COLUMN BUILDING SCIENCES of airborne embers/cinders. These screens also serve a second function-the control of entry of insects and pests into the drainage and ventilation gap. Here is a big thought, have your vent space as small as possible. Keep the vent space ¾ inch (19 mm) or less to limit fire propagation. Bigger is not better. The main objective to limiting fire spread is to slow air (oxygen) from feeding a fire. Where gaps are ¾ inch (19 mm) or less the fire risk is minimal due to boundary layer friction of the two surfaces. Fire within cladding assemblies where air gaps are small is starved for oxygen. Synthetic stucco assemblies such as exterior insulated foam systems (EIFS) pose a small fire risk as there is no gap between the thin exterior lamina and the extruded polystyrene (EPS) the lamina is adhered/bonded to even though EPS is combustible. Drainage is provided behind the EPS by the gap resulting from installing vertical beads of adhesive that attach the foam to the water control layer. FIGURE 4 Building section showing a vapor diffusion ridge port constructed with fire resistant and fire retardant materials. This gap is approximately 1/8 inch (3.1 mm). You can get drainage in gaps as small as 1/32 inch (0.8 mm). The key is to make this gap continuous. High Performance. Narrow Profile. For exceptional efficiency in a narrower profile, Ruskin® DC-series dampers feature high-performance airfoil blades, a Class 1A leakage rating* and an all-new coupler option that joins two damper sections without a jackshaft. *AMCA Class 1A leakage is defined as 3 cfm @ 1-in.wg. ruskin.com 34 ASHRAE JOURNAL ashrae.org A U G U S T 2 0 2 1http://www.ruskin.com http://www.ashrae.org