Composite decking in full sun: heat, fade, warping and which colours cope

A south-facing garden is the best place for a deck and the hardest place for a decking board. Full afternoon sun brings three worries with composite: will it get too hot to walk on, will it fade, and will a cheaper board warp or buckle over the years. This guide answers all three for a British garden, says which colours cope best, and gives the build details that stop heat becoming a problem.

The short answer

In full UK sun a composite board gets warmer than timber and, in a dark colour on a hot afternoon, can be uncomfortable barefoot for a handful of days a year. It lightens by about one shade in its first summer and then holds; it does not keep fading. It will not warp or buckle if it is clipped rather than screwed and laid with the right expansion gaps, because the gaps are what let the board move with the temperature. Choose a mid or light colour, fit it to the guide, and a south-facing composite deck lasts 25 years.

Heat: how hot, and what to do

Composite is denser than timber and absorbs more of the sun's energy, so on a still 28°C afternoon a black or chocolate board in direct sun can reach 50 to 60°C at the surface, hot enough that you would not stand on it in bare feet for long. A grey, ash or silver board in the same spot runs 10 to 15°C cooler. Timber runs cooler still, and stone patios run hotter than any of them.

In practice this is a few days each summer in most of the UK, and the fixes are simple: hose the deck for ten seconds and it is cool for an hour; put the seating under a parasol, pergola or sail; and choose a lighter colour if the deck is south-facing with no shade at all. A lawn of artificial grass next to the deck gets warm in the same way, and the same hose sorts both.

Fade: what happens and when it stops

Every composite board lightens in its first three to six months outdoors as surface tannins in the wood fibre wash out and the top layer weathers. Darker boards show it more: black settles to charcoal, chocolate to a warm brown, teak to a softer orange-brown. Grey, silver and ash barely change. After that first season the colour is stable for the life of the board, and that stability is what the ten-year warranty covers. Buy for the settled colour rather than the day-one colour; if you are torn between two shades, choose the darker. The fade guide has a colour-by-colour table.

Warping and buckling: why it happens and how to prevent it

Composite expands and contracts with temperature more than timber does. A 4.8m board grows a few millimetres between a frosty morning and a hot afternoon. If the board is trapped, screwed through its face or butted hard against a wall or the next board, that growth has nowhere to go and the board lifts, bows or buckles. That is the "warping" people see on cheap decks, and it is a fitting fault, not a material one.

• Hidden clips, never face screws. The clip holds the board down and lets it slide lengthways.
• End gaps by temperature on the day you fit: 9mm below 4°C, 6mm between 4 and 24°C, 3mm at 25°C or above.
• 20mm from any wall or fixed edge.
• Joists at 350mm centres so the board cannot sag between supports; 300mm for diagonal boards.
• Store boards flat and covered before fitting; a board left in the sun on uneven ground bows before it is laid.

All of these are in the installation guide, and a deck built to them does not warp.

Which colours cope best in full sun

Colour	Surface heat	First-summer shift	Verdict for a south-facing deck
Ash, silver	Coolest	Minimal	Best choice; shows dirt more than darker boards
Grey	Cool	Minimal	The all-rounder; our most popular for open decks
Oak, teak	Medium	Noticeable, then stable	Good with a parasol over the seating
Red brown, chocolate	Warm	One shade lighter	Fine with some shade; hot barefoot at midday
Black	Hottest	Black to charcoal	Looks superb; keep it for shaded or north-facing decks

Our boards are the same price in every colour, so the choice is about the garden, not the budget. Free samples left in the sun for a week tell you more than any table.

Cheap board or premium: does sun change the answer?

Capped boards, at two to three times the price, fade less in the first months and resist stains better. They get just as hot, and they warp just as readily if face-screwed. For a south-facing showpiece you will own for decades and want to look identical in year fifteen, capping is worth considering. For a family garden, an uncapped board in a mid tone, fitted properly, gives the same 25 years. The types guide sets out what the premium buys.

Checklist for a deck in full sun

1. Grey, ash, silver or oak rather than black or chocolate.
2. Clips, not screws; expansion gaps by temperature; 20mm from walls.
3. Some shade over where people sit.
4. Expect the first-summer colour shift and buy for the settled shade.
5. Rot-proof frame with 40mm of airflow, so the deck under the sun stays dry and stable.