Why are wooden decking boards ideal for sunny days?

Wooden decking is ideal for sunny days, as wood has low thermal conductivity and heats up more gradually than tiles, stone or dark composite materials, making it more comfortable to walk on barefoot. With proper expansion gaps and ventilation from below, the wood behaves predictably through cycles of heat and rain and releases moisture more quickly, preventing a ‘steam room’ effect beneath the decking. Stability in full sun depends on the selection and moisture content of the material (e.g. kiln-dried Scandinavian spruce, well-graded larch) and on the use of suitable, corrosion-resistant fixings.

What makes wooden decking panels the best choice in full sun?

Wooden decking is ideal for sunny days, as it does not heat up as much as stone or dark composite materials, and provides a more natural, consistent level of comfort underfoot.

In practice, this is immediately apparent: in the afternoon, when the terrace faces south or west, the wood gives off heat more gently, and the surface doesn’t get uncomfortably hot when walking barefoot.

At Dąb Gaj Wood, we design and install decking and timber structures so that this comfort does not end after just one season, but remains intact even after three years of sun and rain.

Decking boards perform well in hot weather partly because, when laid correctly, the timber behaves predictably and has a way to release moisture after a storm, rather than building up heat underneath.

If you’d like to see how we select the profile, thickness and finish, take a look at our range: wood panels for a terrace – it’s the finer details of the workmanship that make all the difference in July, not just the colour in the catalogue. In the following sections, I’ll break the topic down into its constituent parts: wood species, OSMO finish, installation and common mistakes that only become apparent after the first heatwaves.

Why is wood on a decking more comfortable underfoot than tiles or composite materials?

Wood feels more comfortable in the sun because it has a lower thermal conductivity than ceramics and concrete, so it releases the heat it has absorbed more slowly to the skin. In practice, this means that even when the boards are warm, there is none of that burning sensation that often occurs on porcelain tiles or dark decking boards.

Furthermore, the texture of the wood (brushed or grooved) breaks up contact, whilst the micropores help to drain away a film of water more quickly after a sudden downpour.

Comfort in hot weather also depends on the colour and finish: light-coloured wood stains and oils with UV filters reflect some of the radiation and stabilise the colour. In practice, a south-facing terrace in a dark colour will always be warmer, regardless of the material, so it is better to incorporate shade into the design from the outset (a pergola, a louvre, or a polycarbonate canopy) rather than relying on the material to do the job.

If the terrace forms part of a larger garden structure, it is worth integrating it into a single design: 18×18 cm support posts for the roof, a main beam and rafters selected to suit the span and snow load, rather than estimated by eye.

The most common mistake that spoils comfort in the sun is laying the boards or panels too tightly together, without leaving expansion gaps. As wood goes through its natural cycle – night-time damp and daytime heat – it changes in width only slightly; however, if there is no gap, it begins to bulge or wedge itself against the screws, resulting in sharp edges.

A well-built terrace has a controlled gap, stable supports and corrosion-resistant fixings, because hot metal coming into contact with moisture is a sure-fire way to get black water stains.

What type of wood and what grade should I choose for wooden decking when the terrace is in full sun?

In full sun, wooden decking panels made from timber with a stable structure and predictable shrinkage perform best, rather than random boards of mixed quality. Scandinavian spruce is a good choice when it is carefully selected, kiln-dried and properly treated with oil, as it has an even grain pattern and is less prone to unexpected behaviour during seasonal changes.

Larch naturally offers greater resistance to weather conditions thanks to its resins, but requires a careful approach to selection – if the timber is of poorer quality, it is more prone to cracking in the sun.

In structures accompanying a terrace (e.g. roofing, pergolas, screening walls), the timber grade is even more important than in the decking itself. KVH is solid structural timber, kiln-dried and joined using micro-finger joints, which offers consistent dimensions and less shrinkage than standard sawn timber – making it ideal for rafters or transoms.

BSH GL24 SI is a laminated timber with a GL24 strength class, which retains its geometry over long spans and is less prone to twisting; in practice, a main beam made of BSH does not sag after two seasons when subjected to the weight of, for example, polycarbonate, metal roof tiles or even clay roof tiles.

