My latest thoughts for walls for my "dream house"
My dream house will be located near the northern tip of Michigan over looking the shipping channel. The back will face north and have lots of windows for the view, I know terrible for heat loss but that's what the boss wants. The good news is the front, street side, will face due south and can hold lots of PV. I'll strive for exceptional air tightness and aim for r60 ceilings, r40 walls r30 basement walls and r 30 below the basement slab (using perlite). I'll incorporate a masonry heater but heat with a Mitsubshi hyper heat minisplit. I've looked at oh so many walls and, I hope, finally settled on "the one". Double stud framed out of 2x4 16" OC with 3 1/2" between walls. I'll plan to make both load bearing to accommodate my large roof and snow load requirement, discussed on another post. The exterior must be brick to please the boss! I'll use Ambrico EZ wall, a thin (1/2") brick glued to steel substrate panels. Under the panels is Greenguard DC14, a 1/4" XPS product that has drainage channels on both sides, a low permeability to block solar driven moisture and add r1 to the wall. Under the DC14 is Tyvec covering 1/2" structural rated fiberboard that adds r 1.3. The stud cavities are filled with R15 Roxul comfort bats the inter wall space is filled with r15 Roxul comfort bats for steel studs. The inner wall, is sheathed on it's outer face with 1/2" plywood and has an interior service cavity filled with Roxul r 15 bats.. The interior is 1/2" drywall. I'll use aligned studs for greatest condensation immunity in winter. The plywood will be carefully detailed as an air barrier and is the only moisture control layer. With a mid cavity r value of 47.83, ignoring drywall and air films. and a mid stud r value of 26.6 at 20% framing fraction, which I'll try to beat by adopting principals of advanced framing even though I'm 16" OC with double top plates, I calculate r 41.2 assuming pure 1 dimensional heat flow and 40.9 assuming the plywood is a constant temperature plane allowing unlimited crosswise heat flow in the plywood, like it had an aluminum foil layer. At 25 % the results are r39.83 and r38.6 And the wall is only 12 3/4" deep including brick. The construction sequence will be a bit unconventional as the outer wall will be erected unsheathed and remain so till after the first round of air sealing testing ( which may begin with temporary " plugs" in the windows. I'm working on details of the transition from concrete basement to wood walls trying for minimum heat loss economically. I'd like to consider the wall plan finalized so if you see that I did something dumb PLEASE speak up.
Posted Sun, 03/10/2013 - 20:26
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