Q&A: A Forum for Green Building Experts and Beginners

Hello! This summer we are building a greenhouse addition with an underground root cellar attached. In one of the root cellar books I read, they recommend Everdure Caltite as an additive in concrete to make the foundation waterproof. What are your recommendations?

I have insulated my basement slab with 1" expanded foam board with floating 3/4" T&G OSB biscuit joined on the ends according to the Mixed Humid Builders Guide. The walls have 2" expanded foam board. Expanded foam was chosen to allow drying to the interior. 6 months later the subfloor started cupping at the seams. Afterwards I figured out that a vapor barrier wasn't installed under the slab when the house was built, which would explain my problems.

I have been thinking about my options and have come up with 2 that I think will work.

Zone 4 marine. I'm pondering insulation strategies for cathedral ceilings.

In the past we have used typical cardboard baffles and either batts or blown in FG. Recently we did a small project where we cut and fit 2" polyiso for the baffles, with the usual 1" vent space above and foamed the edges, my theory being that this will reduce wind-washing of the fiber insulation and improve air-leakage performance. We also did one with 6" of solid polyiso where there was only 2x8 rafter space available.

So I'm a bit confused here. My understanding of urethane foams (e.g. closed cell spray foam or polyiso) is that the blowing agent gases trapped within the closed cell structure slowly leak out over time and is replaced with air, depreciating the R-value. But then I see that certain companies advertise that their polyurethane spray foam products/kits do not off-gas. Is the leakage of the blowing agent not off-gassing, or is the manufacturer making a false claim? I'm assuming that they use an HFC blowing agent. Maybe I'm just missing something.