4 / RECOMMENDED SUBFLOOR SURFACES CONCRETE SUBFLOORS Concrete slabs should be of high compressive strength (Minimum 3000 psi) and constructed to prevent groundwater from permeating the concrete. Engineered hardwood flooring can be installed on, above, or below grade. In addition, it can be installed over above-ground, suspended concrete floors. The suspended concrete must be a minimum of 1 ½ inches thick and must be structurally sound. The exception to this is lightweight concrete (which usually contains high amounts of gypsum) having a density of 100 pounds or less per cubic foot. Test for lightweight concrete by using a nail to scratch the surface of the concrete. If the concrete crumbles or turns to powder, it is not sound and you should NOT install hardwood flooring. WOOD SUBFLOORS Subfloor panels should conform to U.S. Voluntary Product Standard PS1-07, Construction and Industrial Plywood and/ or US Voluntary PS 2-04 and/or Canadian performance standard CAN/CSA 0325.0-92 Construction Sheathing. Other CSA standards also apply. ACCEPTABLE PANEL SUBFLOORS: TRUSS/JOIST SPACING WILL DETERMINE THE MINIMUM ACCEPTABLE THICKNESS OF THE PANEL SUBFLOORING. • On truss/joist spacing of 16” o/c or less the industry standard for single panel subflooring is minimum 5/8” 19/32”, 15.1 mm) CD Exposure 1 subfloor panels, 4x8 sheets. • On truss/joist spacing of more than 16”, up to 19.2” (488mm) o/c, the standard is nominal ¾” (23/32”, 18.3 mm) T&G CD Exposure 1 Plywood subfloor panels, (Exposure 1) or nominal ¾” 23/32”, (18.3mm) OSB Exposure 1 subfloor panels, 4’x8’ sheets, glued and mechanically fastened. • Truss/joist systems spaced over more than 19.2” (488mm) o/c up to a maximum of 24” (610mm) require minimum 7/8” T&G CD Exposure 1 Plywood subfloor panels, (Exposure 1), or minimum 7/8” OSB Exposure 1 subfloor panels, 4’x8’ sheets glued and mechanically fastened – or two layers of subflooring or brace between the truss/joist in accordance with the truss/joist manufacturer’s recommendations and with local building codes. Some truss/joist systems cannot be cross-braced and still maintain stability. • For existing wood floors install new flooring at right angles to the existing flooring. • Do not install over particle board, existing glue down or floating hardwood floors. CORK/ACOUSTIC UNDERLAYMENT: (GLUE DOWN ONLY) Install the cork/acoustic underlayment according to the manufacturer’s instructions. The cork/acoustic underlayment must be fully adhered to the subfloor. Cork underlayment should be of pure granulated cork combined with a polyurethane binder with a minimum density of 11.4 lbs. per cubic foot and not to exceed 13 lbs. per cubic foot. 5 NWP INSTALL GUIDE RECOMMENDED SUBFLOOR SURFACES
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