Household guide
Garage Door Bottom Seals and Weatherstripping
How to identify the seal on your door, find the gaps a mouse can use, replace a worn bottom seal safely and slow down summer sun damage.
The seals on a garage door
A closed garage door is sealed in three places: along the floor, up both sides and across the top. Each uses a different part, and each wears at a different rate.
| Seal | Where it goes | Notes |
|---|---|---|
| Retainer bottom seal (T-end, bead or bulb) | Slides into an aluminium channel on the bottom of most steel sectional doors | Most common on modern doors; match the channel profile, not just the width |
| Nail-on or screw-on bottom strip | Fastened directly to the bottom rail of older wood doors | Usually a simple J or flat profile; replace fasteners if they have rusted |
| Threshold seal | Glued to the slab where the door closes | Raises the landing point to close gaps over a dipped or uneven floor |
| Stop moulding (side and top weatherstrip) | Nailed or screwed to the door jambs and header | A vinyl flap that should lightly touch the face of the closed door |
| Brush seal | Bottom or sides, often on roll-up doors | Copes with uneven surfaces but leaves a less complete barrier than a solid bulb |
Finding the gaps that matter
The quickest check is the daylight test. On a sunny day, close the door, switch off the garage lights and look along the floor and up both sides from inside. Any line of light is a path for insects, dust and hot air, and possibly for rodents.
Size matters more than you might expect. UC IPM's house mouse note says mice can squeeze under gaps ¼ inch tall, and its rat note says young rats can get beneath a door with only a ½-inch gap. As a rough field test, if an ordinary pencil slides under the seal anywhere along the door, the gap is already big enough for a mouse.
- Corners. Seals shrink and pull back from the jambs, so the corners are usually the first place light shows.
- Low spots in the slab. Garage floors are rarely flat. A seal that touches in the middle can float above a dip at one side.
- Gnaw marks. Ragged, chewed edges on the seal or the bottom of the door mean something has been working at it. UC IPM notes that rubber and vinyl are gnawable, and that door edges sometimes need metal covering where gnawing is a problem.
- Flattened or split bulbs. A bulb that stays flat when the door is open no longer springs back to fill small dips.
A good seal closes one route. The rest comes down to sealed bins and storage habits that deny pests food and shelter, so there is less in the garage worth getting into.
Replacing a retainer bottom seal
On most sectional doors this is a short job with basic tools. Before buying, measure the door width and look at the retainer from the end: single or double channel, and the shape of the slot. Taking a short cut-off of the old seal to the store avoids most mismatches.
- Open the door to a comfortable working height. Unplug the opener so nobody can run it, and put a locking clamp on the track just below a roller so the door can't move.
- Pull the old seal out of the end of the retainer. If it is stuck, a little soapy water helps.
- Clean grit and debris out of the channel, and check that the retainer isn't bent or cracked.
- Feed the new seal in from one end, both edges at once. A helper feeding while you pull makes this easier. Leave a little extra at each end, then trim it to sit snugly against the jambs.
- Remove the clamp, lower the door and repeat the daylight test.
- Reconnect the opener and test the safety reversal before you use it normally.
Leave springs, lift cables and the bottom brackets alone. They are under high tension. If the retainer itself is damaged where it meets the bottom bracket, that is a job for a trained door technician rather than a weekend fix.
Side and top weatherstrip and threshold seals
Stop moulding along the jambs should touch the closed door lightly along its full height. If the flap has curled away or cracked, replace the length rather than patching it. Fit the new piece with the door closed, pressing the flap just enough to make contact. Pushing it hard against the door can make the door bind as it opens.
A threshold seal is worth considering where the slab has settled or slopes toward the door. Clean and dry the concrete, position the seal with the door closed so the bottom seal lands on it, and use the adhesive the maker specifies. Low-profile thresholds are easier to drive over, but every threshold takes some wear from tyres.
Central Valley heat and sun
Rubber and vinyl seals harden, crack and shrink with age, and long hours of sun and heat tend to speed that up. A door that faces the afternoon sun through a San Joaquin Valley summer usually needs a new bottom seal sooner than one in shade. Stiff seals also stop conforming to the floor, which is how gaps open at the corners even when the seal still looks whole.
- Spring: daylight test and a look for cracks before the summer heat.
- Autumn: repeat the check before cooler weather, when mice are more likely to move indoors.
- Any time: wipe grit off the seal and out of the retainer, and follow the seal maker's care advice. Some advise against petroleum-based products on rubber.
- After any seal or floor change: rerun the opener's reversal test.