Why water matters more than anything else
Expansive clay takes up water and swells, then dries and shrinks. A Texas licensing bulletin lists the controls that hold the swing down: drainage, plants, sprinkling, maintenance. The ASCE Geo-Institute calls keeping moisture even around a house the single best thing you can do, and says uniform moisture is less damaging than big swings.
San Antonio’s weather makes that hard. The area’s driest year recorded 10.11 inches of rain, and its wettest 52.28 inches. In one October 1998 storm the city saw 11.26 inches in a day.
The fixes, cheapest first
- Gutters and downspouts. Clean, sound, and discharging away from the slab. The ASCE Geo-Institute says at least at least 3 feet from the house, and ASCE Texas says to go well past the edge of the foundation and past any planting beds.
- Grading. Build soil up so water falls away from every side.
- Flower beds and flatwork. Keep planting beds from holding water against the wall; fix sunken walks that tilt toward the house.
- French drains or surface drains. For lots where water has nowhere else to go.
- Sump or yard drains. For worst-case lots, and typically a bigger job.
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Get the grading right
The ASCE Texas Section target is 5 percent (6 inches in 10 feet) for the first 10 feet. The Geo-Institute guide’s is 3 inches of fall in 5 feet. The ASCE Geo-Institute guide says to use clay, not sandy soil next to the house, and to keep the dirt line several inches below the top of the foundation.
Trees, beds and flatwork
Trees pull water out of clay. The ASCE Geo-Institute says to plant trees farther from the house than their mature height. On the other hand, ASCE’s Texas Section warns that removing a large tree near a house can cause upheaval as the soil rewets. Talk to someone who has measured your lot before taking one down.
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Pier and beam houses
The crawl space needs to stay dry too. The FPA says ponding water under a block-and-base house can let support blocks move, settle, or tilt. The pier and beam page covers vents, drainage and ground clearance.
Watering in dry spells
Watering soil next to the house can slow shrinkage, with limits. San Antonio’s SAWS rules decide which tools you may use: a hand-held hose is allowed any time on any day in Stage 3, while a soaker hose is allowed once a week. The ASCE Geo-Institute suggests soaker hoses 18 inches from the foundation, and also cautions that the goal is just enough to keep plantings alive and growing, not soaking. ASCE’s Texas Section issues a caution against excessive watering. The watering guide covers it in detail.
If a perimeter watering system is already part of a repaired foundation, the FPA warns that over-watering can cause adverse movement, and that dramatic foundation settlements could occur if it is turned off.
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Drainage and the repair plan
Drainage doesn’t replace piers when a foundation has already dropped, but it’s part of any good plan. The FPA says a repair leaves the foundation open to continued movement if drainage stays poor, and that should not be considered a repair. In other words, drainage and watering are maintenance. Ask any contractor what they’d change outside the house and who does it.