Non-slip decking: what actually keeps a deck safe in the wet

A deck that is fine in July can be treacherous in November. If you have ever stepped out onto green, greasy boards on a damp morning, you will know why people search for non-slip decking. The good news is that grip is mostly about choices you make once, plus a little routine care.

Why decks get slippery

Three things cause almost all slippery decks:

1. Algae and moss. A thin green film forms on any surface that stays damp and shaded. It is the main culprit, and it grows fastest in autumn and winter.
2. Wet leaves and debris. Leaves trapped in grooves and against walls hold water and rot into slime.
3. Smooth or worn surfaces. Timber that has been jet-washed too often, or boards with a shiny finish, have little texture left to grip.

Notice that only the third is about the boards themselves. A deck in a sunny, breezy spot rarely gets slippery whatever it is made of. One in the shadow of a house or a wall, which describes a lot of yards and sloping gardens, needs more thought.

Grooved boards are not non-slip

Many people assume the ridges on traditional timber decking are there for grip. They mostly are not. Grooves were originally a way of reducing cupping in the board. In use, they hold water, dirt and algae, and can be more slippery than a smooth board once they are green.

If you want grip on timber, look for boards sold as anti-slip, which have resin-and-grit strips set into the surface, rather than relying on grooves.

Composite and grip

Capped composite boards have a hard polymer shell over a core of wood fibre and plastic. That shell does not soak up water, so algae finds it harder to take hold, and a quick wash removes what does. Most capped boards have a textured, wood-grain finish that keeps more grip in the wet than smooth timber.

A few points to check when choosing boards:

• A textured surface. Deep, irregular grain gives better grip than a smooth or lightly brushed finish.
• Capped rather than uncapped. Older, uncapped composite boards can hold water and stain, and some became slippery as they aged.
• The maker’s slip test result. Many manufacturers publish a pendulum test value for their boards, wet and dry. Higher is better; a wet value of 36 or more is generally treated as low slip potential.
• Colour in full sun. Very dark boards get hot in summer, which matters if you walk on them barefoot. It does not affect grip but is worth knowing.

Anti-slip strips and inserts

For an existing timber deck that is slippery, there are retrofit options:

• Anti-slip inserts. Narrow strips of grit-faced resin pushed into the grooves of grooved boards. They are neat and effective, especially on steps.
• Screw-down strips. Aluminium or composite strips with a gritted surface, fixed across the boards. Good on step nosings and ramps, less attractive across a whole deck.
• Anti-slip paints and coatings. Fine-grit coatings can work for a few seasons, but wear through in walkways and need recoating.

Steps deserve the most attention. Falls on decks most often happen on the edge of a step, where a wet foot lands at an angle. A gritted nosing on each tread, and a light so the edges can be seen at dusk, are worth doing on any deck.

Design choices that help

Some of the best protection against a slippery deck comes before it is built:

• Let the sun in. Where you have a choice, put the main deck where it gets sun for part of the day.
• Keep air moving underneath. Leave gaps around the edges so the underside dries out. Decks boxed in tight against walls and soil stay damp.
• Gaps between boards. Correct spacing lets water drain through instead of sitting on top.
• A slight fall. A very small fall away from the house, along the boards, helps water run off.
• Handrails on steps. A rail gives a hand-hold on longer flights, which matters most when the steps are wet. On raised edges, government guidance on guarding (Approved Document K) is the usual benchmark.

Keeping a deck non-slip

Whatever the boards, a simple routine keeps grip all year:

• Sweep regularly, especially in autumn, and clear leaves out of corners and from under planters.
• Wash twice a year, in spring and autumn, with warm soapy water and a stiff-bristled brush, working along the boards.
• Treat algae early. On timber, a deck cleaner made for the purpose helps. On composite, check the maker’s guidance before using any chemical, as some are not suitable.
• Be careful with pressure washers. On timber they raise the grain and wear the surface, which makes it more slippery over time. Most composite makers allow a low-pressure wash with a fan nozzle held well back.
• Lift rubber-backed mats. They trap water and can mark composite boards.

Is composite decking worth it for grip alone?

If your deck will be in shade for much of the day, in a damp area, or used by small children or older relatives, then yes, the grip and low upkeep of textured capped composite are a big part of what you are paying for. In a hot, open, sunny garden, a well-kept timber deck with anti-slip boards can be just as safe.

Our pages on decking for family gardens and decking for small gardens cover the situations where grip matters most, and our decking steps guide covers safe step sizes.