The three causes
If you're in Fort Worth, Arlington, or anywhere in Tarrant County, chances are your drywall is cracking from one of three things: humidity-driven seasonal movement, slab foundation settling, or thermal cycling from your AC. Each one shows up at different spots on the wall, and each one calls for a different repair approach.
1. Humidity (the most common)
Texas summers run 70–90% humidity outside, and even with AC running indoors you'll see indoor humidity bounce between 30% (dry winter) and 60% (humid summer). Drywall absorbs and releases moisture with the air, expanding and contracting just slightly each time. Over years, this seasonal cycling shows up as hairline cracks, especially at inside corners (where two walls meet) and ceiling-to-wall seams (where the ceiling meets the wall).
How to spot it: hairline cracks following the corner or seam, often barely visible with overhead light but obvious with side-light from a window. Usually appears in multiple corners simultaneously, not just one. The crack opens and closes seasonally — wider in winter, narrower in summer.
The fix: tape and mud the corner, prime, paint. We coat with a flexible paintable caulk under the new tape if the corner has been moving for a while, which slows the recurrence. Typically $150–$300 per corner depending on length.
2. Slab foundation movement (the second most common)
Most North Texas homes are built on slab foundations. The Texas clay underneath those slabs swells when wet and shrinks when dry, which moves the slab — sometimes by 1–2 inches over a year. The slab moves, the framing moves, and the drywall has to move with it or crack. It usually cracks.
How to spot it: diagonal cracks running up from the corners of doors and windows are the signature. The crack starts at the upper corner of a door frame, runs diagonally up to the ceiling. You may also see cracks following the line of a structural beam in the ceiling. Foundation cracks tend to be wider than humidity cracks and grow over time rather than seasonally cycling.
The fix: patching the visible crack is straightforward — tape, mud, prime, paint. But the crack will return as the slab continues moving, often within 1–2 years. If the cracks are getting wider over time or you have multiple in the same room, get a foundation engineer's evaluation before you patch — patching a moving crack is whack-a-mole.
3. AC thermal cycling (the surprising one)
In summer your AC runs almost constantly, cooling the indoor air and the framing inside the walls. The temperature differential between the cool framing and the hot attic above creates expansion stress at the ceiling-to-wall transition. Over time, this shows up as cracks where the ceiling meets the wall, especially on exterior walls and especially in the rooms closest to the air handler.
How to spot it: cracks following the ceiling-wall corner on rooms with exterior walls, often worse in summer. Combined with stains if there's also AC condensate damage (a related but separate issue — see our drywall repair page for that).
The fix: same general approach as humidity cracks — tape, mud, prime, paint. AC-driven cracks tend to recur slower than slab-driven ones, so a good repair often holds for years.
When to call us vs. when to just paint
If your crack is hairline (you can barely see it), in just one or two spots, and not getting wider over time — caulking and painting is fine. Pick up some Sherwin-Williams MaxFlex (paintable elastomeric caulk) and have at it.
Call a handyman (or call us, at (817) 555-0142) if any of these apply:
- The crack is wider than a credit card.
- It's diagonal from a door or window corner.
- It's getting wider month over month, not just seasonally.
- There's a stain or bulge — that's water damage, different problem.
- You have multiple cracks in the same room.
If it's diagonal AND getting wider, get a foundation engineer first. We'll happily patch the crack after the foundation's been evaluated, but we don't want to patch something that's going to be pulled apart again in 6 months.