Building a subfloor on a concrete slab

Building a subfloor on a concrete slab is the first step in finishing a basement. The subfloor will not only provide a level base, but, since the floor won't be as cold or as hard on the feet, it will also be more comfortable. Before getting started, make sure that there is no water infiltration on the basement concrete slab.
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1. Taking measurements
2. Laying 15 lb. felt paper
3. Framing the subfloor
4. Leveling and nailing down the sleepers
5. Screwing down the plywood sheets

1. Taking measurements

Draw a plan of the floor area on a sheet of graph paper, using one square per square foot of floor. Determine the number and length of 2 in. × 3 in. pieces required for the perimeter of the basement. Next, determine the number and length of 2 in. × 3 in. pieces required for the sleepers that will be nailed on 40 cm (16 in.) centres. Finally, determine the number of 4 ft. × 8 ft. plywood sheets required for the subfloor.

2. Laying 15 lb. felt paper

Lay 15 lb. felt paper directly over the concrete slab to block any infiltration of humidity from the ground. To ensure better waterproofing, leave an excess of approximately 10 cm (4 in.) of felt paper along each basement wall.

Instead of felt paper, you can also use a 6 mil polyethylene sheet.
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