Weekend 2: Subfloor finished!
This weekend was much better for working outside in, as it was a little breezy, and sunny but not beating down. Metal flashing with sun on it is fairly blinding.
Bought the 3/8″ plywood and laid it down, feeling much better about that than only flashing. Finished boxing in the 5 compartments of the trailer, making sure that we “boxed in” the spots for all of our plumbing drains (in our case, the tub and the two sinks, as we will be treating greywater on site for irrigation). No toilet drain needed, as we are going the humanure route (I’ll post pictures of our potty at a later date). We also ran 5/8″ all-thread through the outside stringer in the main compartment, and through both boards in the fender compartments, bolting everything together securely. Another nice feature of the Iron Eagle trailer is that they ask you where you want your bolt holes, and weld washers in place on either side of the box beam so that it is powder coated with the rest of the trailer. That way there is no damage to the finish, and nothing can rust!
A side note: if the ceiling under your loft is only 6’2″-6’4″ as most are, did you think about how your tub drain sticks out? Don’t want to hit your head on the ceiling because you forgot to account for that stupid drain outlet when plumbing in. Of course our tub drain landed exactly on a floor joist, so we had to cut it and box the area in, but better realizing it now than later…
Once the drains were boxed in, the floor screwed together and bolted to the frame, it was time to “sheep and sheet” as we said! The wool smelled like clean sheep, and no gloves, respirator or goggles are required; even the kiddies helped “fluff fluff” the insulation:
As we insulated each compartment we sheeted over everything with 3/4″ thick subfloor plywood, which is expensive but really the best; PAD and Tumbleweed agree on this. I thought maybe 1/2″ thick flooring would be fine, to save on height, but everyone says you’ll feel the floor sag if you do anything less. So shell out for the 3/4″ sheathing!
We were frustrated at first that it took us two whole weekends to do the subflooring, but many tiny housers say it took them more time too, so we are trying not to panic. Since we are doing a curved roof that will probably also slow us down a little as well. But she sure does look good, all fleshed out with no more ribs showing!
Weekend 1: Subfloor Underlayment and Sealing
So we hauled the trailer over the mountains with much trepidation, and arrived without a problem. The trailer actually tows very well. Everyone who sees her says she’s beautiful! Here was the view welcoming us:
First step, laying the subfloor. Since we have fancy extendo-crossmembers we actually have to frame in 5 boxes, two on either side of the fenders plus the main area. Which brings us to the first conundrum: what type of underlayment do we want? It needs to be strong enough to handle the errant stick, keep out moisture, rodents, and other would-be residents, and protect the floor insulation.
Tumbleweed recommends aluminum flashing nailed to pressure treated lumber stringers laid on their flat side, framing, followed by extruded polystyrene foam with expanding foam insulation to fill in the cracks. Nasty chemicals, the whole lot, and would definitely off-gas! And we discovered that to use aluminum flashing would cost $200. Ouch.
PAD recommends marine grade coated waterproof 1/4″ plywood, followed by wool insulation (treated with only borax). We really like the wool idea (especially since it is grown in Oregon, and sold in Ranier!), but coated marine grade plywood is, again, nasty stuff. In general, adhesives and sealants are the hidden bugaboos for MCS-ers trying to build a house, and marine-grade plywood fails on both counts, although it is thin, lightweight, and waterproof. Traditional construction adhesives all typically use solvents that off-gas, at minimum, a lot of formaldehyde. Now, the pig-headed construction orthodoxy will argue that natural wood off-gasses formaldehyde too, and technically they are correct, so if you see a wood product that says “No VOCs”, they are lying. However, the RATE and AMOUNT is so tiny as to be almost unmeasurable, so as close to natural wood as possible is the way to go.
So about plywood. Interior grade plywood often uses urea-formaldehyde adhesive, which is the worst of the adhesives; ironically the very stuff you would have closest to you, breathing in the goodness. No surprise, as once again, most construction adhesives are derived from fossil fuels. Exterior grade plywood typically uses phenol-formaldehyde, which still off-gasses, but at a much lower rate. You can find interior plywood at greater cost that is urea-formaldehyde-free (meaning they use phenol-formaldehyde), but you cannot find a lo-VOC exterior grade plywood. At least we couldn’t. OSB (oriented strand board) is, along with particleboard, the nastiest of all the plywoods, heaviest, and turns to oatmeal when wet, so no OSB anywhere in our house. It’s only benefit in construction is that it is a little cheaper.
So we went for the least of evils:
Galvanized steel flashing, which cost half as much as the aluminum, a 3/8″ thick sheet of CDX (a type of exterior grade) plywood on top of that, followed by our stringers of 2×6″ pine. To seal the cracks in the flashing, we used a type of adhesive flashing tape… joy! Back to the computer, looked it up, and there are two large groups of flashing tapes, those made with asphalt and those made with butyl rubber. Apparently the latter is not good, but not terrible as it does not off-gas any VOCs unlike asphalt tape. Here’s the article for your interest: http://www.bestmaterials.com/PDF_Files/flashing-tapes-manual.pdf
And for your information, metal flashing is a pain in the butt to get tight enough if you are just screwing it straight into your cross-members, which is probably why Jay used the stringers as he did. We found out the hard way that it leaves lots of gaps around the edges, and a lot of gaps in the middle if it is not perfectly tight, which is fine if you’re using polystyrene board, which no creature is terribly interested in. So we added the 3/8″ plywood the weekend after, as we thought it would be better able to protect the wool insulation, and likely why PAD used a solid wood underlayment. Next week: finish the subfloor!