Renovated foundation wall detail
I am renovating a duplex in Montreal, Canada (Ashrae climate zone 6: hot, humid summers & cold, dry winters).
To get the minimum required ceiling height for a basement rental unit, we are going to chip the existing footing back and install a new basement slab level with the bottom of the footing (see pic). This is a common reno detail but it seems there are different practices out there, esp. with regards to drainage.
I would like general feedback on my approach witj regards to 1. basement drainage and 2. insulation and vapour measures. I have also noted some specific questions below.
1. For drainage I plan to install a waterproof membrane out front with a piece of rigid insulation or dimpled drainage mat over top to protect it. Given the underside of slab will be below the top of footing, I am not considering french drains (they would be above the slab); rather I am proposing to install a dimpled membrane underneath the slab, on top of a few inches of gravel, that will slope to a central drainage trench (course gravel covered with filter fabric) that will be in turn emptied by a sump pump when necessary.
2. For insulation, I plan to run horizontal rigid boards just beneath the new window wells 4′ from the foundation wall to keep the bottom of the foundations warm. On the interior of the basement I am showing spray insulation with the studs installed 1″ from the face of the foundation to avoid thermal bridging and moisture build-up in the wood.
Should I avoid closed-cell foam insulation given there is a waterproof membrane on the front of the foundation (will it trap moisture within the wall?) and chose open-cell?
Should I avoid installing vinyl flooring (effectively a vapour barrier?) on the basement slab if the dimpled membrane (lapped and taped) is acting as a vapour barrier underneath? If so, any recommendations on thin vapour-permeable flooring finishes?
Any tips on capillary break details under the studs and drywall where they meet the existing concrete?
Any additional tips are much welcome. Thanks!
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