WW2 era 1.5 storey retrofit – which insulation type/method?
Good day GBA!
First I wanted to express my gratitude for this forum. It is truly an invaluable resource!
I’ve read all the articles, blogs, and Q&A’s regarding my objective, but I have not been able to find what I’m looking for with regards to my current situation.
A bit of background here… I believe I am in climate zone 7 (Thunder Bay, Ontario). Ive got a WW2 era 900 sqft (newspaper found in the walls from 1948) 1.5 story home with virtually no roof overhangs. all framing (wall studs and rafters) is full dimension 2×4’s, aluminum siding, thick felt paper, 1×6 shiplap plank siding, and stud bays filled with wood shavings.
My grand plan was to do a complete energy retrofit to include 6″ exterior recycled polyiso on the walls and 8″ on the roof over a complete application of peel and stick, followed by new windows, rim joist sealing, and re-constructed roof overhangs. Unfortunately the reality of that undertaking is fading.
I’ve began working on the small second story from the inside. I opened up some walls to discover several layers of wall paper, other paper/cardboard products, a couple layers of gypsum, and stud bays to contain massively settled wood shavings. The shiplap plank sheathing has shrunk considerably showing large gaps between every board, revealing a heavy felt on the exterior of the walls and the sticky roof underlay on the roof. The knee wall only has 1.5″ worth of wood shavings. The small attic had some fluffy rock wool blown in, and is not vented.
My immediate plan is to gut the entire second floor interior, as the current layout is useless and the full bathroom needs work.
As far as an insulation/air sealing plan, keeping in mind the possibility of doing exterior rigid foam later, I understand that I should use a permeable insulation on the interior to allow for inward drying. I get that the most ideal plan would be to use closed cell spray foam to tackle air sealing and insulation all in one..but I want to avoid a future foam sandwich that can’t dry in either direction. I have noticed some dry rot in the plank sheathing as well as evidence of water entry. I will be replacing some of the planks as best I can from the interior. My roof is essentially an unvented cathedral ceiling.
Option 1 – (should be the most economical/simple/quick – R13+ R8) Install batts of Roxul in the stud bays (walls and ceiling), plus 2″ of rigid foam on interior of studs. Cons: batts would probably get wet from exterior as there is no continuous barrier. Q: can a poly/smart barrier be used between fluffy insulation and studs/sheathing to prevent water damage?
Option 2 – (expensive, but possibly best performance – R18+R8) Full application of closed cell spray foam, with or without additional interior rigid foam over the studs. Cons: would be dangerous to do exterior rigid foam later ,and replacement of rotten sheathing planks later would be difficult due to adhered foam.
Option 3 – (time consuming, but fairly economical, good performance – R16+R8) Cut and cobble EPS with or without additional continuous interior rigid foam over studs. Cons: obviously very time consuming. The use of EPS would allow some interior drying if I did decide to do exterior foam in the future.
Unfortunately I do not have recycled rigid foam available in my area. Plan 1 is my intention at this point, but I am a little concerned with putting fluffy insulation in the stud bay with no real continuous barrier on the exterior. The foam on the interior would be detailed as the air barrier finished with either drywall or a panel board/hardboard. Canned foam would be used to help with this.
I would love to be able to do this job 100% “properly”, however budget doesnt allow for that at this point. I get that the total R value, especially for a cathedral ceiling, will be dramatically low for my climate zone, however it will still be a massive improvement from the R3-4 equivalent that was in there before.
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