It might begin as a musty odor that can be bothersome, but is hardly cause for loss of sleep. However, when the dampness and water spots begin to appear, you could be about to experience every homeowner's nightmare: a foundation water leak. They're bad enough in unfinished spaces, but a leak in a living area can cause the room to become unusable and could lead to the growth of mold and mildew.
If a foundation leak appears in your basement, prepare for some detective work and repairs that can be costly. However, if you're planning a home addition that has a basement, as the old adage goes: "an ounce of prevention can be worth a pound of cure."
While you may be using a concrete contractor to pour your foundation, it never hurts to ensure the job is being done correctly. After all, if a leak occurs in the future, it will more than likely be you who has to deal with the problem. Here are a few items to watch for:
At the very least, all parts of the foundation wall that are below grade should be sprayed with an asphalt based waterproofing compound. Keyways are the metal strips that hold the forms together when pouring concrete walls. When the forms are removed, the ends of the keyways are visible in the concrete and can provide an avenue for water intrusion. All keyway ends below grade should be covered with tar for added protection when using a basic spray waterproofing.
If site drainage away from your addition might be an issue, applying a waterproofing membrane system such as CertainTeed's Platon can help keep the inside of your basement dry.
Very few foundation walls can be poured with a single truckload of concrete. When a significant amount of time passes between when a truck drops its load and the next truck shows up, a cold joint can be created between the two pours. A cold joint may affect the exterior cosmetics of your wall and can be a prime location for foundation leaks. Tell your concrete contractor that you don't want any cold joints in your addition's foundation walls.
Your foundation walls sit on a concrete footing and while waterproofing can help prevent moisture from entering at this seam, it's sometimes not enough. The concrete contractor should install drain tile around the exterior of the foundation wall where it meets the footing.
The tile needs to be surrounded with gravel to assist drainage and should be protected with filter fabric to keep soil from clogging the pipe's perforations. If you have a walk-out foundation, the drain tile should be daylighted in an area where it's free from obstructions.
While these tips can't guarantee that your addition foundation will be leak-free, a little bit of prevention can go a long way toward avoiding the expense of future cures.