Maintenance Guide
How to Fix Garage Door Gaps and Replace Worn Seals
Gaps on the sides and bottom of a garage door let in rain, wind, dust, and rodents — and in a wet Oregon winter they quietly rot out the bottom panel and the jambs. Here is how to tell whether you need a fifteen-dollar seal or a real repair.
What causes garage door gaps
Almost every gap traces back to one of four things: a bottom seal that has flattened with age, side weatherstripping that has pulled loose or gone brittle, a slab or driveway that has settled unevenly, or a door that is no longer hanging square in its opening. The first two are straightforward homeowner fixes. The last two need to be diagnosed before you spend anything on rubber.
The four seals on a garage door
- Bottom astragal (U-seal / T-seal)
- The rubber strip in the retainer on the bottom panel. It compresses against the slab and is the first seal to flatten out. Replace it when it no longer springs back or when daylight shows under a closed door.
- Side and top weatherstripping
- Nailed or screwed to the jambs and header. Vinyl-flanged stop molding is the standard fix in the Pacific Northwest because it survives constant wet-dry cycling better than foam tape.
- Threshold seal
- Bonded to the slab itself. Best answer for a sloped or worn driveway where the concrete — not the door — is creating the gap.
- Panel-to-panel joint seal
- Between horizontal sections. If you see light between panels, the hinge or section is bent and the seal alone will not solve it.
Step-by-step: assess and reseal
- 01
Close the door and look for daylight
Stand inside with the lights off during the day. Trace every line of light: bottom, both jambs, header, and each panel joint. Photograph what you see — it tells you which seal to buy.
- 02
Check the slab with a level
Lay a level along the opening. If the concrete dips more than about a quarter inch, no bottom seal will close the gap on its own; you want a threshold seal or a shaped astragal.
- 03
Test the door for square
Measure jamb-to-door-edge at the top and at the bottom on both sides. If the numbers differ, the door is out of square — usually a cable off a drum, a bent track, or a worn roller. Do not chase that with weatherstripping.
- 04
Inspect the seal itself
Pull the bottom rubber out of the retainer at one end. Cracked, flattened, or shrunken rubber gets replaced. Torn retainers get replaced too — a bent aluminum retainer will not hold new rubber tight.
- 05
Replace the bottom rubber
Open the door, spray a little silicone lube in the retainer channel, slide the new astragal in from one end, and trim it slightly long. Close the door and confirm even compression across the whole width.
- 06
Re-do the side stop molding
Pry off the old molding, clean the jamb, then fasten the new vinyl-flanged stop so the flap just kisses the door face — pressed hard against the door it will drag, bind, and tear within a season.
When to stop and call a technician
- —Gaps that change size as the door travels — that is a spring, cable, or track problem, not a seal problem.
- —A gap at one top corner only, which usually means the cable drum spacing has slipped.
- —Light between horizontal panels, which means a bent section or failed hinge.
- —Any repair that requires loosening the torsion spring, drums, or cables. Those store enough energy to cause serious injury.
- —Rodents or standing water already getting in — worth an on-site look before the framing gets damaged.
Seal replacement in Estacada, Sandy, Portland and beyond
Mt. Hood Garage Doors replaces bottom seals, stop molding, thresholds, and the parts behind a door that will not sit square — residential and commercial — across Estacada, Sandy, Portland, the Oregon Coast, and the Bend area. Quotes are always free, and we are open Monday through Friday, 9am to 5pm.