I have a roofing / deep energy retrofit question
I have a roofing / deep energy retrofit question. I’m just beginning a deep energy retrofit as a retirement home on a permaculture garden-farm project in northern Alberta, Canada (ASHRAE Zone 8). Tomorrow we are moving a 42’x28’ bungalow 200 km.
As it needs a new roof (old shingles are stripped to sheathing and house tarped at old site), the current plan is to chainsaw the eaves, then apply air/vapour barrier, insulation (either Roxul ComfortBoard or EPS) to exterior walls, preserving as much interior space as possible.
Exterior cladding is a mix of lightweight metal sheeting and locally milled [lumber], treated using “shou sugi ban” technique both on vertical furring (metal is recycled, locally milled [lumber] is from trees harvested on site). Windows will be installed with a strapping/built-out buck system and flared walls on the inner wall with attention to air circulation, passive solar in winter, daylighting and connection to the outdoors.
Just not sure what insulation/air barrier method would be best for the roof? A metal roof is planned (not standing-seam due to budget) but good quality. It’s a simple roof, 15% slope (5.6/12). The ceilings are low (8’ from top of subfloor). It’s built with rafters – kind of a weird design – collar ties with vertical struts angling toward center fastened to the joist (this is no heritage home, but an old sturdily built prairie shack). There is very limited space between top plate of eave and underside of roof deck. I’ll know exactly how much in a couple of days. So far, everything is sound.
While I’ve reviewed many resources, the most recent and helpful has been http://www.buildingscience.com/documents/guides-and-manuals/gm-mass-save-der-builder-guide. I recognize the most effective upgrade might be an unvented attic with exterior roof insulation. However, I’ll be installing a wood cook stove with a chimney that will exit near the ridge. And that makes me wonder if an unvented attic is the best? I’d like to hear any and all feedback on roofing insulation/air/vapour barrier assemblies.
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