COLUMN BUILDING SCIENCES FIGURE 9 Crawlspace Perimeter. It is necessary to connecting the underside of the FIGURE 10 More Crawlspace Perimeter. Being the nervous conservative old guy crawlspace floor framing through the perimeter rim joist area to the exterior wall assemblies in an airtight manner. I have become I worry about critters getting into the rigid insulation and pretty much always recommend some type of protection board over the underside of the rigid insulation. Fibercement boards work well in this regard. best choice is to go the mini-basement approach. But maybe you can't construct a conditioned crawlspace. Hey, maybe you need to construct a vented crawlspace because you are in a flood zone or you live over a swamp (like most of the state of Florida or the fun parts of Louisiana). Vented crawlspaces become worse when impermeable floor finishes are used such a vinyl flooring as pointed out earlier. Can we safely and reliably install wood flooring and vinyl flooring over plywood and OSB subflooring over vented crawlspaces? Yes. We just need to keep the air and vapor out of the crawlspace floor framing. Check out Figures 7 and 8. Both show foil-faced rigid insulation under the floor framing. The wood is warm and therefore dry during both winter and summer. The foil facing on the rigid insulation handles the vapor drive. The foil facing is an exceptional vapor barrier (<0.1 perm). Beautiful. With the impermeable rigid insulation even relatively impermeable floor coverings such as vinyl flooring work. So why don't we see lots of this? Well, I forgot to mention that the rigid insulation needs to be airtight so that requires good workmanship to seal the seams with foil tape that sticks in miserable environmental conditions forever. Having said that, a poor job using the approaches described in Figures 7 and 8 are way better than what we typically get with Photo 2. Figures 9 and 10 show the perimeter details, connecting the underside of the crawlspace floor framing through the perimeter rim joist area to the exterior wall assemblies. Being the nervous conservative old guy I have become, I worry about critters getting into the rigid insulation and pretty much always recommend some type of protection board over the underside of the rigid insulation. Fibercement boards work well in this regard (Figure 10). JAN UARY 2020 ashrae.org ASHRAE JOURNAL 69http://www.ashrae.org