Why a wooden gate starts to sag

A sagging gate is rarely a mystery. Wood moves, hinges loosen, and the post that carries the weight begins to soften at ground level. Most gates drop because the top hinge has pulled away from the post or the gate itself, or because the post has rotted below the surface. In some cases the gate was never braced properly in the first place. Before you start tightening anything, open and close the gate slowly and watch where the movement happens. If the hinge plates stay put whilst the gate drops, the problem is in the gate frame. If the whole hinge moves with the gate, the screws are loose or the timber behind them has failed. If the post itself shifts, you have a bigger job ahead.

Tightening and upgrading the hinges

Start with the simplest fix. A gate that has dropped by a few millimetres often just needs its hinge screws tightened. Use a screwdriver that fits the slot properly, and turn each screw firmly. If a screw spins without gripping, the hole has worn. Do not simply drive in a fatter screw, as this can split the stile. Instead, remove the screw, push a short length of wooden dowel or a few matchsticks coated in wood glue into the hole, let it set, then refit the original screw.

For a more permanent repair, replace the short screws supplied with hinges with longer ones. A 75mm or 100mm galvanised screw will reach through the hinge plate and deep into the gate stile or post. Drill a pilot hole first to prevent splitting. If the hinge itself is worn, replace both hinges as a pair. Stainless steel or galvanised hinges will outlast cheap mild steel in British weather. When refitting, pack the hinge away from the post slightly with a thin plastic or hardwood shim if the gate needs to sit further out. This can lift a drooping latch edge without moving the post.

Replacing a rotten gate post

If the gate post has rotted at the base, tightening hinges will not help for long. Probe the post with a screwdriver around ground level. If the blade sinks in easily, the timber is soft. You have two options. The first is to replace the whole post. Dig it out carefully, widen the hole, and set a new pressure-treated post in concrete with a gravel base for drainage. The second, less disruptive option is to cut the rotten section away and bolt a concrete repair spur to the sound timber above. Use M10 coach bolts through the post and spur, and fill any gaps with exterior-grade wood filler before painting.

Whichever route you take, keep the post clear of soil. A post that sits directly in wet earth will rot again within a few years. Set the concrete slightly above ground level and slope it away from the post so water runs off. A proprietary post-protection sleeve fitted below ground is a worthwhile extra. If the gate hangs between two posts, check both. A sound hinge post with a rotten latch post will still let the gate twist and drop.

Fitting a diagonal brace

A gate without a diagonal brace will always sag eventually, because the weight of the frame pulls the joints out of square. The brace is a simple triangle that transfers the load down to the hinge post. Fit it on the side of the gate that faces the garden, running from the bottom of the hinge stile up to the top of the latch stile. This orientation means the brace is in compression when the gate tries to drop.

• Cut a piece of 75mm x 50mm treated timber to length, angling the ends to fit neatly into the corners.
• Apply exterior wood glue to both ends and the face that meets the gate.
• Fix with two 100mm galvanised screws at each end, driven through the brace into the stiles.
• Check the gate is square by measuring the two diagonals. They should be equal.

If the gate already has a brace but it runs the wrong way, from the top hinge to the bottom latch, remove it and refit it correctly. A brace fitted the wrong way actually encourages the gate to drop.

Rehanging, aligning and protecting the gate

With the hinges tight, the post sound and the brace fitted, lift the gate back onto its hinges. Ask someone to support the latch edge whilst you check the gaps. The gate should sit evenly in its frame with a consistent 5mm to 10mm gap all round. If it binds at the top, adjust the top hinge by packing it out slightly. If it binds at the bottom, you may need to pack the bottom hinge. Small adjustments make a big difference.

Finally, treat every cut end and any bare timber with a good quality wood preserver. Pay particular attention to the bottom edge of the gate, the brace ends and the top of the post, as these are the places where water collects. A coat of exterior paint or stain will help, but the preserver is what protects the timber. Once the gate swings freely and latches with a satisfying click, you can step back and enjoy a job that should last for years.