After pouring the concrete to form the foundation wall of the home, a damp proofing and waterproofing process is used to keep water from entering the basement. However, concrete can hold water for a long time and in cold climates, the ground can freeze, radiating the cold inside the home. In order to stop this, you must insulate the basement walls.

Step 1: A two-inch solid rigid foam closed cell insulation acts as a water barrier from both directions. Closed-cell foam insulation does not absorb water. If potential for flooding exists or ground water is present, use this type of insulation. The R-value depends on your climate zone. You can typically use the R-value that is recommended for upstairs walls. The number decreases as you go down further into the ground because the outside temperature of the ground usually increases.

If water vapors form inside the basement and attempt to touch the concrete foundation wall, they will be blocked by the insulation. If this insulation was not present, the vapors could condense, creating an environment for mold and mildew to grow. If the concrete has water in it, the insulation can keep the water from entering the basement.

Step 2: When installing the insulation, cut the piece to span the full height of the wall from the slab up to the top of the concrete. The top of the wall and the sill area are coldest and this is where most leaks occur.

Step 3: The insulation has tongue and groove edges that interlock to create a seal. Where two pieces of insulation meet, you must tape the seam with a special tape made by the insulation manufacturer. This tape sticks to the foam for the life span of the building.

Step 4: Build the 2×4 wall tight against the rigid foam closed cell insulation. Fiberglass insulation should then be installed against this for additional protection.

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