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Most winter damage to a composite deck starts in October, not January. Wet leaves sit in the gaps, water stops draining, and a freeze then locks it all in place.

The fix is a short autumn routine. Clear the leaves, open every drainage gap, check underneath, and decide now how you'll deal with snow. This guide walks you through each job in order.

It's also written around our warranty terms. Some popular winter tips can void your cover, and we'll point those out as we go.

Why does autumn matter more than winter itself?

Composite boards cope well with cold and rain. The trouble comes from what sits on top of them.

Fallen leaves release tannins as they rot. On a deck, that shows up as brown marks, and uncapped boards mark more easily than capped ones. Damp leaf piles also feed algae, which makes the surface slippery.

Leaves and grit also pack into the gaps between boards. Once those gaps block, water sits on the surface and under the deck. Repeated freezing and thawing then works on the boards and the frame below.

So the aim in autumn is simple. Keep the surface clear and keep water moving.

Your autumn checklist at a glance

Clear the leaves every week

A soft or stiff broom works well, and so does a leaf blower. Avoid metal rakes, as the tines can scratch the surface.

Don't leave the piles beside the deck. Bag them or turn them into compost. The RHS has a simple guide on how to make leafmould from autumn leaves, which gives you free mulch for the borders next year.

Open up every drainage gap

Walk the deck and look along each gap. A flat scraper or a thin plastic tool will lift out packed leaves and grit. Then run a hose across the boards and watch where water sits.

If the same spot holds water every time, look for the cause. A board may have moved, or the frame below may have dropped slightly. Clearing the puddle each week won't fix that.

Check underneath the deck

This is the job most people skip. If you can reach the subframe, look for soft or dark patches on timber joists and any fixings that have worked loose.

Make sure air can still move under the deck. Leaves often build up along the edges and block ventilation. A damp, airless void is bad for any timber frame.

Our installation guide asks for a double joist at every butt joint. If yours were added later and you're not sure, now is a good time to check. Our warranty doesn't cover movement caused by an inadequate subframe, poor drainage or poor ventilation.

Found something you can't fix yourself? Take photos and contact us before lifting any boards. Removing boards before we've assessed a problem can affect a warranty claim.

Move planters, mats and furniture

Anything that sits in one place all winter traps moisture underneath. Lift planters onto pot feet and move furniture off the boards if you can.

Take up rubber-backed mats too. Our warranty specifically excludes staining from rubber mats and planters, so this one is worth doing.

Give it one proper wash

Wash the deck once before the frosts arrive. Use warm soapy water and a soft-bristled brush, working along the boards. Rinse well with clean water afterwards.

Skip bleach and solvent-based cleaners. Both are excluded under our warranty. Abrasive pads and wire brushes are out too. Don't sand capped boards at any time of year, as you'll remove the protective cap.

For the full year-round routine, including stain removal, see our guide on how to maintain composite decking.

Check clips, screws and trims

Press each board with your foot as you walk the deck. A board that rocks or clicks may have a clip out of place. Edge trims can also lift at the corners.

Small fixes now are quicker than loose boards in February. Spare hidden fixing clips, starter clips, colour-coded screws and matching trims are all in our composite decking accessories range.

One thing not to fix: wider gaps at the board ends in cold weather. Composite boards contract as temperatures drop and expand again when it warms up. Those gaps are doing their job.

How should you deal with snow and ice?

Use a plastic shovel or a broom to clear snow. Push along the length of the boards rather than across them. Never use a metal shovel, scraper or ice chipper.

Don't use rock salt or chemical de-icers. Our warranty rules them out, and they can leave marks on the surface. You may see calcium chloride recommended elsewhere, including in older advice. We'd still avoid it on our boards.

Pay extra attention to steps and shady corners. These stay damp longest, so algae builds up there first. Give them a scrub in October even if the rest of the deck looks clean.

The safest approach is to keep algae off and snow cleared. A clean, textured board gives far better grip than one coated in green film. If you need grip on steps during a hard frost, sweep them first and use extra care.

What changes for coastal and poolside decks?

Salt spray and chlorine leave deposits that need regular washing. For these decks, our warranty asks for monthly cleaning with mild soapy water, followed by a fresh-water rinse.

Keep that going through winter. Storms carry more salt inland, and it's easy to let the routine slip when nobody is using the deck.

Did you lay a new deck this summer?

If you ordered composite decking on or after 26 August 2026, check you've registered it. Cover now depends on registration within 90 days of delivery. You'll need your order number, the delivery date, and the range and colour.

If the deck wasn't finished at the time, you still register within the 90 days. Then email us within 30 days of completion with photos of the finished deck. The full terms are on our warranties page.

It takes a few minutes and protects up to 15 years of residential cover on capped boards.

Frequently asked questions

Do I need to cover composite decking in winter?

No. Composite decking is designed to stay outside all year without a cover. Covers can trap moisture and leaves against the boards. Keep the surface clear and the drainage gaps open instead.

Can I use salt on composite decking?

We don't recommend it. Our warranty excludes damage from rock salt and chemical de-icers. Clear snow with a plastic shovel or broom, pushing along the boards, and keep algae off for better grip.

Why are the gaps between my composite boards bigger in winter?

Composite boards contract in cold weather and expand when it warms up. That's why they're laid with expansion gaps. Slightly wider gaps in winter are normal and close again in spring.

How often should I clear leaves from composite decking?

Once a week during autumn is a good rule. Wet leaves left for longer can leave tannin stains, especially on uncapped boards. Check the gaps after windy days, as leaves pack in quickly.