We're shooting for the Passive House Standard on this project, which means one of the big targets is that it's got to be really air-tight. Below 0.6 ach50, to be precise. Since this is the first time we're attempting this, we're testing a few different strategies. One of the materials we're using is closed-cell spray foam. Here we're spraying it between the floor beams and the crawl space to completely fill the gap between the rim joist and our nicely insulated stem walls. The idea is that the spray foam insulation will create both an effective continuous thermal barrier and will also seal any gaps we have in our building envelope. Keeping our crawl space well sealed from the outside will also ensure that no contaminated air, earth gases or mold spores will infiltrate into the living space.