- What it is: Larix sibirica — naturally Durability Class 3, no preservative treatment required for above-ground decking use throughout its 20–30 year service life.
- Profiles available: Smooth 28x140mm, ribbed 27x142mm, grooved 28x140mm, narrow smooth 28x90mm — all from UK stock.
- Cost: £45–£75 per m² depending on profile and grade. Total 15m² deck materials approximately £800–£1,300.
- Maintenance: None required for durability. Optional oiling every 2–3 years to maintain warm gold colour — if you prefer the natural silver-grey weathering, never oil it.
- vs ThermoWood: Larch is slightly more affordable and has warmer natural colour. ThermoWood lasts marginally longer (25–40 yrs vs 20–30 yrs) and has better dimensional stability. Both are strong specifications.
- Tannin note: Larch contains natural tannins that leach as run-off in the first year — protect adjacent light-coloured paving or render during initial weathering.
Siberian larch is one of the strongest natural timber decking specifications available in the UK — naturally durable without any preservative treatment, visually warm and characterful, and capable of lasting 20–30 years above ground with minimal maintenance. It is the naturally durable alternative to ThermoWood: slightly more affordable, with a richer visible grain and natural knot character, and the same zero-chemical treatment philosophy. This complete buyers guide covers everything you need to know about Siberian larch decking in the UK — species characteristics, all available profiles and sizes, costs, installation, maintenance, and how it compares to ThermoWood and treated softwood.
Siberian larch decking boards — the warm honey-gold colour and characteristic grain of freshly machined larch. Kiln dried and FSC/PEFC certified, available from UK stock with nationwide delivery in 7–14 days. All boards are Durability Class 3 — no preservative treatment required throughout the 20–30 year service life.
Why Choose Siberian Larch for Decking?
Siberian larch (Larix sibirica) grows in the extreme conditions of Siberia and northern Russia — long cold winters and short summers. This slow, dense growth produces a timber with one of the highest resin contents of any softwood, tight growth rings, and a natural durability that significantly outperforms standard European softwoods. The result is a timber that achieves Durability Class 3 (Moderately Durable) under BS EN 350 — meaning it is suitable for above-ground exterior use throughout its service life without preservative treatment.
For UK garden decking, Siberian larch offers three distinct advantages over standard treated softwood: no chemical treatment obligation throughout its life, a naturally warm and characterful appearance with visible grain and knot detail, and a service life (20–30 years) that significantly exceeds treated pine (10–15 years with annual oiling). It costs more upfront than treated softwood — but the whole-life cost calculation almost always favours larch when annual oiling and eventual replacement are factored in.
Compared to ThermoWood, larch is slightly more affordable, has a more characterful appearance with visible knot detail, and is naturally durable rather than modified. ThermoWood has a marginally longer service life and better dimensional stability. For most residential UK garden decks, both are excellent — the choice is primarily aesthetic and budget-driven. See our full larch vs ThermoWood decking comparison for the detailed breakdown.
Siberian Larch Decking Profiles — All Options
Smooth 28x140mm
Siberian larch smooth decking 28x140mm — the clean flat face and warm honey-gold grain make this the most popular larch decking profile. Face-fixed with A4 stainless steel decking screws. The wide 140mm board width creates a generous, contemporary deck surface with fewer visible joints.
Standard smooth face-fixed profile. The 28mm depth provides good structural rigidity at 400mm joist centres. Wide 140mm board for a contemporary deck appearance. Fix with A4 stainless decking screws — two per joist per board.
Ribbed 27x142mm
Siberian larch ribbed decking 27x142mm — the machined longitudinal ribs provide enhanced grip in wet conditions, making this profile the recommended choice for family gardens, areas used in all weathers, or any deck where slip resistance is a priority. The ribs also give a distinctive textured appearance distinct from smooth boards.
Machined ribbed face for enhanced slip resistance — the standard recommendation for residential garden decks in the UK. The ribs reduce the effective contact surface that can become slippery when wet. Reversible — smooth face also available underside.
Grooved 28x140mm
Siberian larch grooved decking — the side groove accepts hidden decking fastener clips, producing a completely fixing-free deck face. The grooved surface profile provides enhanced grip in wet conditions — face-fixed with A4 stainless steel decking screws, the same as the smooth and ribbed profiles.
Face-fixed profile with a machined groove running along the board face — similar in function to the ribbed profile, providing enhanced grip and slip resistance while giving a slightly different surface aesthetic. Fix with A4 stainless steel decking screws. A good alternative to ribbed for those who prefer the look of a single central channel rather than multiple ribs. Browse our full fixings range for the correct A4 stainless screws for this profile.
Batten Decking 45x70mm — Contemporary Narrow Board Alternative
Siberian larch batten decking — 45x70mm PAR larch battens laid as deck boards. This contemporary approach uses structural larch battens as the deck surface, creating a clean narrow-board rhythm with defined shadow gaps between each board. A popular specification for contemporary garden rooms and minimalist outdoor spaces.
PAR larch battens used as deck boards — a contemporary design approach that creates a clean narrow-board deck surface with defined shadow gaps between each board. The 45mm depth provides excellent structural rigidity. Fix with A4 stainless steel screws at 400mm joist centres. Increasingly popular for garden rooms, contemporary terraces, and minimalist outdoor spaces where a fine-board rhythm suits the design intent.
