Wednesday, October 3, 2012

Home Basement Contruction - Foundations

Home basement foundations require extra care and thought beyond what is typically used for an on grade slab. 

Many custom homes, especially in Del Mar and La Jolla California have basements. 

Home basements are a very usable design element in a home, especially where FAR’s (Floor Area Ratios) and land lot sizes preclude additional above ground building footage. Think of the benefit home basement construction ideas could offer the homeowner…perhaps a car lift which provides extra garage parking or a quiet space for a media room.

Typical home slab thickness for foundations are a thin (5” to 6”) layer of reinforced concrete with a supporting perimeter footing of thickened reinforced concrete (18” to 24” deep and wide) and thickened concrete at structural point loads within the homes footprint.  This works well both structurally and economically. 

Moisture control is ensured with a gravel layer topped with a heavy plastic layer directly below the concrete slab. This prevents water migration up to the concrete and stops water vapor penetration as well.  This moisture control is just not enough for most home basements.

Home basements by nature create a well for site and neighborhood water. They must endure higher water and water vapor pressure values. A daylight basement (or walk out basement) is able to use gravity to alleviate much of this pressure, but a typical home basement does not have that luxury. 

The first step in controlling water and allowing for structural needs is switching from a slab/perimeter footing model to a mat foundation model. In a mat foundation the bottom of the concrete is flat and level, this precludes trapping water under the slab between the footings. A continuous water barrier can be installed below the mat tying up into the basement walls. 

Drainage can be provided below and along side the waterproofing membrane. The key to a successful basement is relieving water pressure against the structure. A mat foundation with a properly installed below grade drainage system will alleviate that pressure and allow the waterproofing system to work.

A nice additional benefit for our custom home clients: it is typically less expensive to form a mat foundation than a standard detail once you are down in the basement hole. A bit more concrete, a bit less labor and a much better system!

Daylight basement ideas | Home basement Construction

Wardell Builders | info@wardellbuilders.com  | 858-793-4190 | Solana Beach, CA 92075
 
 

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