Foundations
The number one cause of foundation failures (80%) is uneven moisture around the foundation. The number one location for foundation problems is the southwest corner of the house (hottest and driest corner). Proper foundation maintenance includes adequate drainage away from the foundation (see Drainage section) and a consistent watering program.
Typical foundation watering programs for expansive clay soils in the DFW area
Indicators: Soil pulling away from the foundation or dry soil 3 inches deep next to the foundation are good indicators deep moisture restoration is in order.
Programs: Sprinkler systems are best as they run automatically, are easy to adjust for dry seasons and provide consistent moisture. Leaky hoses (hoses that sweat vs. spray) are also good. Place the hose 6" – 8” away from the foundation. if a hose that sprays is used, place the hose 24" - 36" away from the foundation.
Objectives: The intent is to slowly soak the soil, causing the soil to absorb the moisture like a sponge. When proper moisture has been restored the soil provides consistent and balanced support for the foundation. The objective has been attained when the soil stops pulling away from the foundation. If mature trees and scrubs are located near the foundation extra watering may be needed.
Concrete Slabs
Concrete Slab foundations also serve as floors within the structure. To protect the interior of the house from moisture rising into the building a “vapor retarder” is laid between the ground and slab.
Pier and Beam
Pier and beam foundations need adequate ventilation to eliminate / reduce any moisture build up. One (1) square foot of free vent area should be provided for every one hundred fifty (150) square feet of under floor area space and vent openings within three (3) feet of each corner.
All diagrams are from Code Check ® - Building, by Michael Casey, The Taunton Press, 2003. Code Check itself is based upon the International Residential Code (IRC) for 2003.