How do I anchor a shed down so it does not blow away?

Fixing a shed to its base, the anchor types that suit slab, timber and gravel bases, and the roof detail that lifts first.

Difficulty: beginner
Time: 2 hr
Read: 3 min
Safety: caution

Short answer

Bolt the shed floor bearers down to the base — expanding anchors into concrete, ground anchors or screw-in earth anchors on a gravel or timber base. Then check the roof: it is the roof that lifts first, and the fix is more fixings at the eaves and gable edges.

A shed is a light box with a large roof. In a gale the wind gets under the eaves, lifts the roof, and the walls follow. Anchoring the floor stops the whole shed moving; fixing the roof properly stops the failure that usually happens first.

Safety

Do not anchor into a base you have not checked. Drilling into a concrete slab over a buried service, or into a wall that turns out to be a boundary wall you do not own, causes problems that outlast the storm. Have a second person hold panels when working on a shed in windy conditions.

Step by step

Check what the shed is standing on.A concrete slab takes expanding anchors. A timber-framed base takes coach screws through the bearers. Paving slabs on sand take ground anchors driven into the soil beside the shed. Gravel alone needs earth anchors.
Fix the floor bearers to the base.Two anchors per bearer minimum, near the ends, through the bearer into the slab. Use a washer under each head to spread the load into the timber.
Use screw-in earth anchors on soft bases.Auger-style earth anchors wind into firm soil and take a strap or a wire over the shed or fixed to the frame. Two on each long side, tensioned evenly.
Check the roof fixings before anything else.Most shed roofs are pinned with a handful of nails. Add screws through the roof deck into every rafter and into the wall top plate, at 200-300mm centres round the perimeter.
Close the eaves overhang if it is exposed.Wind getting under an open eaves overhang is what generates the lift. A soffit or a fascia closing the gap reduces it substantially, provided you keep the ventilation path.
Fix the wall panels to each other and to the floor.Flat-pack sheds are usually held together with a few screws at the corners. Add screws down each corner joint and along the bottom rail into the floor.
Fit storm straps if the shed is very exposed.Galvanised straps over the roof to ground anchors on either side. Ugly, and effective in a genuinely exposed position.
Re-check the fixings each autumn.Timber shrinks and screws loosen. A five-minute check with a screwdriver before the storm season is the whole maintenance requirement.

Tips

Do the roof before the floor. The roof is what fails first and it is the cheaper fix.
Stainless or galvanised fixings only — anchors that rust away have anchored nothing.
A shed sheltered on three sides can still be in a wind funnel. Watch which way leaves and litter collect around it.

Common mistakes

Weighting the shed down inside instead of anchoring it — The load is on the floor, and the roof and walls lift off the floor. Weight inside does nothing for the failure that actually occurs.
Anchoring only at the corners — The long walls flex between the fixings and the bottom rail pulls off. Fix at intervals along each bearer, not just at the ends.

If it doesn't work

Roof lifted at one corner in a gale

Cause: Too few fixings at the eaves, wind getting under the overhang — Fix: Screw the roof deck into every rafter and into the top plate at close centres, and close the exposed eaves.

Whole shed shifted on a slab

Cause: Not fixed down at all — Fix: Expanding anchors through the bearers into the slab, two per bearer minimum.

Anchors pulling out of a gravel base

Cause: No purchase in loose material — Fix: Use screw-in earth anchors driven into the firm ground below, or lay concrete pads at the anchor points.

Door blown open and the shed damaged from inside

Cause: Wind pressurising the interior — Fix: Fit a proper hasp and a second bolt at the top or bottom of the door, and make sure the door closes against a stop.

Questions people ask

Is a shed heavy enough to stay put on its own?

A small empty timber shed weighs a few hundred kilograms and generates far more uplift than that in a strong gale. Weight is not a substitute for fixing it down.

Will fixing a shed down affect my insurance?

It is more likely to help than hinder. Some policies exclude storm damage to outbuildings not properly secured, so anchoring it is worth doing on that basis alone.