COLUMN BUILDING SCIENCES FIGURE 5 Venting House Through Crawlspace. You can vent the house through the crawlspace, exhaust only ventilation with makeup air supplied to the crawlspace from the house. This is a variation of exhaust-only house ventilation. FIGURE 6 Radon/Soil Gas Vent. Radon and other soil gases need to be addressed with conditioned crawlspaces just as they need to be addressed in basements. The best approach is the typical sub slab, sub poly "radon vent." FIGURE 7 (LEFT) Vapor Barrier. Installing impermeable rigid insulation keeps the wood framing warm and provides a low perm layer that addresses the upward vapor drive. How impermeable? Less than 0.1 perms. Foil faced rigid insulations are the ticket here. This approach allows any type of flooring to be used above. The rigid insulation also needs to be airtight. FIGURE 8 (RIGHT) Cavity Insulation with Vapor Barrier. Adding impermeable foil faced insulating sheathing over fiberglass cavity insulation is a hybrid approach that uses the best qualities of both materials. Note that the optimum location for the airspace is above the cavity insulation. Makes for warmer floors; this is the same detail that should be used under bedrooms over garages. Note that the rigid insulation also needs to be airtight. dehumidifier. The dehumidifier handles the moisture control.# What about radon and other soil gases? Yes, they need to be also addressed. The best approach is the typical sub slab: sub poly "radon vent" (Figure 6). #We 68 Now for the not so obvious one. It should be obvious, but it is not. How do you construct a vented crawlspace without causing moisture problems? Here is where I point out that conditioned crawlspaces are more energy efficient than vented crawlspaces, and your first condition unvented attics with dehumidifiers all the time. It works pretty much the same way with crawlspaces. ASHRAE JOURNAL ashrae.org JAN UARY 2020https://www.ashrae.org/