Hardwood Floors April/May 2017

When using plywood subfloors, the following should be considered: • Plywood thickness varies and will be determined by joist type, span, and anticipated load. • Plywood has good moisture resistance and quicker acclimation times than OSB. • Plywood is typically more expensive than OSB. • Plywood requires 1/8” spacing between all panels, on all four sides. DOUBLE LAYER SUBFLOORS When a second layer of subfloor material is necessary to meet the minimum subfloor panel requirement: • The second layer must be minimum 15/32”. • The top layer should be offset by 1/2 panels in each direction to the existing subflooring, with no seams falling in the same space. • The top layer also may be installed on a diagonal. • The panels must have 1/8” spacing between sheets and must have 3/4” perimeter expansion at all vertical obstructions. • Before installing, allow both panels to acclimate to the area in which they will be installed. • The second layer of panels should be installed with fasteners (ring or screw shanked nails or equivalent) only to the subfloor panel and not the floor joists, and at 6” on center along all panel edges and an 8” on center grid through the field of the panel. INSTALLATION OVER EXISTING FLOORS When installing over solid board subflooring or existing wood floors, consider: • If safe, sand off the old finish and/or any high spots, to properly flatten the substrate. • Prep the existing floor to be clean, dry, sound and flat. • Repair, re-nail or replace loose flooring in the existing floor. • Ensure that the moisture content of the existing floor and the new wood flooring are compatible. • Solid board subflooring is 3/4” x 5 1/2” (1” x 6” nominal), Group 1 dense softwoods. These subfloors should be installed at a 45-degree angle to the joists. • Wood flooring should always run perpendicular to the floor joists or on the opposite diagonal to the subflooring. • Some engineered flooring, parquet, and thin classification solid flooring may not be recommended over these subfloors without additional underlayment. • Installing over an existing wood floor is also possible, but different scenarios call for different methods. Follow the flooring manufacturer recommendations when available.

the magazine of the national wood flooring association

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