How to Insulate Your Basement Floor

Rigid foam insulation

Similar to insulating the walls of your basement, insulating the floors requires framing work to provide the proper home for the insulation. The type of framing required is as easy as it gets, so don't discount yourself too quickly from being able to do this project. You will gain a more comfortable home environment, a mold free basement and savings on your yearly energy bills.

Things You'll Need

• 2x4 pressure treated studs
• 1-1/2" rigid foam insulation
• 2" galvanized wood screws
• 3" masonry screws
• 3/4" tongue and groove subflooring

Instructions

1. Verify your basement floor does not have a legitimate water infiltration problem. If your concrete floor has any kind of standing water during the winter months, then insulating the floor is going to be a waste of money. The water will ruin the insulation and wood framing around it. Address this problem first.

2. The concrete floor slab needs to be sealed before any other step is taken. Purchase a heavy duty concrete sealer. There are many brands out there. Go to your home improvement center and get advice on the products that they carry. Since this concrete will be covered with framing and insulation after you seal it, you only have one chance to get it done right. Spend some extra money to get the best product.

3. 

   Clean the concrete floor thoroughly, eliminating all dust and debris, and then apply the concrete sealer. Typically, this application will be rolled on with a painter's roller. I recommend applying two coats. Wait at least 24 hours between coats or as recommended per the manufacturers instructions.

4. 

   Build the raised floor. Since all of the framing will be installed directly on top of the concrete, it will have to be pressure treated lumber otherwise the wood can still rot out over time despite the protective concrete sealer you applied to the floor. Lay down 2x4's with the flat side down on top of the concrete, they are called sleepers when you do this. Install them around the entire perimeter and fasten them into the floor with 3" masonry screws every couple of feet. Next lay down 2x4 sleepers every 16" on center that span from wall to wall; run them all in the same direction. The final product will look like a nice grid. Toe nail the ends of the sleepers into the rim pieces previously installed. Add blocking every three feet between the sleepers in the opposite direction that the sleeper are run.

5. 

   Install Owens Corning, or better, 1-1/2" rigid foam insulation in the bays between the sleepers. Rigid foam insulation is resilient against the natural dampness present in concrete. Rigid foam insulation comes in 15" and 23" wide boards. Since you framed at 16" on center, buy the 15" wide boards. Use a utility knife to cut the boards to the proper length.

6. Install 3/4" tongue and groove plywood on top of the sleepers. Screw the plywood into the sleepers every 8" on center using galvanized or stainless steel 2" wood screws. You cannot use regular steel or aluminum fasteners with pressure treated wood, they will dissolve over time in due to the chemicals in the wood.