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Re: Underground garage

From: info@builderswebsource.com
Category: Foundations and Basements
Remote Name: 63.198.181.43
Date: 15 Jan 2002
Time: 08:37 AM

Comments

The maximum driveway slope for residential construction varies from city to city. For example, where we live, a maximum 18% slope is allowed (which is very steep). Other cities allow only an 8-10% slope, and 6% for commercial buildings. You must check with your local building department to determine what the maximum allowable slope is for your area.

Keep in mind that if the drive slopes towards the garage (as opposed to away from the garage), you will need a comprehensive drainage plan, otherwise you'll end up with a real problem during rainy months. Typically a 2% slope AWAY from the garage is desired for drainage. Sometimes a swale is specified near the opening of the garage with a suitably sized drainage ditch/grate at the bottom of the swale. Perimeter French drains are also recommended, along with a way to evacuate the water (such as a redundant pump).

As to using the existing basement wall, this will depend entirely on structural considerations. Since basement walls have to retain tremendous pressure from soil and water, we strongly urge that you consult a licensed structural engineer who can evaluate your existing conditions first hand and make recommendations about any load-bearing walls that will be required to support your underground garage.

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