I’ve been asked to design an attic remodel for client’s 1950’s Cape on Boston’s North Shore. Presently the attic is unfinished and unheated. She wants a new roof, siding and windows, a golden opportunity to try a DER. Also, she would like gabled dormers on the front and a shed dormer in back to increase headroom and furnishing flexibility.
Since so much of the roof will be modified, and the existing rafters are 2×6 @ 16″ o.c., the entire roof – structure and all – will be removed, affording some serious opportunities to optimize insulation as well as air and water barriers.
Her budget does not currently allow for replacement of her atmospheric, oil-fired forced hot air system, so it will still vent into a masonry chimney that penetrates the roof on the back side of the house. The water heater is electric.
My biggest concern is: if I specify exterior polyiso on walls and roof (unvented attic), spray foam at the rim joist, rigid foam on the interior of basement walls, might I “over tighten” the house and risk spillage/backdrafting from the furnace?
Other concerns: the current GBA video series about adding polyiso to the roof shows 2×4’s over the polyiso…is the space between them filled with more polyiso, or is there some sort of vent channel to preserve a cold roof surface?
Any thoughts are much appreciated; this is all new(ish) to me.
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