STRAND
FROM:
Strand Systems Engineering, Inc.
SUBJECT:
Foundation Maintenance and Care
Your home has been constructed using a concrete slab-on-grade foundation. This is the most commonly used type of foundation system in Texas. This type of foundation can be reinforced with conventional mild steel reinforcing, post-tensioned tendons, or a combination of the two. Most builders in the Texas use post-tensioning, along with some conventional reinforcing. All slab-on-grade foundations are designed to sit on top of the ground and float or flex with movement in the bearing soils. The foundations are built with a certain amount of rigidity, however, they are allowed by normal design parameters to deflect and bend a certain amount. Typically, foundation movements are caused by some change in the bearing soils beneath and directly surrounding the house. The most critical “changeable” factor in the sub-grade soils is the moisture content. This is important because most of the clay soils in the Dallas area are “active”, that is, they have an electromagnetic attraction for water and swell or heave upward when they can absorb water. On the other hand, these clays shrink and subside when they become dry. Thus it is said that in order to stabilize and control the movement of clay soils, it is necessary to control their access to water. If the moisture content under the foundation is maintained in a stable condition, the foundation itself will tend to be more stable, and deflection or cracking in the walls of the home should be minimized. When a home is constructed, the moisture content of the soil beneath the foundation is fairly uniform and evenly distributed. The slab foundation acts as a lid or covering, and protects and stabilizes it, except at the edges. Around the edges, swelling or subsidence can take place, depending upon environmental influences. If the soil outside the foundation along the perimeter is not well-drained, rainwater, sprinkler water or other irrigation water may puddle and slowly saturate the adjacent soil under the foundation. The saturated soil will swell and heave upward, causing “edge lift”. On the other hand, if watering is neglected, and the soil is exposed to summer sun and hot breezes, the soil will dry out, shrink, crack visibly, and subside, causi ng “edge drop” or “center lift”. Either of these conditions may progress to the point where the foundation of the home is deflected and the frame structure above is distorted and develops severe cracking. It is important that as a homeowner you realize that your foundation is more than just inert, passive concrete and steel. It is an element that will respond to changing conditions, and it needs understanding and maintenance if it is going to give satisfactory service.
The following are several recommended procedures, which will be helpful in this regard:
1. Be certain that the yard around the house slopes away from the foundation. Any standing or ponding water next to the foundation can cause undue unnecessary soil and foundation movement. Be sure the builder has sloped the yard for good drainage and that all drainage swales are working. A 5% slope is now recommended by the International Residential Code.
10003 TECHNOLOGY BLVD WEST | DALLAS TEXAS 75220 | 972 620 8204 | STRANDAE.COM
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