During the Bay Area's rainy season, torrential storms can present a drainage challenge to your roof, yard and basement.  What can you do to prevent dampness and flooding?

One of the easiest steps you can take is to make sure that the downspout from the gutter on your roof significantly redirects rainwater away from the foundation of your house. Most downspouts, particularly ones on older houses, simply empty onto a splash-block. While a splash-block absorbs some of the energy of a pounding stream, rainwater can still pool near the foundation of your house. In a heavy storm, this is bad news — especially if the soil around your house is mostly clay because it drains poorly. Gallons of water could gush from the roof and eventually seep into your basement through the foundation. Instead of using the standard downspout that empties onto a splash-block, you should extend your drainpipe out and underground, so that roof water empties away from your foundation. If you have a basement sump pump, make sure to connect it to this drainage system, so that it does not simply discharge water next to the foundation.

Another do-it-yourself preventative measure is to make sure the ground immediately surrounding your foundation slopes away from your house. This gradation should direct water to the lowest point of your yard. Never landscape so that the ground slopes down towards your foundation or you will likely find water in your basement after the next storm. 

However, if your house sits on a hill –– and San Francisco is extremely hilly –– and you cannot prevent water from flowing down into your yard from a higher point, you could install a linear French drain. This is a relatively inexpensive and easily constructed drainage system that controls the flow of water through the soil. For instructions on how to install one, as well as details on other drainage solutions, see AsktheBuilder.com.   

Finally, remember that severe storms can also cause flooding from sewage back-ups. Be sure to check the position of all drains in your home relative to the sewer vent on the sidewalk outside. If any drains or fixtures sit lower than the sewer vent, you should install a back-flow mechanism to prevent sewage contamination. Call the San Francisco Plumbing Inspector at (415) 558-6054 to discuss the best location for this kind of apparatus.