Should you waterproof a slab foundation?

Foundation waterproofing for above-grade slab foundations is not only beneficial for keeping water out of the house. It will also go a long way in protecting mechanical systems. These mechanical systems are installed in the base before gravel and concrete are poured into the base. Most waterproofing systems need protection during backfilling.

Some manufacturers have their own protective plate for this purpose. A drainage or insulation mat can also function as a protective board. An inexpensive 1-inch thick expanded polystyrene foam board works well as a basic protective layer. However, a manufacturer has a protection plate that functions as insulation, protection plate, and drain medium in one.

There's really no reason to have a shoe drain or moisture protection with slab above grade. If you have a groundwater problem (which you say no), a case could be made to keep water out of the EPS insulation, as it could affect the R value. You should have a good vapor retarder under the slab. If the foundation wall is blocked, a good large layer or equivalent will protect it from prolonged freeze-thaw damage.

If you're using a waterproofing subcontractor, recognize that good waterproofing materials can be in high demand during peak season. Another waterproofing agent once told me that in one of his jobs the general contractor sent a worker, after applying the waterproofing, to break the ties of form inside a foundation.

Gwenda Hunt
Gwenda Hunt

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