How do I stop a fence blowing down in high wind?

Fences fail in storms in two places: the post snaps at ground level because the timber was already rotten, or the whole post levers out of the ground because the concrete collar was too small for the sail area above it. Everything else is detail.

Step by step

1. Find out which failure mode you have.Rock each post. A post that pivots in the ground is a foundation problem. A post that stays put while the panel flexes and pulls at its clips is a fixing problem. A post that snaps at the ground line was rotten.
2. Deal with the rotten posts first.No amount of extra bracing helps a post that has no sound timber at ground level. Replace it before doing anything else.
3. Increase the concrete collar where posts are moving.A 100mm post in a 300mm square collar 600mm deep resists far more than the same post in a narrow hole. Dig out, widen, re-concrete, and haunch the top above ground and sloping away.
4. Reduce the sail area at the top.Replacing the top 300mm of a 1.8m panel with trellis cuts the load noticeably and looks intentional. A hit-and-miss or slatted panel with gaps passes wind through the whole height.
5. Upgrade the panel-to-post fixings.Two clips per side is the usual minimum and often not enough on an exposed boundary. Add a third, use exterior screws rather than nails, and screw into the panel frame not the thin cladding.
6. Fit or repair the gravel board.A panel resting on soil rots at the bottom rail, and the bottom rail is what the clips hold. A sound gravel board keeps the fixing timber dry.
7. Brace the ends and any long unsupported run.A diagonal timber brace from post to gravel board at each end of a long run, on the sheltered side, adds real stiffness for very little money.
8. Check the whole run once a year in autumn.Push every post before the storm season. It takes five minutes and finds the post that would otherwise go down in the first gale.

Tips

• Wind loading rises steeply with height. Dropping a fence from 2.0m to 1.8m reduces the load on the posts more than most people expect.
• Storm damage to a fence is often excluded or subject to a high excess on home insurance — prevention is genuinely cheaper than a claim.
• If a whole run keeps failing, the site is funnelling wind. A permeable fence or a hedge behind it is a better answer than a stronger solid one.

Common mistakes

• Propping a leaning fence with a timber strut and leaving it — The prop transfers load to the ground and lasts one storm. The post itself has to be fixed or replaced.
• Filling gaps to make a fence more solid — It makes the wind loading worse, not better. A fence that leaks air survives storms that flatten a solid one.

If it doesn't work

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