Year!
I would like to ask for an advice regarding a wall cavity composition. I am in Westchester County, 30 miles north of New York City, climate zone 4. I am about to acquire a brick house (tiny brick, maybe 2-3 inches thick). Single wythe, I believe. I think that brick is just decorative and is not load bearing at all. Only cinder blocks in the basement support the floor joists. Second floor ceiling joists are supported by wood framing.
I was trying to educate myself as much as possible on the subject. I have read https://www.greenbuildingadvisor.com/blogs/dept/musings/insulating-old-brick-buildings and other publications regarding the subject. I know that the best method is to insulate outside, but this does not seem to be an option as of now. As per inside, I understand that the best method is closed spray foam, but I would like to avoid that as well.
I think I will own a building with low risk factors, and may decide to go ahead without hiring a consultant. The building has no signs of exterior water damage, without any deteriorating bricks, and with flashings that do a good job of keeping rainwater off the building.
It will be total demolition inside only. After demo phase is completed, I would like to insulate as well as possible. I am not 100% sure, but as far as I was able to see walls are made of 2×6 studs. I think studs might be in direct contact with the brick, or there might be a very tiny space between (the house built around 1950). I know that according to recent research wood should not come into direct contact with brick, but it is a retrofit, and I will not be able to redo the framing, so whatever is there stays (if there is more space between studs and wall, I would slide insulation behind studs. I was planning to adhere 2 inch thick Polyisocyanurate (Thermax) R13 boards (due to all horror stories about respiratory problems, even when jobs were done professionally, I would prefer not to have spray foam in the walls, as far as I read Polyisocyanurate does not contain the same chemicals as spray foam, please correct me if I am wrong), cut them to snug fit, adhere them between 2×6 studs, tape them etc.. In case there are any cavities left, I would fill them with a canned spray foam (minimal quantities are ok). Then I was planning to use Roxul Comfortbatt R15 on the top of the board. Total R value (2 inch board, and 4 3.5 inch roxul) should be about 28, minus whatever I lose due to thermal bridging etc. I am fine with that. I plan to finish the wall cavity with a drywall.
• Does my idea make sense? Would you plan the wall cavity differently? If so, how?
• Should I apply liquid-applied air barrier, on the inside, to the brick first? Like a brick sealant or so? I believe I read that GBA does not recommend this. Is this correct?
• Is Thermax Polyisocyanurate appropriate material for my application? If I look at “Calculating the Minimum Thickness of Rigid Foam Sheathing” it seems that its thickness is well enough for my climate zone, however in places where studs are, it may not be thick enough. Can this cause moisture problems? It seems that the wall would be water impermeable, perhaps except where the studs meet the bricks, or “almost meet”? I admit this is pretty confusing, and I understand why closed cell foam is the recommended solution here.
• Should Polyisocyanurate foil face be installed towards inside or outside of the wall? As far I was able to understand, it should be on the inside. Is this correct?
• What about the vapor barrier underneath the drywall? Would my Polyisocyanurate create a vapor barrier on the outside side of the wall? I read that it is not advisable to have two forms of vapor barrier (the rigid foam and the poly) with any kind of cavity or other material in between because condensation will build up between them. I was thinking about installing MemBrain Smart Vapor Retarder & Air Barrier Film underneath the drywall. Is this a good choice for my application? Would I create aforementioned problems? Perhaps I should skip it?
• What about the vapor barrier in the ceiling? Should the vapor barrier be installed on the ceiling too (ceiling will be insulated with R30 Roxul, and I may add cellulose on the top of it later, no boards here)? I guess in this case double vapor barrier problem would not exist so I could use MemBrain Smart Vapor Retarder & Air Barrier Film underneath the drywall without worries?
• Can I use the same wall cavity composition in the basement? 50% of basement walls are above the ground, so it is like a half basement, as the house is built on a slope. The basement walls are made of cinder blocks. I would be able to redo the farming here (on some walls it does not exist at all), and adhere boards to cinder blocks in continuous manner and thickens without any problems. Assuming correct board thickness, I see that vapor barrier is not recommended in basement applications, correct?
• Are there any special requirements when it comes to bathroom walls? There is about 5 feet wide outside bathroom wall. Should I insulate this part differently? If so, how?
• What material should be installed inside of internal bathroom walls? Some sort of faced insulation?
• If all else fails, and I have to go with spray foam, would 2 inches thick, complemented with 3.5 inches of roxul be sufficient?
Any question and suggestions are very welcome. Any help is greatly appreciated. If I got it all wrong, please tell me what would be a recommended wall cavity composition in my situation. I am trying to achieve the highest R value, as well as I prefer not to use a spray foam and cannot insulate from the outside. Big thank You!
I was following the below referenced document: Measure Guideline: Installing Rigid Foam Insulation on the Interior of Existing Brick Walls H. Natarajan, S. Klocke, and S. Puttagunta