A basement floor doesn’t have to be cold and damp. In fact it shouldn’t be if your builder did the job right when your home was constructed. Many older homes were built correctly; they just didn’t know or have the modern building materials that we have today. If you’re remodeling your basement and starting from scratch with a new slab, then you need to know basement floor insulation basics before you begin!
Since most basement floors are built in direct contact with the ground, they tend to get damp and cold from the ground below. Mold, mildew and general dampness is a common condition with concrete basement floors. Heat is also lost through the floor. Trying to heat a basement with a conventional uninsulated concrete floor is an almost impossible task and certainly a waste of energy.
Creating an insulation layer and a vapor barrier between the concrete slab and the ground is the only solution to a dry and warm basement floor. This will keep the warm air in and keep the wet moisture out.
Once you’ve removed the old concrete floor and you’re down to bare earth, you’ll need to spread a layer of base gravel onto the soil. This should be about 4″ thick but the more the better. Don’t forget to remove the extra soil for the extra gravel or your slab is going to be higher than the last one.
Now that a layer of evenly spread base gravel is set for drainage, you can begin the insulation process. Sheets of polystyrene foam typically come in 4×8 panels of varying thickness. Of course the thicker the foam, the better the insulation, but it can get costly. One inch thick foam works just fine.
Tape the joints together using foam tape or duct tape. Don’t leave a single air gap or space between foam panels and ensure they are all tightly sealed before adding the vapor barrier.
Now cut to fit a 5mil or greater polyethylene vapor barrier onto the foam panels. Cut the largest piece possible. The less seams, the better the vapor barrier will work. Tape all of the joints with builders tape. A layer of caulk between plastic sheets followed by tape is the best seal you can get.
All that is left is to pour the concrete over the vapor barrier and finish for the perfect insulated basement slab.