How do I stop a wooden gate warping?

Two different problems get called warping. A gate that drops at the latch corner has racked — the rectangle has become a parallelogram. A gate whose surface no longer sits flat has twisted, which is the timber moving because one face is losing and gaining moisture faster than the other.

Step by step

1. Work out which problem you have.Hold a straightedge diagonally across the gate. If the frame is out of square but flat, it has racked. If the corners do not sit in one plane, it has twisted. The fixes are different.
2. Get the brace direction right.A compression brace must run from the bottom of the hinge stile up to the top of the latch stile. Fitted the other way it does nothing at all, and this is the single most common gate mistake.
3. Fit an anti-sag wire if a brace will not fit.A tensioned wire with a turnbuckle runs the opposite way to a compression brace — from the top hinge corner down to the bottom latch corner. Tighten just enough to bring the gate square.
4. Pull a racked gate square before fixing anything.Take the gate off, lay it flat, and clamp or lever it back to square, checking the diagonals are equal. Then fit the brace to hold it there.
5. Seal all six faces to stop twist.Twist happens when one face dries faster than another. Preservative or stain on the front, back, both edges and both ends — the top end grain is the one everyone misses and the one that drinks water.
6. Cap or bevel the top edge.A weathered or capped top sheds water off the end grain rather than letting it soak in. This alone prevents most gate twist.
7. Check the hinge post is not the real problem.A post leaning out of plumb makes a perfectly square gate look sagged. Level the post before blaming the gate.
8. Store or dry a replacement flat.A new gate left leaning against a wall for a fortnight in the sun will twist before it is hung. Store flat and supported, out of direct sun.

Tips

• Equal diagonals mean a square gate. Measure both corner to corner — it is faster and more reliable than a square on a large frame.
• Retighten an anti-sag wire once a season rather than heaving it tight in one go. Over-tensioning pulls the gate past square the other way.
• Hardwood or a well-braced ledged and braced softwood gate resists both problems better than a light framed gate.

Common mistakes

• Fitting the diagonal brace the wrong way round — A timber brace only works in compression, so it must rise from the hinge side. Running it from the top hinge corner down puts it in tension, where timber and its fixings do nothing useful.
• Treating only the visible faces — The untreated back and top take up moisture faster than the sealed front, and the gate bows towards the drier face. Seal everything.

If it doesn't work

Questions people ask