Garage door weather seal: find the gap before you buy the rubber

A garage door seals in four places. The bottom edge against the slab, the two sides against the jambs, the top against the header, and the joints between the sections. Each is a different part, installed differently, and the hardware store sells all of them under the same words. Grabbing the first roll is the usual outcome of searching “garage door weather seal”.

So skip the roll for now. Close the door on a bright day, stand inside with the lights off, and look at the floor before you look at the door.

Where is the draft coming from?

What has collected on the concrete tells you which seal failed.

• A fan of dust and dry leaves at one bottom corner, and nowhere else. The slab has settled or the bottom seal has gone flat at that end, and the rest of the seal is fine.
• A thin line of grit along the whole bottom edge. The bottom seal is done. Around DeKalb the line is easiest to see in October, when the combines are running west of town and the harvest dust drifts under every door with a tired seal and shows up as a brown stripe inside.
• Daylight down one side of the door, or a draft you can feel on your hand a foot off the floor. That is the side seal on the jamb, which is a different part entirely.
• A water line across the floor after a rain, wider in the middle than at the corners. The slab pitches into the garage, or the apron outside has settled toward the door, and no seal fixes a floor that drains the wrong way.
• Light in horizontal lines between the panels with the door closed. The section joints, which usually means the door is out of square, and rubber is not the answer.

Mice use the corner gap. If you have had them, that corner is the first thing to fix.

Note which pattern is yours before you buy anything or call anyone. It is the difference between a strip of rubber and slab work, and on our end it decides what goes on the truck.

How do I know the bottom seal needs replacing?

Press the seal with a thumb. A bottom seal that is doing its job dents and springs back. One that has gone hard, cracked along the fold, or taken a permanent flat set at the corners is finished. The seal on an older DeKalb door has usually spent a dozen winters being compressed against a frozen slab, and rubber only takes that for so long.

Then look at how it is held on. That decides which replacement to buy.

Most steel doors carry the seal in an aluminum retainer along the bottom edge. The rubber has T-shaped ends that slide into channels in the retainer, and the size of that T is what you match. A quarter-inch T and a five-sixteenths T look alike on the shelf and do not interchange. Some retainers take a round bead instead. Older wood doors have no retainer, and the seal is a strip nailed to the bottom edge. Cut a two-inch piece off the old seal and take it with you, or send us a photo, and the guessing stops.

On a steel door with a clean retainer, the swap is a homeowner job. Slide the old rubber out one end, slide the new one in with a little soapy water, cut it long, tuck the ends. One thing at the bottom of the door is not a homeowner job. The brackets at each corner hold the lift cables, and the cables are under spring tension with the door closed. The seal slides past them. Leave the brackets bolted.

We do not carry a separate line for the seal on our price table. It is a small part that goes on during a tune-up visit, and the tune-up itself runs $89 to $129.

Bottom seal or threshold seal: which one do I need?

The bottom seal is on the door and moves with it. The threshold seal is a raised rubber strip glued to the slab where the door lands, and the door’s own seal compresses against it. A threshold exists to make up for a floor that is not flat.

If the corner-fan pattern from the floor check is yours, and the bottom seal itself is still soft, the slab is low at that corner. A taller bottom seal in the same retainer closes a gap up to about half an inch. Beyond that, a threshold strip fills what the rubber cannot. That is common in the detached alley garages in the old blocks between downtown and the university, where the slab has had ninety years to settle toward the alley.

A threshold has one drawback that nobody prints on the package. It is a dam. It keeps water out, and it keeps water in. Snow melting off two cars has to go somewhere, and if the floor drains toward the door, the threshold holds that water inside as a puddle and then an ice sheet. On a garage with a floor drain, fine. On one that drains out the big door, it trades a draft for a skating rink.

Do the side and top seals matter?

More than people think, because they are the seals nobody replaces. The jamb seals run up both sides and across the top, usually a vinyl strip with a flexible flap that presses against the face of the closed door. They shrink back from the corners over the years, or get painted stiff along with the trim.

Two ways they go wrong. Too loose, and there is daylight down the side. Too tight, and the flap drags on the door every cycle, which makes the door louder and puts a scuff line down the panels. The fix is the same strip, nailed on with the flap barely touching the door. In the wood-framed openings of DeKalb’s prewar garages the jamb itself is often out of plumb, and the strip gets set to follow the door, not the wood.

With the door closed, run a hand up each side from the inside on a windy day. Where the draft is strongest, the flap has pulled away.

When a new seal will not fix the gap

Some gaps are not seal gaps, and new rubber on one of those is money spent twice.

A bottom seal cannot hold on a rusted retainer. Steel doors rust from the bottom edge upward, and once the retainer is pulling away from a rotted lower edge, the seal droops between the screws no matter how new it is. That is a bottom section, and a single section runs $250 to $800 installed. If the rust has climbed into the second panel too, the honest number is the whole door, and the installation page sets a new single-car door at $1,200 to $2,600 and a two-car at $1,800 to $4,500, and that price includes a new seal in a new retainer.

A door that closes crooked leaves a wedge of daylight at one bottom corner that no seal can fill. A wedge means a cable has stretched or a roller has left the track. If the door is visibly crooked or a cable hangs loose, stop cycling it and treat it the way our emergency page describes an off-track door. Every extra cycle on a racked door costs more than the seal did.

A stiff seal can also make the opener refuse to close. The door presses into the hardened rubber at the last inch, reads it as an obstruction, and goes back up. The won’t-close guide walks through the close-limit setting, and a fresh seal often solves that one before any adjustment is needed.

And the ice bond. When meltwater freezes along the bottom seal overnight and the opener rips the door free in the morning, the seal is what tears. Free the ice first, the way the won’t-open guide says. A seal rated to stay soft below zero survives that morning better than a hardware-store roll does, and it is the one we put on.