Siberian larch decking: why it lasts

Among softwoods, Siberian larch (Larix sibirica) is the one buyers reach for when a deck or a cladding job has to survive weather for decades without chemical treatment. It is denser, more resinous and slower-grown than pine or spruce — and that is exactly why it lasts.

Why it lasts

Three things do the work. Density — at 600-700 kg/m³ larch is heavier and harder than most softwoods, so it resists wear and dents. Resin — the wood is rich in natural resins that repel water and discourage rot and insects without preservatives. Slow growth — the short Siberian season produces tight annual rings, which means fewer weak points and better dimensional stability outdoors. Together they put larch in natural durability class 3 (moderately durable), well above untreated pine.

Grades & profiles

Decking is produced to grade and to profile:

• Grades: Prime / AB for a near-knot-free face, BC for a sound knotty look at a lower price.
• Profiles: smooth, or grooved / reeded for slip resistance; square or eased edges.
• Sizes: typically 27 mm thick, 115-143 mm wide, in 3-6 m lengths; cladding runs thinner.

Installation & care

Larch moves with the seasons, so detail it to breathe: ventilate the underside, leave drainage gaps, and use stainless or coated fixings (the resin and tannins can react with cheap steel). Left bare, larch silvers to an even grey patina; oiled, it keeps its warm honey-to-amber tone. Either is a finish choice, not a durability one.

How it compares

Against untreated pine or spruce, larch lasts far longer outdoors. Against thermally modified wood, larch is cheaper and needs no heat process, though thermowood is more stable. Against tropical hardwoods, larch is lighter on the wallet and on the planet — a temperate, replanted species rather than a rainforest one. For most residential and commercial decking, it is the value sweet spot.