How can I stop my slab leak?

Answered by Jeffrey Anderson ~ August 22, 2013 ~ No Comments

I need help! There is a leak between my slab foundation and sill plate. The area is above grade but the foundation does extend 4-5 inches beyond the house wall framing. I already removed the siding and checked that there is no moisture damage on exterior wall. Is there something I can do to seal the joint and make a permanent waterproof seal?


Jeffrey Anderson

Paula, the leak you describe is actually not all that unusual for homes built on concrete slabs. Gutters and proper grading usually eliminate much of the water that can find its way under the sill plate, but occasionally a driving rain may result in a leak. In your case, it sounds like the siting of the house or other issues could be causing it to happen more often. An uneven slab surface can also contribute to sill leaks as there can be gaps under the bottom framing plate.

There is a product called sill seal that framing contractors should install under the sill plate to prevent air and water intrusion in that area. However, over time it can lose its effectiveness, and if your home is older it may not even be installed.

There is a permanent fix for your water leak, but depending on your siding type it may require a little work. In my experience, the best method for eliminating the leak is to install metal flashing at the sill plate. The flashing can be purchased in rolls and is available in numerous colors so you should be able to find a close match to your siding.

Installing the flashing usually isn't too difficult but probably wouldn't be classified as being DIY-friendly as a siding break should be used to do the project properly. A siding break is a device that allows a sharp bend to be placed in metal along its length. There will have to be two 90 degree bends placed in your flashing.

The bottom piece of siding on your house will need to be removed. You may need to loosen several pieces above it to remove the siding without breakage. The flashing should be installed flush against the house where the siding was removed. It will extend down to the slab where it will have a 90 degree bend out and rest flush against the top of the concrete. The flashing should then extend out to the slab edge where it will have a 90 degree downward turn.

The flashing should extend up the side of the house about 6 inches and down the slab edge about 2-3 inches. The measurement of the flashing between the house and the slab edge will depend on how much of the slab surface is exposed.

If the two bends are tight, the flashing normally only needs to be secured to the house framing members with some large head nails. Once the flashing is in place, the siding can be reinstalled. This should take care of your sill leak once and for all.

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