Why is my garage door gap uneven or the header sagging?
In short: A garage door that closes with a tapered gap at the bottom, or a header that dips over the opening, can mean one side of the garage foundation has dropped. It can also be a lintel or door-hardware issue, so the floor level, the opening and the brick above are checked together.
What does an uneven garage door look like?
- The closed door touches the floor on one side and leaves a wedge-shaped gap on the other.
- The weather seal is crushed at one end and open at the other.
- The header, the beam that spans over the door opening, dips in the middle or is visibly lower at one end.
- Brick above the opening has cracked, often at the corners of the opening.
This applies mostly to attached garages on slab-on-grade and post-tensioned houses.
Why does it happen?
Foundation settlement at one side
Expansive soils are common across most of Oklahoma, and seasonal moisture loss lets the clay shrink and the foundation edge move downward 4. If one side of the garage door opening drops more than the other, the opening tilts and the door no longer closes evenly. This is covered in perimeter drying settlement.
Engineering guidance lists racking of door and window frames among visible indications of foundation movement, and also uses poor door alignment and brick coursing that is not level as clues to movement 1. Inspector training material lists warped openings and sticking doors and windows among signs of settlement 5. Building officials note that foundation movement often cracks walls near window and door corners and can crack garage slabs, walkways and driveways 3.
Lintel and header deflection
A wide garage opening in brick veneer is spanned by a steel angle called a lintel. Brick industry guidance describes the crack pattern when a lintel is undersized: the crack is widest at the steel angle and tapers to nothing 2. That pattern differs from foundation settlement, which tends to produce diagonal or stepped cracks in the brick directly above the foundation 2.
Door hardware
Garage doors run on adjustable tracks and springs, and an uneven gap can come from the door itself rather than the structure. Measuring the floor and the opening separates the two.
How is it documented?
| Measurement | What it shows |
|---|---|
| Gap under the closed door at each end | Size of the tilt across the opening |
| Floor elevation at each side of the door | Whether the slab itself has dropped |
| Header level across the span | Whether the header dips (deflection) or tilts (settlement) |
| Crack shape in brick above | Lintel taper vs stepped settlement crack 2 |
A relative floor elevation survey is the engineering step beyond a visual first impression 1. Readings at the two sides of the opening are compared with each other and with the house floor, since a garage floor is not always built level. See elevation surveys and visible slab cracks.
Related
- Perimeter Drying Settlement (Edge Drop)
- Brick Separating from Window or Door Frame
- Stair-Step Brick Crack Wider at Top
- Visible Slab Cracks
- Elevation Surveys
Common questions
Why is the gap under my garage door wider on one side?
Either the slab or the door opening is out of level. If one side of the garage foundation has dropped, the floor and the opening tilt together and the closed door no longer meets the floor evenly. Door hardware and track adjustment can also cause an uneven gap, so the floor is measured before drawing conclusions.
What makes the brick above a garage door crack?
Brick over a wide opening is carried by a steel angle called a lintel. If the lintel deflects, the brick cracks in a pattern that is widest at the steel angle and tapers to nothing. Foundation settlement at one side of the opening can also crack the brick.
Are garage slab cracks a sign of foundation problems?
They can be. Building officials in expansive-soil areas list cracks in garage slabs among the signs of foundation movement, but concrete also cracks for other reasons, so offset and pattern are evaluated.
Sources
- Guidelines for the Evaluation and Repair of Residential Foundations, Version 3 Texas Section, American Society of Civil Engineers
- Volume Changes – Analysis and Effects of Movement (Technical Note 18) Brick Industry Association
- County Expansive Soils Policy & Procedures Roanoke County Development Services
- The Mystery of Expansive Soils STRUCTURE magazine
- Inspecting Foundation Walls and Piers International Association of Certified Home Inspectors (InterNACHI)
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