Do I really need 4 minisplits?
My wife and I own a lot in a development in the Pacific NW (Zone 4c), and we are planning to build our retirement house on it. We have never built a house before. Our projected house (which we designed ourselves) is 1,833 sq. ft. on one story, a modified California-style bungalow, as simple in geometry as we could make it.
The developer of this neighborhood is a good guy, and he wants to work with us; however, he is not really into “green” building per se. He aims at giving solid value for money, and he succeeds. We tend to prefer going with him, opposed to getting an outside bid, since he lives in his own development (built on land his family has owned for generations) and stands behind his product. He is listed as an Energy Star builder, but that standard is too wimpy for my tastes.
He has quoted us an affordable price for the house (VERY important, since this is all the money we have), but basically he would put up a stick-built house (well-built we have no doubt), in the traditional West Coast manner: ventilated crawlspace, under-floor R-19 insulation, 2×6 walls, plenty of wood (no Advanced Framing), R-19 fiberglass walls, truss roof with R-38 attic.
For HVAC we prefer minisplits (the local minisplit dealer lives in the same development), and for our 1,833 sf house the builder has budgeted for 4 minisplit units (probably the smallest Mitsubishi Mr. Slim). I, on the other hand, would like a sealed, insulated crawl space (and rim joist) per BSC recommendations, 2×6 walls (well-sealed) with R-23 Roxul rock wool or R-21 fiberglass, 1.5” to 2” polyiso sheathing (yielding a nominal >R-30 wall), and the attic insulated to R-49 or R-60.
The sealed crawl I think I can talk him into: the price should be a wash. And the sealing of air leaks is something he’ll surely do. But I think the polyiso foam with siding nailed to vertical battens will be a sticking point. I don’t think he’s ever built that way before, and I’m pretty sure he’s going to tell us it will cost a lot more money, what with the added trim-out details around the windows, etc.
My thinking is this: why should we put 4 minisplit units into a small house if we can put part of that money into improving the thermal envelope? (I know another builder, by the way, who is hungering to build us a hybrid ICF foundation-SIP wall structure. But he doesn’t live in the neighborhood.)
Your advice, please, especially about the minisplits. How many do I really need in a house of this size?