Am building our SW facing energy-efficient home (1850sf+/-) shortly: Reddiform ICF for all outer walls from footings to roof, stuccoed, 3″ Dow SM under basement slab, all joints taped, infloor hot water radiant, engineered 20″ wood floorjoists which are topchord bearing on LVL ledgers for clearspan basement, with extra horizontal strongbacks to make a truly monocoque floor system, stapleup radiant tubing, 7.5/12 roof trusses 16″ o/c with 4′ overhang, single attached unheated garage, hardcoated windows = 6.4% of wall area, 2 freestanding see-through gas fireplaces (supplementary heat & esthetics, 1 per floor). Am also considering Solatubes ending in ceiling lightboxes to provide indirect mainfloor daylight. All windows are inset are much as possible, with window openings chamfered about 40 degrees. All plywood sheating is glued & screwed, and we will be using an HRV with ECM motor.
Here, in Ontario, Canada, code requires vented attic insulated to R31, or if not vented, R50 under roof. This house will be very tight, and I do not want a vented attic; would rather have 5/8″ plywood sheathing totally covered by waterproofing, and, under the steel roof with ridgevent, I would like to install vertical 1 x 2 strapping, then horizontal 1 x 3 roof strapping, to have sufficient venting. I’m wondering how best to insulate under/over the roof: 3′ or better DOW SM/Roofmate foamboard,
sprayfoam, or mineral insulation? I’ve considered extending the outer housewalls upward by installing plywood kneewalls between each truss, and covering in sprayfoam, which will also seal any very small leaks we may miss.
Advise or criticism are both welcomed.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part