Softwood Decking

Softwood decking refers to deck boards manufactured from coniferous, fast-growing tree species rather than the slower-growing broadleaf trees that produce hardwood timber. In the UK, the most commonly used softwood species for decking are pine, spruce, larch, and redwood — all of which offer a good combination of workability, availability, and cost-effectiveness. Despite the name, softwood does not mean structurally weak; many softwood species used for decking are robust enough for decades of outdoor use when correctly treated and maintained. The majority of softwood decking sold in the UK is pressure-treated with a preservative solution before sale, which significantly improves its natural resistance to rot, fungal decay, and insect attack. Boards are typically available in grooved or smooth profiles, with grooved boards providing some additional texture underfoot. Larch is often cited as one of the best-performing softwood species for outdoor use, as it is denser and more naturally durable than pine or spruce. Softwood decking is the most affordable and widely available decking material on the UK market, making it the most popular choice for residential garden deck projects — particularly where budget is a primary consideration or the deck is intended for a shorter-term installation.

The lifespan of softwood decking depends primarily on the quality of the timber, the standard of pressure treatment it has received, how well it is installed, and how consistently it is maintained over time. Poorly maintained or untreated softwood can begin to deteriorate within 3 to 5 years, particularly in damp, shaded conditions where moisture and fungal growth are more active. Good quality pressure-treated softwood decking, correctly installed with adequate ventilation beneath the boards and regular treatment applied, can realistically last between 15 and 25 years. Look for boards carrying the DeckMark quality mark from the Timber Decking and Cladding Association, or products backed by a manufacturer warranty of at least 15 years against fungal decay and insect attack — as a rule of thumb, a 15-year warranty typically indicates a 20-year service life in normal residential use. Key factors that shorten the lifespan of softwood decking include boards sitting in direct contact with soil or pooled water, inadequate gaps between boards restricting drainage, infrequent cleaning allowing algae and moisture to accumulate, and failure to treat cut ends with a brush-applied end grain preservative after installation. With the right materials, installation approach, and a simple annual maintenance routine, softwood decking represents excellent value and will serve well for many years.

Softwood decking boards are the most affordable decking material available in the UK, with prices for pressure-treated boards typically ranging from £20 to £45 per square metre for materials alone, depending on the species, board width, profile, and supplier. Standard pressure-treated pine and spruce boards sit at the lower end of this range, while higher-specification larch or redwood boards with a better durability profile command slightly more. These board costs do not include the timber subframe, fixings, decking stain or oil, or any gravel or weed membrane laid beneath the deck before installation. For a professionally installed softwood deck including all materials, subframe, and labour, expect to pay between £70 and £100 per square metre in most parts of the UK, with costs at the higher end in London and the South East. A typical 20-square-metre garden deck in softwood would cost between £1,400 and £2,000 fully installed, making it by far the most budget-friendly decking option available. A DIY softwood deck installation can reduce costs significantly further, as softwood is easy to cut and work with using standard tools, and the boards do not require pre-drilling or specialist fixings. When comparing prices, always check that like-for-like board dimensions and treatment specifications are being quoted, as significant variation exists between product grades.

Most softwood decking sold in the UK arrives pre-treated with a factory-applied pressure treatment preservative, which is forced deep into the timber fibres under pressure to protect against rot, fungal decay, and insect attack. This pre-treatment is essential for outdoor use and forms the foundation of the board's durability — softwood used outdoors without any preservative treatment will deteriorate rapidly in the UK climate. However, there are two important additional treatment steps that should always be carried out at the point of installation regardless of whether the boards are pre-treated. First, every cut end, notch, or large borehole made during installation must be treated on site with a brush-applied end grain preservative, as the cutting process exposes untreated timber that is highly vulnerable to moisture ingress and rot. Failing to treat cut ends is one of the most common causes of premature deterioration in otherwise well-installed decks. Second, once the boards have been laid and have had time to dry and settle — typically after allowing six months of weathering — an application of a good quality decking stain, oil, or sealant should be applied to the surface and sides of the boards to provide UV protection, enhance water resistance, and maintain the appearance of the timber. This surface treatment should then be refreshed annually or every two years depending on wear and exposure.

Whether to leave a gap between softwood decking boards during installation depends on the moisture content of the boards at the time of laying, and getting this right is important for both the appearance and the long-term performance of the deck. Freshly pressure-treated softwood boards typically have a high moisture content — often 20% or above — because water is used as part of the treatment process. These wet boards will shrink as they dry out after installation, meaning they should be butted tightly together when fixed, as adequate drainage gaps will naturally open up as the timber dries over the following weeks and months. Boards that have been kiln-dried after treatment (sometimes labelled KDAT) have had most of their moisture removed before delivery, and these should be installed with a gap of approximately 5 to 6mm between boards to allow for the slight expansion that will occur when the timber absorbs moisture in wet weather. The Timber Decking and Cladding Association recommends leaving adequate spacing between all boards to allow surface water to drain through, prevent debris from accumulating, and accommodate the natural seasonal movement of the timber. Regardless of gap size, always leave a minimum 10mm gap where boards abut a wall or building to allow airflow and prevent moisture build-up against the structure.

