A gap under the garage door usually comes from a worn bottom seal, an uneven floor, or a door that stops short of the floor. It lets in rain, dust and pests, since mice can use any opening a quarter inch or larger. Replace a cracked seal first, then check the floor and the opener's close setting.
Why you can see light under the door
Stand inside with the door closed and look at the bottom edge. How the gap looks tells you a lot. An even gap along the whole width points to a worn or cracked bottom seal. A gap that is wide on one side and narrow on the other points to a door that is out of level or a floor that slopes. A gap in the middle with the edges touching points to a slab that has lifted or a high spot.
Garaga lists three common causes of a gap at the bottom: worn or cracked weatherstripping, an uneven or cracked concrete floor and poor slope outside the door.
Why it matters: pests, water and drafts
A gap is an open invitation. The U.S. Forest Service advises closing every opening of a quarter inch or larger to keep mice out, and it says steel wool and hardware cloth work because mice will not chew through them. It warns that mice chew through foam, so foam alone is not a fix.
Garaga also lists water damage, damage to stored belongings, higher energy bills and easier access for burglars as risks of leaving the gap.
What to check first
- The seal. Look for a flat, cracked or torn bottom seal. Replacing it is the usual first fix. See bottom seal replacement.
- The sides and top. Pests and drafts also use worn side seals; see side and top weatherstripping.
- The floor. The floor where the door meets it should be flat and free of large cracks. A threshold seal glued to the floor, or filler for a low spot, can close a floor gap.
- The outside slope. The ground outside should slope away from the door so water drains away.
- The corners. Check the bottom corners, where the seal and the side strip meet.
Fixing an uneven floor
If the seal is fine and the gap is uneven, the floor is the likely cause. Garaga suggests seal strips, epoxy, paint, tiles or mats to even out the surface where the door meets the floor. A rubber threshold strip glued to the floor is a common repair for a low spot, and the door's bottom seal presses against it.
Normal settling and hairline cracks are usually not a concern, according to the same source. Watch for new or widening cracks. If you see a big step or heave, a contractor should assess the slab.
The opener's close setting
If the door stops short of the floor, the opener's down limit may be set too high. Adjust the travel limit only as the owner's manual shows, then test that the door reverses on a 1-1/2 inch object. Chamberlain warns never to increase the force beyond the minimum needed to close the door. If the door does not reverse, stop using the opener and call a technician.
If the door is crooked or stops short for no reason you can find, a broken cable or a bent track may be the cause. See cable repair before you adjust anything.
Call a technician when the gap is a symptom
A seal is a small, simple part, but a gap can also be a sign that the door is off level, a cable has slipped or a panel has bent. Do not adjust springs or cables yourself. Our 12-point safety inspection is $89 and covers the springs, cables, rollers, tracks, sensors and opener, and we confirm any repair price after we see the door.
Where we come in
Emil Garage Doors repairs garage doors and openers in Southern California, and our city pages include Berkeley, Hollister and Coalinga. Call (213) 340-4232 or use the estimate form with a photo of the gap and we will tell you what the fix involves.
Questions people ask
Why is there light under my garage door?
The most common cause is a worn or cracked bottom seal. An uneven floor or a door that stops short of the floor can also leave a gap.
Can mice get under a garage door?
Yes. The U.S. Forest Service says to close every opening of a quarter inch or larger, and a worn seal or an uneven floor can leave a gap that size.
How do I seal an uneven garage floor under the door?
Garaga suggests seal strips, epoxy, paint, tiles or mats to even the surface. A glued rubber threshold strip is a common choice for a low spot.
Should I use foam to close a gap?
Not on its own. The U.S. Forest Service notes that mice chew through foam, while steel wool and hardware cloth hold up.
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