Sub-Flooring

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Sub-flooring and Sheathing
Plywood - Plywood sub-flooring is the most popular product used today.  The material is often installed with a construction adhesive on the floor joists and is nailed or screwed. Quite often, the nailing is inadequate, resulting in squeaking floors.  Almost all plywood sub-flooring in residential construction is 3/4 inch thick. When ceramic tile is planned, an additional 1/2 inch of plywood should be installed over the 3/4-inch plywood.  One concern is the additional 1/2 inch of height it adds to the floor.  There should also be consideration given to strengthening the floor (i.e. installing the joists with closer centers, or deeper joists).

Hardboard - Hardboard is the term used for pressed board, such as Masonite.  It is typically used as underlayerment to receive vinyl sheet goods and resilient tile.  It is not as stable as plywood.  The nailing pattern for hardboard underlayerments should be 6 inches or less. 

Oriented strand board (OSB) - OSB is a structural grade wood product that generally has the same uses as plywood for a little less money.  It looks like wood chips and thin pieces of wood that are glued and pressed together.  It comes in interior and exterior grades.  The most common sheet sizes are 4 x 8 x 1/2 inch or 3/4 inch thick.

Flake-board – Flake-board is sawdust mixed with glue resins and formed into 4 x 8 sheets. In the presence of water, this material will delaminate, which limits its usage.  These boards are very dense and are heavier than plywood or OSB, which also limits its usage.

3/4-inch T&G pine - T&G boards are used as sub-flooring, roof and wall sheathing.  It is found in homes built in the 1920s, 30s and 40s, and very often with 3/4-inch hardwood flooring nailed over top.  Plywood replaced 3/4-inch T&G as sheathing and sub-flooring.

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