Seal the gap under a garage door

Fit a new rubber seal under your garage door to block draughts, water and leaves getting in.

SG-01Work out what type of door and seal you needCheck whether your garage door is up-and-over, roller or sectional, and see what the bottom rail is made of - metal or timber. Measure the width of the door and the size of the gap underneath when it's closed. This tells you whether you need a simple rubber bottom seal, a brush strip for an uneven concrete floor, or a floor-fixed threshold seal if the gap varies a lot along its length.

SG-02Buy the right sealFor a gap up to about 20mm, buy a rubber bottom seal cut to your door's width. For gaps that vary, or an uneven floor, buy a floor-fixed threshold seal instead. Take the door width measurement with you, or buy a roll slightly longer than you need and trim it later.

1 roll · Garage door rubber bottom seal (roll, cut to length)

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SG-03Clear the doorway and lay out your toolsOpen the door fully and sweep the floor underneath clean of grit and debris. Wipe the bottom rail of the door with a dry cloth so any adhesive or screws will grip properly. Lay your tools within reach so you're not stopping halfway through.

SG-04Remove the old seal, if there is oneUnscrew or pull out any old strip from the bottom rail. Scrape off old adhesive or perished rubber with a flat scraper. Clean out any track along the bottom of the door so the new seal will seat properly.

SG-05Measure and cut the new seal to lengthMeasure the full width of the door bottom rail and mark the seal to match. Cut rubber seals with a sharp craft knife, and aluminium threshold strips with a hacksaw. Cut it very slightly long rather than short, since a tight fit seals better.

SG-06Fit the seal to the bottom railIf the door has a factory-fitted track, push the seal in firmly along its length - no screws needed. If not, and the rail is aluminium or steel, drill a 3mm pilot hole every 150mm and fix with self-tapping screws. If the rail is timber, screw straight through with 25mm woodscrews without pre-drilling.

1 pack · Self-tapping screws (pack of 20)

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1 pack · Woodscrews 25mm (pack)

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SG-07Fit a floor-fixed threshold seal instead, if the gap is unevenIf you're fixing a threshold seal into the concrete floor rather than the door, use a 6mm masonry drill bit and check for pipes with a detector first - then still drill carefully and stop if you feel any resistance or see dust that isn't grey concrete dust. Push in plastic wall plugs and fix the strip down with 40mm screws every 200mm, then run a bead of exterior silicone along the leading edge to stop water creeping underneath.

1 each · Floor-fixed rubber threshold seal

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1 pack · Wall plugs and screws kit (masonry, 40mm)

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SG-08Seal the side edgesRun a thin bead of exterior silicone along the vertical edges where the seal meets the door frame or side rails. Smooth it with a wet finger for a neat finish. This stops water and draughts sneaking round the ends of the seal.

1 each · Exterior silicone sealant (tube)

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SG-09Test the door and tidy upOpen and close the door several times to check the new seal doesn't catch or drag on the floor. Wipe away any excess silicone before it cures. Dispose of the old seal and packaging, and sweep up any offcuts or dust.

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