COLUMN BUILDING SCIENCES FIGURE 1 SIPS wall assembly. Prefabricated building panels consisting of plastic foam cores sandwiched between two skins, typically oriented strand board (OSB) or plywood. Foam sealant FIGURE 2 Roof panel airflow problems. It is necessary to control airflow from the interior to the exterior at panel joints, particularly at roof assemblies. Area prone to moisture damage Movement of air and moisture in panel joint toward roof peak SIP Open joint Spline cuts in foam Foam recessed for top plate Top plate PHOTO 1 Bad stuff happens at ridges- " ridge rot. " Wall panel Wall panel FIGURE 3 Telegraphing of panel joints. Telegraphing can occur due to panel movement. Telegraphing can also occur due to localized increase in moisture content. Upper surface has a greater moisture content than lower surface when Cold Side Bottom plate Foam recessed for bottom plate Spline installed in field (front and back) PHOTO 2 Telegraphing of panel joints in roof assemblies under asphalt shingles. Warm Side When upper surface expands relative to lower surface panels can bow; at a minimum, upper joints close-or deform by crushing- as upper surface expands Initial distance between nails Distance between nails closes as moisture content of upper surface increases Gap closes Initial gap between panels to the interior (Figure 4). Yup, two locations-belt and suspenders-systems redundancy. This is a really, really big deal in roof assemblies. What else? The ridge-the ridge. Did I mention the ridge? See Figure 5. Note that there are three options. Pick one. Shingle stressed between nail leading to telegraphing of joint Localized increase in moisture content can occur due to air leakage through joint or via vapor diffusion through joint where vapor diffusion source is wood timber at high initial moisture content Wood timber at high initial moisture content O CTO B E R 2 0 2 4 ashrae.org ASHRAE JOURNAL 19 upper surface is cold and lower surface is warmhttp://www.ashrae.org