Recommendations for Subfloors

Those areas of the country that use 5/16" top nailed oak flooring should have at least 3/4" of subfloor, or more ideally 7/8" of subflooring.  The nails used to fasten 5/16" oak to the sub-floor are 1" long.  These nails are driven vertically and are countersunk into the top flooring.  To contain the entire length of the nail and avoid splitting the subfloor or splintering it at the bottom; the overall thickness should be 1 1/8" minimum, including the 5/16" top floor.  The 7/8" subfloor would also add structural strength  to the floor and avoid diaphragm or "diving board" action in the hundred of thousand of square feet of 5/16" glued down parquets.


Click on Image to see Larger


The method we suggest for "on grade" slabs and sometimes on suspended slabs is as follows:


Click on Image to see LargerTwo plies of 15 pound asphalt saturated felt, each set in a bed of asphalt adhesive with the edges butted and the end joints offset and turned up the wall to the height of the finished floor.  The second layer lapping the first layer by a half sheet, to form a sealed vapor barrier.

Apply a third layer of asphalt adhesive using an 1/8" notched trowel, over the membrane.  Cut 1/2" plywood, (not particle board) in 2' x 4' sheets; and install in adhesive at a 45 degree angle to the wall line.  Overlay the 2' x 4' pieces of plywood with full sheets on 1/2" plywood, crisscrossing the first layer.Click on Image to see Larger

Staple the two layers of plywood together with 7/8" divergent point stapes 12" on center.

The slab should be clean, flat and dry before job is started.

This will provide a subfloor that will accept top nailed strip or plant, T & G strip of plank, and any glued down parquet and provide a strong, moisture resistant, versatile subfloor.

For additional information see installation manual and the Finishing/Refinishing manual issued by the National Oak Flooring Manufacturing Association.