COLUMN BUILDING SCIENCES FIGURE 5 Crawlspace foundation with " cripple wall " environmental separation for a vented crawlspace. FIGURE 6 Crawlspace foundation with " cripple wall " environmental separation for an unvented conditioned crawlspace. (139 m2) of under floor area space when a Class I vapor retarder is used as a ground cover. The continuous polyethylene ground cover is a Class I vapor retarder. Additionally, the required crawlspace ventilation openings should be placed to provide cross ventilation of the space. It is recommended that at least four ventilation openings be located around the perimeter of the building. Ventilation openings should not be located under low decks or porches. If a Class I vapor retarder ground cover is not installed, the net ventilation opening area needs to be increased to a minimum of 1 ft2 (0.1 m2) for each 150 ft2 (13.9 m2) of under floor area. Note that the number of openings and vent area needs to be increased by an order of magnitude and this can adversely affect the ability of the " cripple " wall to resist seismic activity. Thermal control is provided by installing continuous rigid insulation and cavity insulation on the underside of the floor framing. This approach works in all climates. Figure 6 illustrates the environmental separation aspects of crawlspace foundations also with " cripple walls. " The crawlspace illustrated in Figure 6 is an 56 ASHRAE JOURNAL ashrae.o rg S E PTEM B E R 2022 unvented conditioned crawlspace. A continuous water control layer controlling rainwater is installed on the exterior of the wall structural sheathing and is connected to the continuous water control layer on the exterior of the concrete foundation stem wall. A continuous air control layer is installed on the exterior of the wall structural sheathing and is connected to the top of the concrete foundation stem and in turn to a continuous polyethylene ground cover that is extended up the interior of the concrete foundation stem wall. Figure 7 illustrates continuity of the air control layer at interior posts and piers. Vapor control is provided by controlling the temperature of the wall assembly condensing surface by installing continuous exterior insulation. Vapor control of the crawlspace foundation is provided by installing a continuous polyethylene ground cover that is extended up the interior of the concrete foundation stem wall. Thermal control is provided by installing continuous exterior insulation and cavity insulation on and in the wall framing. Additionally, foil faced or plastic faced batt/roll insulation is installed on the interior of the concrete foundation stem wall extending horizontally over the polyethylene ground cover. This approach works in all climates with the followinghttps://ashrae.org/