Timber vs Composite Decking for Outdoor Floors

How natural timber, thermally modified wood and composite boards differ in sun, moisture and maintenance, and how to build the subframe correctly.

Decking is a comfortable floor for terraces, pool surrounds and garden platforms: it feels warm underfoot, lets rain drain through the gaps and does not need the heavy base that stone paving does. But there is no universal answer to "timber or composite?". Every material has a weak point, and the choice comes down to whether that weakness will show up in the conditions of your garden.

Natural timber: a living material that needs regular care

For outdoor use, naturally oily, dense tropical hardwoods are used, as well as species like pine and larch that are pressure-treated. Timber's strengths are its natural look and feel, and the fact that a damaged board is easy to replace.

Its weak points are sun and moisture. Under UV light timber gradually turns silver-grey; some see that as a handsome patina, others as a defect. If you want to keep the colour, the boards need oiling regularly. As wet and dry periods alternate, timber swells and shrinks, which can lead to splitting and lifting edges.

Thermally modified timber

Thermowood goes through a special high-temperature treatment. As a result it absorbs less moisture, is more dimensionally stable and resists rot better. The colour darkens, although it too can go grey in the sun.

The treatment makes the wood somewhat more brittle. Pre-drilling is recommended for screws near board ends, and areas exposed to knocks need some care.

Composite boards: low maintenance, with their own quirks

Composite decking is made from wood flour or fibre mixed with polymer. In better products the surface is covered with an extra protective cap layer. The main advantages are stable colour, no rot and no oiling; washing with water is usually enough.

Still, composite has characteristics to keep in mind:

• thermal expansion — length changes with temperature, so the end gaps specified by the manufacturer must be left;
• heat in the sun — dark boards can get uncomfortable to walk on barefoot in summer; lighter shades fare better;
• repairs — a damaged board can be replaced, but matching the colour years later can be difficult;
• fixing — usually with hidden clips, and only with the manufacturer's own system.

Hollow (chambered) profiles are lighter and cheaper but more sensitive to impacts and to flexing under load. Solid profiles are heavier and feel more substantial.

The subframe: hidden but decisive

The lifespan of a deck is often determined not by the boards but by the structure beneath them. The most common mistakes are:

• no ventilation under the boards — moisture lingers, timber rots and composite distorts;
• joists spaced wider than the manufacturer allows — boards feel bouncy underfoot;
• joists laid directly on the ground — adjustable pedestals or a concrete base are needed;
• no fall or drainage planned for water;
• fixings that are not stainless on metal parts.

Joists are made of aluminium profiles or specially treated timber. If ordinary timber joists are used under composite boards, the joists fail long before the boards and the whole deck has to come up.

The gap between boards is not arbitrary either. Too narrow and it fills with leaves and dust, water cannot drain and board edges stay damp. Too wide and it catches heels, small objects and pets' paws. With timber, the gap depends on the moisture content at installation: dry boards will swell later, wet ones will shrink.

Slip resistance and pool surrounds

Wet decking can be slippery, whether timber or composite. A grooved surface helps water run off, but if algae and dirt build up in the grooves, slipperiness increases. In shady, damp spots regular cleaning is essential. Around a pool, check the manufacturer's data on resistance to pool water chemicals. Board direction is worth thinking about as well: boards laid across the main line of movement make a space look wider, while boards laid lengthwise emphasise the route.

Questions that help you decide

• Is the terrace in direct sun all day?
• Will people walk barefoot around a pool?
• Are you prepared to oil the deck once or twice a year?
• Which matters more: a natural feel or a stable colour?
• Is there enough height under the deck for ventilation?

Seeing in advance how the deck works with the facade and the interior materials makes the choice much easier. Zaferoğlu İnşaat develops garden and terrace solutions for private houses and villas using computer models; timber and composite boards can be compared side by side on your own terrace there.