Seattle - Insulation
It seems like there are no good insulation choices, and we picked cellulose because it seemed like the best option, both for performance and environmental reasons. Of course the reality is that its just shredded recycled paper treated with borates to prevent mold and reduce flammability. We had some concern as to whether the borates stay in the cellulose over the long term, and the general consensus seemed to be yes, but not necessarily an emphatic yes. Even if the answer is yes, the idea of using a product that would seem to be so susceptible to fire and mold seems like a bad idea. Of course wood and straw also burn and also are attacked by mold, but at least they have a much smaller surface area.
Although the original plan was to spray the cellulose in, our deep wall cavities and wide framing spacing resulted in immediate blowouts- there just wasn't enough wood for the insulation to stick to even after we added blocking half way up the wall. While this method may perform well in shallow walls, it was totally bogus in our setup, even though they did get it to work in some places. The alternative method is to cover the wall cavities in a light fabric, pop a hole in each bay and blow insulation in ("dense pack"). In this method it would appear there was virtually no way any settling would ever occur because the cavity is packed like an overstuffed chair, and in places the fabric bulged so much the sheetrockers complained that it was hard to attach the board. In the case of blown in, it seems prudent to get sheetrock on it as fast as possible as it doesn't appear to stick in the cavities all that well, especially in the presence of all the pounding that goes on during construction.
|Insulation sprayed onto walls and blown into ceiling (far left), in this case just as a sound barrier between the two units. Although the insulation didn't stick well in our deep walls cavities (right), its stuck just fine in the 2x4 walls. Still it doesn't take much to knock it out, so you have to cover it with sheetrock pretty quickly. In the blown in system, fabric is stapled to the studs, and the cellulose is blown into holes punched into the fabric (center).|
If there is any obvious downside to cellulose, it is that it is terribly dusty, and the dust seemed noxious. The installers wore masks and as we were making last minute changes to framing and electrical, we quickly discovered that the dust is really irritating to your lungs and eyes. Even with a mask, you need to go to fresh air frequently to keep your eyes from getting too irritated. Like sheetrock, once installed, cellulose is best left alone. Of course it is easy to argue that fiberglass is just as bad, if not worse.
There are a few situations where we used foam board to supplement the cellulose: there were three cases where we had framing that wasn't thick enough to hold the amount of insulation we wanted to we added foam board to the exterior. (TBA details when we actually do this.). We also plan on using a polystyrene board to insulate the sauna, since cellulose won't tolerate the high temperatures of the sauna, and having lost her father to asbestosis, Kim wanted no part of fiberglass, even if in reality the health risks don't compare. It was more an issue of why take any risk at all when an alternative is available.
Since the roof is an SIP, the insulation is also the structure, and in this case the insulation material is polystyrene.
We seal of as many possible air leaks not only to reduce our heat loss, but to keep moisture laden air out of our insulation. The outside of the house is covered in an overlapped double layer of tar paper (see siding for more details) to slow wind penetration, and all penetrations in the envelope as sealed with spray foam. This includes sealing around all plumbing plumbing lines, electrical lines and ventilation ducts that travel through an insulated cavity. Because plywood is part of our air barrier, we also seal any joints between plywood that you can see daylight through, and likewise in all the rim joists. Because plywood is more very permeable to water vapor, the downside to our air sealing is that it reduces the ability of the wall cavity to dry to the exterior. At this time, we know no good solution to this.
We used two different products for air sealing: a low expansion foam was used for most of the locations (they call it non-expanding, but in fact it expands so you have to be careful in places like around door jambs), and a non-hardening foam/caulk made by DAP, which was used around the windows. The sun tube (pictured below) was sealed with a third product in a demonstration of a new two part foam product.
Various Air sealing locations
Sun pipes are notoriously leaky, so we sealed ours real well with a new kind of spray foam (far left). The rim joists in the basement are sealed (2nd from left), and so are the wires & pipes coming up from the basement (2nd from right). All around the windows, we use a non-hardening caulk (far right).