[MN Renovator]

I'm living in a house I bought in the middle of 2010. I like the house and I've air sealed it pretty well and have a few more gaps that I know about that I'm taking care of this month. I got to thinking about what I'd do if I moved to another place to build a house.

When I do it all over again and eventually build a new place for myself instead of buying the mistakes made by builders and the original owners who chose the place and its location. I want to build it with similar thinking to the Alaska zero energy house but I won't need nearly as much insulation and realistically I don't think I need a huge hot water storage vessel to store summer heat through the entire course of the winter.

I'm thinking that I'd like to go with 12" dense pack cellulose in the above ground walls. I think I'd go with foam overhead and try to get close to R-75 as I can get overhead with a lighter colored metal roof and have livable space in the attic instead of lose that room to being an empty space, all glass larger than 2 feet per side would be on the south side of the house and enough thermal mass built in to do a decent job of slowing the big temperature swings between day and night.

I'd want to go with Fujitsu's 9k 26 SEER 12HSPF ductless minisplit unit installed with a very open upstairs floor plan with living/family room and kitchen upstairs with stairs in a non obstructive location at a corner of the house and bedrooms and theater room in the basement where the temperature stays more stable year round. By going with an open long throw floor plan one ductless minisplit can cover the entire space in regards to air flow.

I think that having a livable conditioned attic or at least accessible storage space and a finished and conditioned basement is key to making a small house work. I'd be looking for a interior floor size of 700sq ft or less, with a 700 sq ft size for each level, I could essentially have almost 2000sq ft of space, attic for suitable storage and bedroom expansion if wanted, kitchen and living space suitable for guests, and theater, office, and bedroom space downstairs with a bathroom on the main floor and basement. I would have the 9k minisplit be the only source of heat and cooling for the house. I think this would work because if my current house can handle staying the same temperature at -20f(-29c) using 26k BTU/hr when it had R11 fiberglass in the walls, plenty of infiltration, an unwrapped skylight, bad directional facing and big windows on the wrong sides of the house I'd imagine a house at 65% the volume and good design with plenty of thermal mass shouldn't need that much. An inside outside difference of 0f(-18c) and 70f(21c) inside is 20k with my current house. 65% of the foundation size as interior size would mathematically be 13k without factoring less windows and better positioned windows or increased insulation. Worst case I fire up a space heater, a toaster oven, a hair dryer, or snuggle in my bed with my heated mattress pad and watch TV on a cold night. 600sq ft floor space would save more and realistically its all I would need and I wouldn't even need the really attic if that complicated things too much but I think that wasting an attic would be wasting a great storage space that I currently use my basement for.

I'd have a small HRV and seal the house to the passive house 0.6 ACH50 standard when it is built, which I would imagine should be that difficult with a small house, a local builder at a 'green expo' said their houses are all 0.6 ACH50 blower door tested with R26 walls, R60 ceiling, and R20 foundation. He was talking about how it doesn't cost them that much to make these improvements over any other house and they average a 46 HERS while energy star requirements bring a HERS rating to 85.

I also had another radical idea, what if I built the house so the main floor was sunk in at the same level that a split-level lower floor is, that would save me from exterior heat and extreme cold exposure through the walls and I'd probably only really need 2x6 construction with less insulation. The house would look weird but if I was retired(not close enough to that yet though) and didn't need to commute to work then I could live far enough out in a rural area where there is farmland and I could have distance from the neighbors and rent the rest of the land to a neighboring farmer so it would look like I was just a farmer with a small house sunk 5 feet into the ground.

Am I way off base with my ideas for building a fairly efficient house? What do you think?