How Siberian Larch Decking Weathers
Siberian larch decking weathered to silver-grey — left untreated, larch weathers from warm honey-gold to a rich silver-grey over 12–18 months. The weathered appearance is attractive, structurally harmless, and self-maintaining once established. This is the natural state that most larch deck owners choose — zero maintenance, consistently beautiful.
Left untreated, Siberian larch weathers through a UV-driven photochemical process — the surface lignin breaks down and the colour transitions from warm honey-gold through golden-brown to a rich silver-grey over approximately 12–18 months. The weathered appearance is one of the defining characteristics of a natural larch deck — distinctive, attractive, and self-maintaining once established.
The greying is purely cosmetic — it does not affect the timber's Durability Class 3 rating or its 20–30 year service life. The grey surface layer is a photochemical change, not biological decay. A larch deck that has been weathered silver-grey for 10 years is structurally identical to one installed recently — the same natural durability throughout.
If you want to maintain the warm gold colour, apply Koopmans Houtolie wood oil before installation and every 2–3 years thereafter. This significantly slows the greying process. For the full cleaning and maintenance approach, see our timber decking cleaning guide.
Siberian larch contains natural tannins that leach from the surface during the first 12–18 months of weathering as rain washes over fresh boards. This run-off can cause brown staining on adjacent light-coloured paving, render, or masonry. Protect vulnerable adjacent surfaces with sealant or temporary covering during the initial weathering period. Once the tannins have largely leached out — typically after the first full weathering season — run-off staining reduces significantly.
Installation — Key Points
- Joist spacing: Maximum 400mm centres for 28mm boards. Use C16 pressure treated or naturally durable timber joists — never untreated softwood joists which will fail well before the larch boards above them
- Air gap: Minimum 50mm clear air gap between the bottom of the joists and the ground below — essential for ventilation and preventing moisture accumulation beneath the structure
- Fixings: A4 stainless steel decking screws throughout — never galvanised. Larch's natural tannin content reacts with galvanised fixings, causing accelerated corrosion and blue-black staining around each fixing point. Two screws per joist per board, pre-drilled within 50mm of board ends
- Board orientation: Heart side down — boards cup away from the heart side as they dry, so heart-side-down boards curve upward at the edges (draining) rather than downward (pooling)
- Expansion gaps: Leave 5–6mm gaps between boards to allow for seasonal movement. Larch's Class 3 durability does not eliminate moisture-related movement — maintain consistent gaps using spacers
- End grain sealing: Seal all cut ends on site with exterior wood oil or end grain sealer immediately after sawing. Larch's end grain absorbs moisture significantly faster than face grain
Siberian Larch vs the Alternatives
| Species | Service life | Maintenance | Cost/m² | Character |
|---|---|---|---|---|
| Siberian Larch | 20–30 yrs | None required | £45–£75 | Warm grain, visible knots, silver-grey patina |
| ThermoWood | 25–40 yrs | Zero — ever | £55–£80 | Rich honey-brown, finer grain, silver-grey patina |
| Pressure Treated Softwood | 10–15 yrs | Oil annually | £15–£30 | Light green tint, standard grain |
| Composite decking | 15–25 yrs | Annual clean | £60–£120 | Consistent colour, wood-effect pattern |
Siberian larch decking is the strongest choice for homeowners who want a naturally durable, characterful deck that requires no treatment obligation and weathers beautifully — at a lower upfront cost than ThermoWood. The visible grain, natural knot character, and warm gold-to-silver weathering patina make larch the most visually interesting of all the natural timber decking options. If you want something that looks unmistakably natural and ages with character, larch is the specification. If maximum service life and absolute dimensional stability are the priority, ThermoWood has the edge. For a full guide on building your deck, see our how to build a deck UK guide.
How long does Siberian larch decking last in the UK?
Siberian larch decking lasts 20–30 years above ground in UK conditions — no preservative treatment required. Correctly installed with a ventilated subframe, A4 stainless fixings, and 50mm+ air gap below the boards, 25 years is a realistic expectation for most UK locations.
Does Siberian larch decking need treating?
No — Siberian larch is Durability Class 3 and needs no preservative treatment above ground. Oiling every 2–3 years is optional for colour maintenance only. If you are happy with natural silver-grey weathering, no treatment is ever needed throughout the 20–30 year service life.
How much does Siberian larch decking cost in the UK?
Siberian larch decking costs £45–£75 per m² for boards. Add £8–£12 per m² for fixings and hardware. A 15m² deck requires approximately £800–£1,300 in materials. Professional installation adds £600–£900 for a standard ground-level deck.
Is Siberian larch decking better than ThermoWood?
Both are excellent. Larch is slightly cheaper, more characterful in appearance, and naturally durable. ThermoWood lasts slightly longer (25–40 years vs 20–30 years) and has better dimensional stability. For most UK residential decks both are strong — the choice is usually aesthetic and budget-driven.
Will Siberian larch decking go grey?
Yes — left untreated, larch weathers to silver-grey over 12–18 months. This is purely cosmetic and does not affect durability. The weathered look is attractive and self-maintaining. Oil every 2–3 years with Koopmans Houtolie to slow the greying and maintain the warm gold colour.
Siberian Larch Decking — All Profiles from UK Stock
We supply Siberian larch decking in smooth, ribbed, grooved and narrow profiles from UK stock. Standard and premium grades available. FSC and PEFC certified. Nationwide delivery in 7–14 days. Contact our team with your deck dimensions for a precise quantity and quote.