It feels that the focus in green building is on new homes being built to Passive House standards or the like. There’s a lot to be learned there, but it’s top-of-the-pyramid stuff. Most builders don’t work at that level. Certainly, most of the work my partner and I do isn’t there. We work largely on old buildings. Faced with the realities of time and budget, we do what we can.
We just had a job spray-foamed. It was an old barn with irregularly spaced framing. Most other kinds of insulation would have been a lot more difficult. We stapled housewrap to the back of the siding and the edges of the timber frame. In doing so, we worked from the top down in a mirror image of how you’d install housewrap from the outside. That created the necessary shingle-style lap on the outer face of the housewrap. The housewrap kept the foam from oozing out through the cracks in the old vertical siding, made replacing pieces of siding down the road a lot easier, and made the insulation of this circa-1795 barn reversible.
We were only able to get 3 in. to 4 in. of closed-cell foam in the walls, but at R-6 per in., that meant a solid R-18 to R-24, plus air-sealing. The contractor used one of the new blowing agents with a global warming potential equivalent to CO2, so the carbon debt of the insulation will be repaid quickly.
Just what are the nuances?
Still, compared to what we know is possible, our wall insulation is anemic for zone 5. In an effort to find out just which level of green-building Hell we are destined for, I began to wonder just how much of a difference relatively minor amounts of insulation make. This thinking…