How To Put Plywood Flooring In An Attic (Over Insulation)

Many people like using their home’s attic to provide a little extra storage space in their homes. Aviation-grade plywood is manufactured to a number of specifications including those outlined since 1931 in the Germanischer Lloyd Rules for Surveying and Testing of Plywood for Aircraft and MIL-P-607, the latter of which calls for shear testing after immersion in boiling water for three hours to verify the adhesive qualities between the plies and meets specifications.

I replaced the slab when I bought the house so I know there is a vapor barrier and about 2ft of base rock under it. Our geography is such that the shop is high side of the structure on a gentle slope (the 1st floor of the house is actually the 2nd floor and there no exterior ground contact except for the carriage doors at the entrance) and our climate is pretty mild so not a lot of moisture and temps rarely get to the mid 30s in winter.

When you throw in the partition walls, all of the subflooring, the tile underlayment, the mortar, the fasteners, the tile, the toilet, the shower, the vanity, the heavy granite countertop…it all adds up. Then, in your fancy homes you like to work on, throw in a 100# chandelier hanging from that floor below and a real plaster ceiling, and your dead load margin goes down even quicker.

Even though you may think your homes environment is dry, interior relative humidity moisture levels and ground water tables can change frequently from month to month, We recommend laying 15 lb. black felt Hardwood flooring underlayment paper over the wood subfloor overlapping the seams 4-6 inches to help retard moisture transfer that may migrate up from damp basements through the subfloor and affect the stability of the Hardwood floor.

During the manufacturing process, plywood veneers are randomly selected and stacked up into panels. Debris left on the subfloor can cause problems with the underlayment down the road. A dead load in excess of the design means the floor doesn’t rebound, and takes a set. Plywood and OSB subfloors over joists are most common in newer homes and new construction, typically in homes with basements or crawlspaces. Each sheet of plywood is 32 sqft (4×8 = 32) … so we divided 1500 by 32 and got roughly 47 sheets. Subfloor thickness can also depend on what type of flooring you are putting down.