How to Build a Fence Gate That Won't Sag

Sagging gates are a geometry problem, not a hardware problem. The right diagonal brace makes the difference between a 10-year gate and a 1-year one.

A gate frame is essentially a rectangle, and rectangles are unstable — they rack into parallelograms under load. The fix is a diagonal brace running from the bottom hinge corner UP to the top latch corner. This brace works in compression, transferring the gate's weight back to the hinge post.

If you brace the other direction (top hinge corner down to bottom latch corner), the brace works in tension, which requires perfect joinery to stay tight. Wood compression joints stay tight for decades; tension joints loosen.

Use 2x4 pressure-treated lumber for the frame, half-lap or pocket-screwed at corners. Set the diagonal in place, mark the angle, cut, and screw it tight at both ends with structural screws. Then attach the fence pickets to the frame from the front.

Hang with heavy-duty gate hinges (Stanley or National brand T-hinges, minimum) and through-bolt them into the post — not just wood screws. For gates over 4 ft wide, install an Adjust-A-Gate kit ($30) which adds a turnbuckle for periodic re-tensioning.