If the decking is integrated into a gazebo, carport or pergola, ask the manufacturer not only about the timber grade but also about its moisture content at the time of installation. Material that is too wet after 1 July can release moisture rapidly, resulting in cracks at the edges and gaps widening.

In well-prepared material, the difference after three seasons is plain to see: fewer splinters, less warping and a more stable colour.

How do OSMO oils and wood stains protect a decking from UV rays and overheating in July?

OSMO oils and wood stains protect your decking from the sun because they penetrate the wood fibres rather than forming a hard coating that cracks due to the wood’s natural movement and UV rays. OSMO Oil Extra forms a flexible layer within the wood, meaning the surface does not flake like varnish, and refurbishment after 2–3 seasons usually involves simply washing the surface and applying another coat.

OSMO UV-Schutz-Öl is an oil containing UV filters which slows down greying and stabilises colour on terraces exposed to strong sunlight, particularly on façade walls and cladding panels where UV rays strike at an angle for many hours.

The choice of pigment also has a significant effect in hot weather: the more pigment there is in the oil, the better the UV protection, but also the greater the change in colour compared to untreated wood.

On terraces where people walk barefoot, I avoid using extremely dark colours, as any material will then feel warmer; it is better to choose a medium or light shade and provide structural shade (a pergola, or a rotating terrace awning).

A blind with adjustable slats allows you to set the angle so as to block out the harsh sunlight whilst still letting a breeze through – this is often more important for comfort than the temperature of the slats themselves.

A common mistake when maintaining the deck is to apply oil in direct sunlight on a hot terrace. The oil then dries too quickly, doesn’t have time to soak in evenly and can leave streaks that are only visible when the sun is low and shining at an angle.

The second mistake is applying too thick a layer – the wood should be saturated, not drenched, because excess oil attracts dust and becomes slippery after the first rain.

• If the terrace is used every day in the summer, I check the condition of the oil coating after the first season and usually give the high-traffic areas a light touch-up. These are the areas where UV exposure and wear and tear occur simultaneously.
• If the panels are partially covered (e.g. by bitumen shingles or polycarbonate), I adjust the maintenance routine accordingly: the exposed section ages more quickly, so it makes no sense to stick to a single schedule for the entire surface.

What determines the durability of decking installations in the sun and after summer storms?

Three factors determine the durability of the installation: ventilation from below, the right fixings and stable support, as the terrace is subjected to alternating exposure to sun and rain. If there is no gap or drainage beneath the panels, moisture accumulates against the joists; then, when the heat arrives, it turns into a steamer – this is the quickest route to warping and accelerated wear of the coating.

That is why clearances, the slope away from the building and effective drainage are so important – rather than just a neat joint between the boards.

Fasteners must be selected to suit an outdoor structure, not to match the furniture in the living room. Stainless steel screws or appropriately protected screws, galvanised anchors for the posts and steel fasteners at the structural joints eliminate the problem of black water stains and loosening of connections following heating and cooling cycles.

If the deck is connected to a pergola or a canopy, I lay the point foundations and level the posts (e.g. 18×18 cm) in such a way that water cannot seep back under the structure, because then even the best wood preservative won’t be of any use.

Technically, a terrace does not usually require planning permission, but when a roof or other structure is added, regulations concerning the built-up area and the classification of the structure come into play.

A building notification may be sufficient for simple canopies, whilst for larger structures or those integrated into a building, a planning permission may be required – this is something worth checking before placing an order, so as to avoid having to revise the design partway through.

From a practical point of view, a small detail like this on paper can save the installation deadline, as the structure cannot be sensibly broken down into stages if the foundations and anchors are to be aligned from the outset.

If you want a decking that’s comfortable in July and doesn’t become slippery or collect splinters after a storm, the key lies in the combination of good-quality timber, proper installation and sensible maintenance with oil – not just one ‘magic’ feature from the product description.

In practice, it’s best to discuss your exposure to the sun, the slope of the land and whether you’re planning to provide shade using a pergola or blinds, as these factors determine both the layout of the panels and the choice of finish.

If you want to go through this process – from design to installation – without having to guess what’s going on site, please get in touch with Dąb Gaj Wood and we’ll come up with a solution that will look great in full sunlight for seasons to come.

Read also: Are wooden panels for pergolas suitable for seasonal roofing?

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