Once the joist structure for the larger of the two rectangles that comprise this building was complete, I laid subfloor. We used an "engineered wood product" that is supposed to be moisture resistant. Unlike the joists which were cut within twenty miles of here and milled into lumber just five miles away, this came from a factory which as far as I can make out is in Charlotte, North Carolina.
Not only was this not local, but at $30 for each 4 by 8 foot sheet, it was also expensive. Yet it had to be. I needed a moisture-resistant subflooring material because we typically get some heavy downpours here in Maine during the summer, and it would be a few weeks to a couple of months before I could get a roof over this structure. This stuff came with a hundred day warranty -- it could be exposed to the weather for at least a hundred days without damage.
Back in the day Maine-cut hemlock or pine "one-by" or 5/4 ("five quarter", ie, or 1.25 inches) subfloor boards were of course naturally moisture resistant, and so we could have used a local material instead. But I knew from hard experience that those kinds of more natural materials are too uneven for modern flooring products, and Aimee wants a "proper"flooring product. Laminate flooring is generally best for folks who have lots of animals, because it can be very easily swept and it doesn't hold dog and cat hair. (Hardwood is even better but prohibitively expensive.)
Again, we know this from hard experience. Back at the Straw Bale House, I "improvised" pine floor boards by recycling two by six planed pine boards materials from an old chicken barn. The resulting floor looked fine (for the first few weeks of use) but had all these cracks that just sucked up dog hair and other "accidents". The only way you could keep down the smell of any such accidents was to periodically rinse the whole thing with bleach water. Since then, considering each subsequent set of Bale House residents has had multiple dogs and cats, this situation has just gotten worse and worse, to the point where I'm thinking about sanding and filling the whole floor and covering it with a hard polyurethane varnish.
That was back in my "heroic" days of building material recycling. I got those boards for $2 apiece, but had to pull twenty or thirty nails out of each one. I don't have the energy for that kind of recycling in this building project. If I had to pull nails out of floor boards, it would take another summer to build this place. The Straw Bale House took two summers to get closed in and insulated.
Once the subfloor was down we had a "line" for the height of the finished joist structure, so next we covered the foundation walls with foam board insulation up to this height, gluing the edges with spray foam. This effectively air-sealed the whole basement/crawl space area, except for the exit route for the sewer pipe, which will be sealed with spray foam once the sewer and air duct are in place.
Although you can't tell from this photo, which was taken late in the afternoon, the foam board is a "hot" pink color. Much of this too-bright pinkness will get hidden by dirt, as we back fill the basement hole. You can see from this picture that I've begun to fill the hole in already on the north side. Today I'll do the other three sides, using the Kubota tractor.
What foam board remains visible above the dirt will get a coating of chicken wire and surface-bonding plaster. But that job can probably wait for next summer. We'll live with pink for now.
The foam board insulation was also expensive. We used two-inch closed cell foam, which has an "R-value" of ten. It took around twenty sheets to cover the entire foundation, although there are a lot of off-cuts left over that can be used in the walls later. At $33 a sheet, this cost nearly $700. We'll also install a layer of this material with underlayment on top under the laminate floor -- as a "floating" floor insulation, and air-seal it all with the bubble wrap sealing material that comes with the laminate floor. That should be enough to separate the house space from the crawl space more or less completely in terms of both air-sealing and insulation.
Most builders don't insulate and air-seal foundations and basements to this level, but if you want to build a passive solar house, you need to air-seal and insulate to a very high level indeed.
In this case, we also want to run water pipes in the basement area, and so need to protect them from frost. If it wasn't for that we could just insulate and air-seal the subfloor, but that won't do here. We need to keep the basement area from freezing.
That big rock ledge will help even out the crawl space temperature over the seasons, but it may also import cold at the point where it's not very deep. There's a point on the north side where the rock is essentially at the same height as the ground surface, although I plan to add a few inches of dirt there to give it some cover.
Later today I plan to run a wire down in the crawlspace and put in a couple of basic lamp holders with sixty-watt incandescent bulbs. Not only will these light the space for doing work down there -- fitting the sewer line, water pipes, and air duct, but they'll also provide enough heat to keep the pipes from freezing if the house is ever left shut down in winter.