Warping and cupping are common issues with softwood decking and are almost always linked to moisture — either excessive moisture absorption, uneven drying across the board, or inadequate fixings that allow the timber to move freely. Cupping, where the edges of a board rise higher than the centre, typically occurs when the top face of the board dries out faster than the underside, causing differential shrinkage across the width. This is particularly common where ventilation beneath the deck is poor and the underside of boards stays persistently damp. Warping along the length of a board usually indicates that the timber had a high moisture content when installed, that the grain is not straight, or that the board includes the central pith of the tree — which is the most dimensionally unstable part of the timber. To minimise the risk of warping, always select boards with straight grain and narrow growth rings visible at the end, and check that the board does not already show signs of curve or twist before buying. Fixing boards at every joist rather than skipping fixings will help keep boards flat as they dry. Applying a good quality decking stain or oil to all faces of the boards — including the underside before laying — creates a more even moisture barrier and significantly reduces the rate of differential drying that causes cupping. Boards that have already warped significantly may need to be replaced, though minor cupping can sometimes be corrected by reapplying fixings while the timber is damp and more pliable.

Staining or painting softwood decking is one of the most effective ways to protect the timber from weathering, moisture damage, and UV fading, as well as refreshing its appearance and colour. Before applying any product, the deck must be thoroughly cleaned to remove dirt, algae, and any existing loose or flaking treatment. A specialist decking cleaner applied with a stiff brush, followed by a rinse and a full drying period of at least 24 to 48 hours, will prepare the surface correctly. New pressure-treated softwood boards should be left to weather for approximately six months before the first stain or oil is applied, allowing the factory treatment to erode sufficiently for the new product to penetrate and adhere effectively. Decking stain should be applied on a dry day with temperatures above 10°C, working in the direction of the grain using a brush or roller across three to four boards at a time to avoid overlap marks. Two coats are generally recommended for new or recently cleaned timber, with the second coat applied after the first has had the time specified on the product to penetrate — typically three to four hours. Unlike surface-coating paints, penetrating decking stains and oils do not peel or flake, making them easier to maintain over time as additional coats can be applied directly without stripping the previous application. A maintenance coat of stain should be applied every one to two years to maintain protection, with the frequency depending on wear, sun exposure, and the product used.

Using the correct fixings for softwood decking is important both for the structural integrity of the deck and to avoid staining or premature deterioration of the boards. All fixings used with pressure-treated softwood must be manufactured from corrosion-resistant materials — stainless steel, hot-dipped galvanised steel, or specialist coated screws are the appropriate choices. Standard bright zinc-plated or ordinary steel fixings will corrode rapidly when in contact with the preservative chemicals used in pressure-treated timber, leading to rust staining on the board surface and eventual failure of the fixing itself. Screws are strongly preferred over nails for softwood decking as they provide a much more secure hold, are less likely to work loose over time as the timber moves seasonally, and can be removed cleanly if a board needs to be replaced. The fixings should be at least two and a half times the thickness of the board being fixed — for a standard 28mm decking board, this means a minimum screw length of 70mm. Each board should be fixed at every joist crossing rather than at alternate joists, as more frequent fixings help keep the boards flat and reduce the effects of seasonal movement. Always pre-drill countersunk pilot holes in softwood boards before driving screws to prevent the board face from splitting, and countersink fixings slightly below the surface to avoid creating trip hazards and to reduce water collection around the fixing point.

Softwood decking can be used in shaded or north-facing gardens, but it requires more frequent maintenance and careful installation to perform well in these conditions, as persistently damp and shaded environments significantly accelerate the growth of algae, moss, and mould on the board surface. Unlike south-facing decks that benefit from sun exposure to help the boards dry out after rain, shaded decks stay damp for longer, creating ideal conditions for organic growth that makes the surface slippery and promotes timber deterioration over time. If installing softwood decking in a shaded location, choosing a grooved board profile will help channel surface water away from the deck more effectively. Ensuring the subframe allows maximum airflow beneath the boards is equally important — a well-ventilated underside dries out far more quickly than one that traps moisture. Cleaning the deck more frequently than in a sunny location — at least three times per year rather than twice — with a specialist decking cleaner to remove algae and moss will be necessary to maintain both appearance and safety. Applying a decking treatment product that incorporates a biocide or mould inhibitor will provide additional protection against the organic growth that is more prevalent in shaded gardens. For a deck that will spend most of its life in shade and receives minimal sun exposure, composite decking or a denser hardwood species are worth considering as they are more inherently resistant to the conditions that make softwood management more demanding in these environments.

Yes, pressure-treated softwood is the standard and most widely used material for constructing the subframe — the joists, beams, and posts that form the structural foundation of any timber deck. However, the specification of the pressure treatment required for structural subframe timbers is higher than that needed for the deck boards above ground. The Timber Decking and Cladding Association recommends that all deck joists, posts, and beams should be preservative pressure-treated to Use Class 4, regardless of whether they are in direct ground contact or not, to ensure the structural integrity and safety of the deck over its full service life. Use Class 4 treatment provides a higher loading of preservative than the Use Class 3 standard typically applied to decking boards, and is essential where timbers are closer to the ground, in contact with concrete, or in areas of restricted airflow where moisture levels are persistently higher. Whitewood, a common and inexpensive softwood, is not recommended for subframe use without special treatment such as incising, as it does not absorb preservative penetration as readily as other softwood species. For posts set directly into the ground, the timber must be rated for ground contact use. All cross-cuts, notches, and holes made during subframe assembly should be treated on site with a brush-applied end grain preservative before assembly to maintain the integrity of the treatment at every cut surface.