Why wooden gates sag
A gate frame is a rectangle, and a rectangle with joints that can flex wants to turn into a parallelogram. The gate is held at one side by its hinges, so the free end, the latch side, drops under its own weight. Over time the corner joints loosen, the wood can shrink, swell and warp, and the drop gets worse. The gate starts to drag on the ground or fails to line up with its latch.
A triangle does not change shape without bending or breaking its sides, so a diagonal member makes the frame stiff. That is the whole idea behind bracing.
The direction matters
Where a brace runs makes a big difference, and getting it backward wastes the effort.
- A solid wooden brace works in compression. It pushes. It should run from the bottom corner on the hinge side up to the top corner on the latch side. Weight on the latch end pushes down on the lower end of the brace, which pushes against the frame near the hinge.
- A cable, rod or wire works in tension. It pulls and cannot push. It runs the other way, from the top corner on the hinge side down to the bottom corner on the latch side. As the latch end tries to drop, the cable is stretched tight and resists.
If you install a cable in the compression direction, it will just go slack. If you install a wood brace in the tension direction, it will not hold the latch end up. When in doubt, picture which way the free corner wants to fall and which way the brace would be pulled or pushed.
Wooden braces
A diagonal board is the traditional choice and is common on farm gates and board-style yard gates. It is usually cut at the right angle for the frame and fastened to each horizontal rail it crosses. Plenty of well-made gates have one built in from the start. Key points:
- The ends must sit tight against the corner of the frame so that the brace takes load as soon as the gate shifts.
- Fasten it at each crossing with exterior-rated screws or bolts that suit the wood.
- Use the same kind of weather-resistant lumber as the frame, since a brace that rots does no good.
A built-in diagonal brace adds some weight, but it is a simple and visible solution that needs no adjustment.
Anti-sag cable kits
An anti-sag kit usually consists of a steel cable or rod, corner brackets or eyebolts, and a turnbuckle or tensioner. The brackets attach to two opposite corners of the frame and the cable runs between them. Turning the turnbuckle shortens the cable and lifts the free end of the gate.
The advantages are obvious. These kits can be added to an existing gate, are adjustable, and are less visible than a big board. They are also quite handy as a repair for a gate that has already started to droop.
There are limits:
- A kit corrects the frame. It does not fix a leaning or loose post, a worn hinge or a cracked rail.
- Tighten it too much and you can pull the frame out of shape or crack a joint. Many makers advise snugging the cable gradually.
- Cables and brackets in wet climates need the same corrosion protection as other hardware, which is covered in the article on corrosion-resistant hardware.
Adding a kit to a sagging gate
The exact steps depend on the kit, so follow the manufacturer’s instructions. In general:
- Check the posts. If the hinge post leans or moves, fix that first, since otherwise you are chasing the problem. The article on straightening a leaning fence post covers it.
- Check the hinges and their screws. Replace any that are loose or bent.
- Support the free end of the gate on a block or jack so that the frame sits square, with an even gap along the top and sides.
- Mount the brackets at the correct corners, so the cable runs from the top hinge corner to the bottom latch corner.
- Pull the cable snug and adjust the turnbuckle a little at a time, checking the gap with a level or tape measure.
- Remove the support and test the swing and the latch. Fine-tune and check again.
Wear gloves, since cable ends can fray and have sharp strands. A gate can be heavy, so have a helper support it.
Other ways to keep a gate square
Bracing is not the only approach. Heavy gates sometimes use metal corner plates, bolted Z or K frames, or steel inside the wood. A wheel or support roller at the free end carries some of the load, which is discussed in the article on gate wheels. Using adjustable hinges can also help to re-level a gate that has shifted, and the article on hinge types covers them.
It is also worth thinking about weight and size. A gate that is very wide may be better as two narrower leaves than as one wide leaf, which is where a drop rod becomes useful for the leaf that stays fixed.
Prevention
Most of the usual gate sag causes can be reduced at the planning stage. Use sturdy posts set deep enough for local conditions, size the hinges generously, make the frame with strong, tight joints, and add a diagonal brace when the gate is built. Check the posts each season, particularly after storms and freeze-thaw cycles, since frost heave can change post position. Local building codes and neighborhood rules may affect gate size and construction, so check them if you are building or rebuilding.