A front door that starts sticking in July. A new crack in the drywall above a bedroom doorway. A line across the garage floor that wasn't there last summer. Each of those can be a sign that the soil under your house is moving.
That isn't a reason to panic. It's a reason to pay attention through the dry months, and to do the simple thing Texas A&M AgriLife's guidance points to: keep the soil around your foundation evenly moist.
If your home sits on a concrete slab, as a lot of DFW homes do, the soil under it dries out and shrinks in a hot, dry stretch. What matters is how evenly it changes, and what you're doing about it.
This is the foundation check we'd like every DFW homeowner to run each summer. The good news is that keeping up with it costs little: a soaker hose, a timer and some attention.
What Is Actually Happening Under Your House
Much of DFW sits on expansive clay, the "black gumbo" that turns rock-hard in August and sticky in March. The Dallas County Master Gardeners, a Texas A&M AgriLife Extension program, describe it plainly: the clay swells when it's wet, and in summer and drought it dries out and shrinks. Build a slab on top of it and the slab rides along.
After a wet spring, the soil is full of moisture and your slab sits evenly on it. Then the rain stops, the heat settles in, and the clay under and around the house starts to dry. It shrinks and pulls away from the edge of the slab, and gaps open up.
If the soil dried out evenly across your whole lot, the house would settle a little and you might never notice. But it doesn't dry evenly. The shade under a big tree dries differently from the sunny side of the yard. The flowerbed by the front porch dries differently from the strip of grass next to the driveway. The corner where a downspout empties dries differently from the corner that gets no runoff at all.
That uneven drying is what does the damage. The slab doesn't just sink, it twists. One corner drops while another holds steady, and somewhere in the middle of the house a doorframe stops being a rectangle.
The Warning Signs to Walk Your House For
Take a slow walk around your house, inside and out. Here's the checklist.
Doors. Open and close every interior door. Does one stick, catch at the top, or refuse to latch where it latched in the spring? A door that no longer fits its frame is one of the common signs that a slab has moved.
Drywall corners around doors and windows. Look at the top corners of every doorway and window. Are there cracks angling up and out from the corner, or stair-step cracks along the seams? A hairline crack in the paint on its own isn't the one to flag. The ones to flag are getting wider, growing over a few weeks, or running through the trim and not just the paint.
The brick or stone outside. Look for stair-step cracks in the mortar, the diagonal zigzags that follow the brick joints. Look at the gap between the trim around your windows and doors and the masonry. A gap that wasn't there before is worth noting.
Floors. Take a level into a few rooms, or set a marble on the kitchen floor. If it rolls noticeably and consistently one way, that can be the slab moving, not just an old house.
Around the edge of the slab. Look at the dirt right against the foundation. Is there a gap between the soil and the concrete? That's the soil shrinking away. The soil should be touching the slab. When it isn't, the next rain can run straight down along the foundation.
If you see several of these together, especially if they're getting worse over a few weeks, that's the time for an independent assessment from a licensed structural engineer. A repair company's free inspection comes from someone who sells repairs. An engineer's report comes from someone who doesn't, and it's worth paying for.
How to Water Your Foundation
Through the hot, dry months, water the soil around your slab. On purpose, on a schedule, for as long as the dry weather lasts. The goal is what the Master Gardeners call "consistent, moderate watering": even moisture, not a flood.
The spacing and the depth come from Texas A&M AgriLife's Dallas center, in guidance published by the City of Richardson. Lay a soaker hose or drip line six to 18 inches out from the foundation, not against it. Run it until the soil is moist six to eight inches down. Cover the hose with mulch and run it early in the morning. How long that takes depends on your hose and your soil, so check rather than guess.
To check, push a long screwdriver into the soil near the slab. If it goes in six inches easily, the soil is watered. If you can't push it in, the soil needs more water. The gap check from the walk-around works too: if the soil is touching the slab all the way around, your moisture is good. And don't overdo it. The Master Gardeners warn that too much water under a house can make the clay heave and lift the foundation.
If you live in Fort Worth, the sprinkler schedule may not be the rule that applies to your soaker hose. The city's watering page says a hand-held hose is allowed at any time and that drip irrigation is there to protect structural foundations, trees and other high-value landscaping. The city's 2014 water conservation ordinance goes further: it lets a handheld hose, a soaker hose or drip irrigation run on any day, at any time, for that same reason. The twice-a-week schedule and the ban on watering between 10 a.m. and 6 p.m. are for sprinklers and irrigation systems. Drought stages tighten the rules, and other DFW cities write their own, so check your city's current rules before you set the timer.
