Bottom Seals, Thresholds and Keeping Weather Out of the Garage

The rubber strip along the bottom of your garage door is the cheapest component on it and the one doing the most work against weather. In East Tennessee it takes cold, heat, water and UV, and it's usually the first thing to fail visibly.

What it does

The bottom seal — also called the astragal — compresses against the floor when the door closes, sealing the gap between the door's bottom edge and the concrete. It keeps out:

• Cold air in winter and hot air in summer
• Rain and runoff, which matters on a sloped driveway
• Leaves, dust and grit
• Mice, insects, snakes and everything else looking for shelter

On an attached garage, it also protects whatever's on the other side of the garage wall.

How to tell it's failed

• Visible cracking, splitting or tearing along the length
• The rubber has gone hard and no longer compresses
• Daylight visible under the closed door
• Water coming under the door after rain
• Leaves and debris in the garage after a windy day
• A section of the seal hanging loose

Squat down and look along the bottom of the closed door from inside with the light off. Any daylight is a gap.

Types

T-style (astragal) slides into a retainer track on the bottom of the door. The most common on modern steel doors, and easy to replace by sliding the old one out and the new one in.

Bead or U-shaped seals fit different retainer profiles.

Nail-on seals attach directly to the bottom edge, common on wood doors.

Getting the right profile matters — a seal that doesn't match the retainer won't stay in.

Replacing one

For a T-style on a steel door, this is genuinely a homeowner job:

1. Open the door partway to reach the bottom edge comfortably
2. Slide the old seal out of the retainer from one end
3. Clean the retainer track of grit and old debris
4. Lubricate the new seal with a bit of soapy water to help it slide
5. Feed the new seal in from one end, working it along
6. Trim to length

The main frustrations are a retainer packed with dirt and a stiff seal in cold weather. Warm the new seal before installing on a cold day and it goes in far easier.

If the retainer itself is damaged or rusted through, that's a bigger job.

When the floor is the problem

Plenty of older East Tennessee garage floors are not flat. Concrete settles, driveways slope toward the garage, and slabs crack and shift. If your floor has a low spot in the middle or a slope, a standard bottom seal will contact at the high points and leave a gap at the low ones.

Options:

• A taller bottom seal with more compression range covers a modest gap
• A threshold seal — a rubber strip bonded to the floor itself that the door closes against — handles a bigger gap and also stops water running in from a sloped driveway
• Both together for a significant gap

Threshold seals are genuinely effective for a garage that takes water off the driveway, which is common here.

Don't forget the perimeter

The bottom seal gets attention because it's visible. The stop molding along the sides and top of the opening has weatherstripping too, and on older doors it's usually hard, cracked and doing nothing.

Replacing perimeter weatherstripping is inexpensive and, on an attached garage, it makes as much difference as the bottom seal does.

The pest angle

A gap under a garage door is the main entry point for mice into a house. They need very little clearance. If you have a pest issue in the garage, the bottom seal is the first thing to check, followed by the corners where the seal meets the jambs — that's where gaps hide.

Do it with the annual check

Bottom seal, perimeter weatherstripping, lubrication, hardware tightening, balance test and safety reversal. That's an annual tune-up, and it's the difference between a door that lasts and one that doesn't.

We handle seals, thresholds and full tune-ups across Greeneville, Chuckey, Afton and Greene County. Call (423) 262-3147.