Whether you are living in an existing home or building a new one, everyone wants a dry basement. In fact, questions about water problems in basements—in both new and existing homes—are some of the most common I’ve been asked.
Let’s take a look at both of these separately as the approach will be different, but first, let’s discuss what they should have in common.
Regardless of your home’s age, the grade of your yard should pitch away from your house about 5 to 6 inches in 10 feet. Sidewalks, patios, and driveways should also slightly slope away from your home to divert any surface water away from the foundation. Any expansion joints or cracks should be caulked with an approved flexible urethane sealant to stop any water seepage. Gutters and downspouts with extensions (at least 5 feet) will carry rain water from the roof away from the building. The water from any adjacent properties should enter a curtain drain or a swell directing the water away from your home.
Dampproofing vs. Waterproofing
Dampproofing is an asphalt-based coating that is applied to the outside of the foundation wall either by hand brushing or spraying before backfilling. Dampproofing is used frequently on foundations to stop moisture at the surface of the wall from penetrating when there is good drainage at the foundation wall from granular soil conditions and/or drain tile that will eliminate hydrostatic pressure that forces water into the foundation wall. This makes dampproofing adequate protection for basements and crawl spaces.
Waterproofing, on the other hand, is a system that uses a combination of coatings and plastic membranes on the exterior foundation walls. This system is used when conditions have poor drainage or a high water table that creates hydrostatic pressure at the wall surface. A foundation with large cracks will also use this system. Although it is more expensive, it can be a better alternative when conditions are in question.
Once the foundation is poured, the forms are stripped
, when the concrete is partly cured, the wall ties are removed, the walls are inspected for any cracks, and the top of the footings are cleaned off. Dampproofing is then sprayed or brushed on the exterior foundation wall and on top of the footing. Perforated drain tile is then installed at the perimeter of the foundation alongside the footing. Washed stone or course gravel is used to completely cover the tile on the top and side (gravel size larger than the holes in the tile). Filter fabric is then installed to cover the stone before backfill. Sand or similar backfill can help keep fabric clean when backfilling. Sometimes drain tile should also be installed inside the foundation under the basement floor slab at the footing if ground water exists. Vapor barrier should be installed prior to pouring the basement floor. Openings through the footings will allow any interior water to drain. A sump crock is installed within the building. This is where the drain tiles ties into. Any water around the footings will drain into the sump crock. A pump in the sump crock discharges the water outside and away from the building. For walkout basements, you might have your drain tile run out to daylight using gravity to discharge the water. Always check your local building codes. Sump pump and drain tile discharge can differ between municipalities.
A contractor may excavate around the house down to the footing and inspect the foundation wall and drain tile. If needed, they may repair the existing drain tile or install new tile. This may include a new sump crock as well. The foundation wall will be cleaned and a waterproofing system would be installed. Doing this is very labor intensive and expensive.
Another option is called an interior drainage system. A trench is cut in the concrete floor around the perimeter of the basement floor. This trench is lined with filter fabric and perforated drain tile is installed and covered with washed stone. A sump crock is installed where the perimeter tile ties into it. This design is to drain the water under the floor at the wall into the sump crock to be pumped out. This will also relieve the hydrostatic pressure at the foundation wall. A battery backup for the sump pump can add a layer of protection in the case of a power outage.