Guide
Storm-proofing your garden: what lifts off, and when
Most of what gets damaged in an autumn storm is something the owner could have secured themselves in twenty minutes. Here's the order to do it in.
Wind pressure against a surface grows with the square of the speed. At 10 m/s the pressure is roughly 60 newtons per square metre, at 20 m/s just over 240, and at 30 m/s over 550 – close to 56 kilograms per square metre. That's why a seemingly heavy trampoline suddenly clears the fence: it has an enormous surface area relative to its weight, and the lift generated under the mat does the rest.
Roughly when things start to move
| Wind | Object | What happens |
|---|---|---|
| 5–7 m/s | Leaves, paper, empty cans | Roll and swirl away. |
| 8–10 m/s | Parasols, light cushions | Flap loose, parasols can buckle. |
| 11–14 m/s | Plastic chairs, empty bins | Wander across the garden, tip over. |
| 15–18 m/s | Trampoline, tarpaulin, building plastic | Lift off and fly. The most common source of damage. |
| 19–24 m/s | Garden tables, bicycles, scaffolding | Tip over or blow away, roof tiles come loose. |
| 25 m/s + | Trees, fences, shed roofs | Branches and whole trees fall, sheet metal tears off. |
Checklist before the blow
Bring in or tie down cushions, parasols, flagpole lines, toys and empty bins. Fold up and lay down garden furniture – furniture lying flat catches far less wind than furniture standing up. Anchor or dismantle the trampoline; simply turning it upside down is rarely enough. Tighten or remove tarpaulins, since a loose flap becomes a lever that tears apart whatever it's attached to.
Also check the roof of sheds and carports, clear gutters so water doesn't run into the wall, and shut hatches and windows on outbuildings. Park the car where no large branches can reach it. If you have a boat at a jetty: double the mooring lines, check the fenders, and expect high water with an onshore wind.
Common mistakes
The first is trusting the weight. A heavy object with a large surface area – like a sun lounger or a pallet of insulation – still moves. The second is securing things too late: once it's already blowing 20 m/s, it's dangerous to go out and wrestle with tarpaulins. The third is forgetting the neighbour's garden; whatever breaks your window often comes from there, so a chat in advance is cheap insurance.
After the storm
Don't go into a forest or under damaged trees until it has calmed down completely – hanging branches often fall hours later. Photograph any damage before clearing it up, which helps with insurance claims. Check the roof from the ground with binoculars rather than climbing onto a wet, possibly damaged roof.
Not sure how strong the forecast wind is? Enter the value in the visualiser and let a piece of garden furniture or plastic sheeting loose in the wind.
Visualise wind