Most of the time that cause is ordinary seasonal movement or how the wall was built. Sometimes it's the framing or masonry over the opening. Here's how to tell which way to lean before you pay for another patch.
Why opening corners crack
USG's guide to how jobsite conditions affect drywall names three kinds of movement: thermal (materials expanding and shrinking with temperature), moisture (materials absorbing and releasing humidity), and structural (the building itself moving, including foundation settling). All three concentrate at the corners of openings.
The CGC/USG construction handbook chapter on drywall problems calls a diagonal crack that starts at a corner "field cracking" and says it can start from the corners of doors and other weak areas in the wall. It lists several build-related causes worth asking about:
A panel joint that ends right at the corner of the opening. For veneer plaster walls, the handbook says the joints should be centered above openings, not at the corners.
Board cut past the corner when the opening was cut out, which leaves a hidden score line that later cracks.
Drywall fastened straight to a wide wood header, the beam over the opening. As that wood shrinks, it can crack the board.
In plaster over brick or block, cracks at door openings can come from poor lintel or frame construction.
Only the last one points at the structure. The others are about how the wall was put together, which is why the same crack can come back for years without the house getting worse.
Clues you can check yourself
Start with the crack itself. A line that runs straight along a taped seam is a different problem from a diagonal split across the board. Our guide to nail pops and cracks at drywall seams covers seam cracks.
Then look around the opening and the rest of the house:
Timing. If the crack comes back every heating season and the door works fine, seasonal movement is the likely cause. A door that only sticks in muggy weather is covered in our guide to a door that rubs in humid weather.
Doors and windows. A door that newly binds, a latch that no longer lines up, or a window that suddenly won't open is a stronger sign than the crack alone.
Other openings. Matching cracks above several doors or windows, especially on the same wall, suggest something larger than one bad joint.
Moisture. The handbook lists stains, paper peeling from the board, a soft board core and mildew as signs of water damage. A damp or stained crack is a leak question first.
Keep a record before anyone patches it again. Take one photo of the whole opening and one close-up with a ruler beside the crack, then repeat both from the same spot every few weeks. Write down when it was last repaired. Don't pry off trim or open the wall to look.
Who to call, and what to ask
If the crack comes back but nothing else has changed, a drywall or plaster contractor is the right first call. Ask whether the crack follows a panel joint, whether the board was cut past the corner, and what their repair changes this time. The handbook calls a tape-and-compound fix over this kind of corner crack a cosmetic treatment with "no guarantee that cracks will not reopen," so ask whether the joint needs to be relocated or a control joint added, which USG recommends to absorb movement.
Bring in a structural engineer if the cracks are growing, show up at several openings, or come with doors or windows that have started binding. Ask whether the header, the jack studs that hold it up (described in this Building America framing guide), the masonry lintel or the foundation needs a closer look.
Heavy snow is a special case. The Building America guide to snow loads lists sticking doors, a bowing structure and creaking sounds as warning signs of too much snow on the roof, and says to leave the building if there's any concern it could collapse. Don't try to brace anything yourself.
Permits in Philadelphia
Cosmetic patching and painting are regular maintenance. If the fix turns into replacing a header or reworking the framing or masonry around an opening, ask your contractor whether it needs a permit. The City of Philadelphia says you need a building permit for projects that change the interior or exterior of an existing structure or include major repairs that aren't part of regular maintenance. In Bucks or Montgomery County, check with your township or borough.
Before hiring, our checklist for hiring a home repair contractor in Philadelphia and Bucks County lists what to confirm, and our drywall repair page covers common wall repairs.