Not all decking boards are the same. Thickness, width, length, grade, and profile all affect how a finished deck looks, performs, and lasts. This guide covers Snowdon Timber's best-selling treated decking boards — what makes each one different, and which projects each one suits best.
All boards in this guide are pressure treated for long-term outdoor use in the UK climate.
What makes a good decking board?
Before choosing a board, three things matter most: thickness, width, and grade. Thickness affects rigidity and load-bearing capacity — a 28mm board is considerably stiffer underfoot than a 21mm board over the same joist spacing. Width affects coverage and the visual rhythm of the finished deck — wider boards mean fewer visible joints. Grade affects appearance, not structural performance — reject-grade boards are structurally identical to premium stock but carry natural characteristics such as knots and colour variation.
Treatment class matters too. All Snowdon Timber decking boards are UC3 pressure treated, meaning they are certified for exterior use above ground in the UK climate. This is the minimum specification for any outdoor deck.
Snowdon Timber's top selling decking boards
Our best-selling board and the most popular choice for residential garden decking. At 25mm thick and 120mm wide, it strikes the right balance between strength, coverage, and cost. The ribbed top face provides wet-weather grip, making it suitable for patios, steps, and raised decks as well as flat garden surfaces.
This board covers approximately 2.88m² per pack of ten — enough for a compact seating area or balcony in a single order. It is available on snowdontimber.co.uk, Amazon, eBay, and B&Q.
At 3.6 metres — 50% longer than our standard 2.4m boards — this board is built for long deck runs where fewer end joints mean less water ingress, a cleaner finish, and less cutting waste. Ideal for side passages, full-width patios, and walkways.
From our Reject range: cosmetically graded with natural knots and colour variation, but structurally identical to premium stock. At 144mm wide it also covers more per board, reducing both quantity and fixing points.
The most versatile board in the range. One face is ribbed for grip and weather resistance, the other smooth for a sleeker, contemporary finish. You choose which face to install on the day — matching the board to your design without ordering a different product.
Particularly useful for covered decking, garden rooms, and sheltered spaces where the smooth face suits the aesthetic without the grip trade-off an exposed deck would require.
The budget workhorse. Full UC3 pressure treatment, 27mm thickness, and 144mm width — at a lower price point due to cosmetic grading. Knots, resin pockets, and colour variation are present but do not affect outdoor performance.
For large projects, this board delivers the same weather resistance and service life as premium stock at a reduced cost per board. It is also the most popular choice for painted decks, where surface characteristics disappear entirely beneath primer and topcoat.
What is reject-grade decking?
Reject-grade decking boards are pressure-treated softwood boards that carry cosmetic imperfections — knots, resin pockets, minor colour variation — that prevent them from meeting premium grade standards. Structurally, they are identical. The treatment class is the same. The timber species is the same. The service life is the same.
For painted decks the distinction is irrelevant — surface characteristics disappear under primer and paint. For natural or stained finishes, the knots and variation of reject-grade boards add character rather than detracting from the finish. For budget-conscious projects, reject-grade boards represent the most cost-effective way to build a durable, properly treated outdoor deck.
Do all Snowdon Timber decking boards come pressure treated?
Yes. Every decking board supplied by Snowdon Timber is UC3 pressure treated as standard. UC3 is the treatment classification for timber used in exterior applications above ground — the correct and minimum specification for any outdoor deck in the UK. Treatment is applied under pressure to penetrate the wood structure rather than coat the surface, which means protection is maintained even where boards are cut or trimmed on site.
Frequently asked questions
What is the most popular decking board size in the UK?
The 25 × 120 × 2400mm pressure-treated decking board is the most widely used specification for residential garden decking in the UK. It provides a good balance of strength, coverage, and cost and is suitable for the majority of standard garden deck projects.
What is the difference between 25mm and 28mm decking boards?
The 28mm board is 3mm thicker, providing greater rigidity underfoot and more resistance to warping and movement over time. For standard residential decking over correctly spaced joists, 25mm is sufficient. For commercial use, heavy foot traffic, or long joist spans, 28mm is the correct specification.
What does UC3 treated mean for decking boards?
UC3 is the European hazard class designation for timber used in exterior applications above ground. UC3 treated decking boards have been pressure treated to resist rot, fungal decay, and insect attack in exposed outdoor conditions. All Snowdon Timber decking boards are supplied UC3 treated as standard.
Are reject-grade decking boards structurally sound?
Yes. Reject-grade decking boards are graded on visual appearance only. They are structurally sound, fully UC3 pressure treated, and perform identically to premium-grade boards in exterior use. The cosmetic characteristics — knots, colour variation, minor surface irregularities — do not affect weather resistance, load-bearing capacity, or service life.
What is the best decking board for a painted deck?
Reject-grade boards are the recommended specification for painted decks. Paint covers all surface characteristics completely, making the finished result visually identical to a painted premium board — at a lower material cost.
Does Snowdon Timber deliver decking boards across the UK?
Yes. Snowdon Timber supplies treated decking boards for delivery across the UK, or available for collection from our timber yards in Bangor and Mochdre, North Wales. Boards are also available through Amazon, eBay, and B&Q.
Snowdon Timber's best-selling decking boards cover every residential and commercial specification — from the 25 × 120mm reject board for standard garden decking, to the 28mm heavy-duty board for high-traffic use, to the 3.6m reject board for long runs with minimal joints. All are UC3 pressure treated and available for fast UK delivery.
