STRUCTURAL DESIGN

The major structural components of a crawl space are the wall and the footing (see Figure 3-2). Crawl space walls are typically constructed of cast-in-place concrete, concrete masonry units, or alternative systems like insulated concrete forms (ICFs). Crawl space walls must resist any lateral loads from the soil and vertical loads from the structure above. The lateral loads on the wall depend on the height of the fill, the soil type and moisture content, and whether the building is located in an area of low or high seismic activity. Because of the large number of variables involved in foundation structural design, final determination of wall thickness, concrete strength, footing dimensions, and reinforcing should be made after consultation of locally-enforced building codes or design by a licensed structural engineer.

In place of a structural foundation wall and continuous spread footing, the structure can be supported on piers or piles with beams in between. These beams between piers support the structure above and transfer the load back to the piers.

Concrete spread footings provide support beneath concrete and masonry crawl space walls and/or columns. Footings must be designed with adequate size to distribute the load to the soil.  Freezing water beneath footings can heave, causing cracking and other structural problems.  For this reason, footings must be placed beneath the maximum frost penetration depth unless founded on bedrock or proven non-frost­ susceptible soil or insulated to prevent frost penetration. Since the interior temperature of a vented crawl space may be below freezing in cold climates, footings must be below the frost depth with respect to both interior and exterior grade unless otherwise protected.

Where expansive soils are present or in areas of high seismic activity, special foundation construction techniques may be necessary. In these cases, consultation with local building officials and a structural engineer is recommended.