The idea I kept gravitating towards was that our heat should be free. Basically, to make the house as efficient as possible, with minimal external energy input. However, our budget is..... small. So what basic and affordable home design strategies can we employ?
Earth-Sheltering: 4 feet underground, the earth stays a constant 50-55 degrees year round (or so). We can use this to our advantage for a serious energy savings. Know how your basement stays nice and cool in the summertime? The steady temperature of the earth will help temper the conditions in the house. Of course, the reason many people's basements also feel cold in the winter time is that they are not insulated to the ground - our foundation will be well insulated to around R30. You can kind of think of our house design as a walkout basement without the upstairs.
Passive solar design: Even in cold, cloudy Michigan, the sun is an amazingly powerful thing. We want to capture this energy in the winter time, but not the summer time. We can block it in the summer pretty easily, with roof overhang design and window shading. So we still want to orient the house to capture solar energy for the other 2/3 of the year. Thus, the bulk of the houses windows will be on the south side, and the roof will be a single-slope design facing up to the south. With the right overhang and roof slope, this lets the winter sun penetrate deep into the home.
Super-insulated envelope: This is one area that we knew we needed to spend a bit more on. Once that free solar heat comes into the house (or from any other heat source), we want to keep it there! Using thicker 2x6's for our homes exterior walls, as opposed to 2x4s, gives an extra 2" of room for insulation fill. Not to mention making the house more solid. We'll cover every external surface of the house with more polyisocyanurate foam insulation to provide a thermal break on all conductive surfaces. A roof built with 2x12 rafters gives a lot of room for insulation, reaching nearly R50 when all is said and done. mmmmm.... toasty.
High-tech windows: Ok, this was another important expense as well. Argon filled double pane with low-E coating. Insulated frames. And we chose casement style windows for their superior sealing when closed and locked.
Slab-On-Grade Construction: This one seems to raise eyebrows and require explanation. No basement?!? No. With our passive solar design, the point is that sunshine can directly hit and charge the slab. It provides a high-mass, high heat-capacity element within the home to help regulate temperature. Below the slab, 4" of rigid foam insulation board keeps the slab from losing much heat into the ground.
Masonry Woodstove: Well, we may cheat the budget a bit and install a conventional cast-iron woodstove to begin with. But we hope to get to a high-efficiency, high-mass masonry woodstove reasonably soon. The key here, is that you can burn a small wood load really hot and fast (thus at higher heat-conversion efficiency) and absorb that heat into the big mass of the stove (and radiate it slowly into the house thereafter) instead of releasing most of it out the chimney.
Most of these strategies are pretty simple, as long as you design for them. The end result should be nearly free heat, even in this frigid land of Michigan. And with the eventual addition of a modest solar array, we should hit net-zero fairly easily. But we'll just have to see, so wish us luck! I'll detail all these features in coming posts as the home build takes shape.
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