Garage door seals: the biggest hole in most houses

Do the arithmetic once and this hub stops feeling like an afterthought. A quarter-inch gap running the width of a sixteen-foot door is forty-eight square inches of permanently open hole — larger than most bathroom extractor vents, and open twenty-four hours a day. If the garage is attached to the house, that cold space shares a wall, a ceiling and usually a door with rooms you are paying to heat.

Garage sealing is also unusually satisfying because the parts are cheap, the gaps are visible, and the improvement is immediate. Most of a garage's leakage is at four places, and all four are reachable from a step ladder in an afternoon.

The four leaks, in order of size

1. 1The bottom of the door. The biggest one, and the one everybody knows about. Either the door's seal has perished — bottom seals — or the floor is uneven, which needs a threshold seal instead.
2. 2The jambs and header. A visible strip of daylight down at least one side on most garages. Cheap to fix and almost universally skipped: side and top seals.
3. 3The door into the house. Specified as an interior door, thermally an exterior one, and often the leakiest door you own: drafty door to the garage.
4. 4The person door to the yard, if you have one. An ordinary exterior door with an ordinary fix: door sweeps.

The decision that trips everyone up

Close the door on a bright day, stand inside with the lights off, and look along the bottom edge at floor level.

• An even line of light across the whole width — the seal on the door is worn. A bottom seal will fix it.
• Light in the middle only, or at one corner only — the slab dips or slopes. A bottom seal cannot fix this, because the door's bottom rail is straight steel and the floor is not. You need a threshold seal bonded to the concrete.
• No light, but water still comes in — the driveway or apron drains toward the garage. A threshold helps; drainage outside the door helps more.

This is the single most common wasted purchase in the category: two bottom seals bought in succession for a problem neither could solve. The full comparison is here, and the measurement method for a dipped slab is in garage door seal for an uneven floor.

Buy the length, not the nominal size

A nominal 16 ft door is usually a fraction over 16 ft, and a seal cut exactly to length leaves you short at the last corner. Buy the next size up. Trimming an inch off is trivial; being an inch short means another order and another weekend.

Material, briefly

Rubber and EPDM at the bottom, because that seal is compressed against cold concrete and has to spring back. Vinyl on the jambs and header, where it only has to bend, unless your winters are severe enough to make vinyl crack at the nail line. Brush belongs on a warped side jamb or a person door, not at the bottom of a garage door, because bristles pass water straight through. The longer version is in rubber vs vinyl vs brush.

Two safety notes

• Never work under an unsupported sectional door. Prop it or have someone hold it. If any job touches the springs, that is a professional's work — garage door springs are under enough tension to injure seriously.
• Do not seal the garage to the house for ventilation. A garage should be ventilated to outside, never into your hallway. Every seal on the house-to-garage door is on the side of safety, provided the door still closes and latches by itself.