COLUMN BUILDING SCIENCES FIGURE 3 Basement foundation environmental separation. FIGURE 4 Crawlspace foundation environmental separation. environmental separation aspects of crawlspace foundations. The crawlspace illustrated in Figure 4 is a vented 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 the continuous rigid insulation installed under the floor joists. The continuous rigid insulation under the floor joists is acting as the air control layer of the insulated floor assembly. 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 impermeable continuous rigid insulation under the floor joists. Additionally, a continuous polyethylene ground cover is provided. Thermal control is provided by installing continuous exterior insulation and cavity insulation on and in the wall framing. Additionally, continuous rigid insulation under the floor joists. This approach works in all climates. Crawlspace Foundation With A " Cripple Wall " Figure 5 illustrates the environmental separation aspects of crawlspaces with " cripple walls. " The crawlspace illustrated in Figure 5 is a vented 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. For stucco claddings it is recommended that two layers of building paper be used. The outer layer of the building paper acts as a " bond break " to facilitate drainage. The bottom of the stucco assembly should have a " weep screed " that acts as a flashing. The air control layer of the exterior wall is typically building paper. The air control layer of the underside of the floor framing is continuous rigid insulation. This rigid insulation should be fire rated with joints taped and sealed. It is sealed to the interior of the perimeter " cripple " wall framing. The rigid insulation is also protected from animals, rodents and insects with protection board. Vapor control is provided by installing foil faced rigid insulation on the underside of the floor framing. Additional vapor control is provided by installing a continuous polyethylene ground cover that is connected to the interior of the concrete foundation stem wall and by providing crawlspace ventilation. Crawlspace ventilation should have a minimum net area ventilation opening of 1 ft2 (0.1 m2) for each 1,500 ft2 54 ASHRAE JOURNAL ashrae.o rg S E PTEM B E R 2022https://ashrae.org/