The foundation is the most important part of a house system, and once it's constructed, it's impossible to detect problems until the results show up in the house. The International Residential Code sets minimum standards and recommendations for residential construction. The template is followed by building authorities and modified to meet local conditions. Building regulations for foundations are especially significant for load-bearing characteristics and management of moisture for the foundation.
Foundation Structural Design
Soil is part of the structural design for foundations and it's load-bearing capacity determines the type of foundation that's suitable for the site. Slab-on-grade foundations are constructed on undisturbed or compacted ground. For footing and foundation walls, unless the soil is bedrock or the soils aren't susceptible to frost, the footings are buried below the frost line or else insulated from frost penetration. Seismic conditions or expansive -- clay -- soils require special foundation construction techniques.
Moisture needs to be channeled away from the bottom of the footings. In well-drained soils, a porous gravel channel at the base of the footings is sufficient, along with gravel backfill against the wall. Usually drainage tile -- perforated pipe -- is required and laid in a gravel channel at the bottom of the footings to capture water percolating from the surface, as well as groundwater. The drainage is channeled away from the house, or to a sump pit, where it's pumped away from the foundation.
As part of the strategy for keeping moisture from penetrating the walls, the regulations specify the height of the foundation wall above the street, or from the high point of the yard. The finish grade should be 4 to 8 inches below the top of the foundation wall, as regulations require. The grade should be sloped away from the house at a 5 percent slope -- or a 6-inch drop in 10 feet -- for a specified distance, usually 5 to 10 feet.
Dampproofing and Waterproofing Foundations
Any part of the wall that retains soil and encloses interior space has to be dampproofed to protect the foundation walls from water vapor migrating through the walls. The coating is usually asphalt-based, sprayed or applied to the walls from the top of the footing to the finish grade. Waterproofing is a more comprehensive treatment that keeps water from penetrating through cracks and defects in the walls. It's required in areas with a high water table or severe soil-water conditions.
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