How to install a plywood subfloor on a concrete slab

Written by j. cavan barry
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How to install a plywood subfloor on a concrete slab
Plywood sheets cover the floor faster than planks. (Thinkstock/Stockbyte/Getty Images)

Concrete is one of the most commonly used building materials for homes today. Some flooring materials, most commonly hardwood floors, require the application of a plywood subfloor prior to flooring installation. Plywood is an easy material to fasten flooring material to, and also offers an expansion and contraction (due to temperature and moisture changes) buffer between the concrete slab and the flooring material. The application of plywood subflooring is usually an easy task that just about anyone with basic construction tools can complete.

Skill level:

Things you need

  • 6 mm (1/4 inch)polythene vapour barrier
  • Tape measure
  • Razor knife
  • OSB plywood
  • Concrete nail gun with concrete nails
  • Circular saw with carbide wood blade
  • Lumber pencil
  • Chalk line

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  1. 1

    Spread a polythene vapour barrier over the concrete floor from wall to wall, leaving about 10 cm (4 inches) of extra material up the wall; you can use a razor knife to cut the plastic. This polythene vapour barrier keeps any moisture from transferring from the concrete to the wood, thus preventing mould and mildew.

  2. 2

    Lay a sheet of plywood 1.6 or 1.9 cm (5/8 or 3/4 inch) thick plywood is most commonly used) on the concrete floor (over the vapour barrier) against a wall corner, and use a concrete nail gun to drive concrete nails through the wood and into the concrete floor at 40 cm (16 inches) on centre.

  3. 3

    Lay the next sheet of plywood at the long end of the first sheet set in Step 2, and fasten to the floor using concrete nails. Continue this to the opposite wall, cutting the last sheet of plywood (if necessary) using the circular saw with a carbide wood blade.

  4. 4

    Cut a sheet of plywood in half lengthwise at 1.2 or 1.5 m (4 or 5 feet) depending on the full sheet size, to lay as the first sheet for the next row, next to the first sheet set in Step 2. Repeat Steps 1 through 3 to complete this row and following rows until you cover the entire floor with plywood subflooring.

  5. 5

    Repeat Steps 1 through 4 in remaining rooms; you can use a small strip of plywood to place on the floor under doors.

Tips and warnings

  • Refer to the flooring material specifications you're going to use to determine the thickness of plywood subflooring you require.
  • To ensure a straight cut, you can measure and snap a reference cut line on the plywood using a pencil and chalk line; measure and mark two sides of the plywood, and connect with the chalk line.

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