Description

Spruce and Larch are the pulsing arteries of mountain and Scandinavian timber construction. They share the same botanical family (Pinaceae) but differ radically in hygroscopic and structural behaviour, dictating strict rules on which to use indoors and which outdoors.

01Norway Spruce: The Hidden King

Norway Spruce is the world's most-used timber for glulam structures and CLT/XLAM panels. Its main advantage is lightness (about 450 kg/m3) combined with high bending strength. Its Achilles heel is poor natural durability (Class 4). Spruce lacks tannin-based protective resins: if exposed to weather without continuous impregnation, moisture triggers rapid fungal decay. It must always be used under cover.

02Larch: The External Shield

Alpine Larch grows slowly in cold climates, producing very tight growth rings yielding high density (up to 600 kg/m3). The heartwood is saturated with natural resins and tannins acting as a natural preservative. Used as open-jointed ventilated cladding without any varnish, larch resists driving rain for decades. Under UV, tannins oxidise creating a silver-grey patina that further seals the wood.

Technical identity

Standards

European and international references applicable.

EN 338 (Classi di resistenza C14-C50)EN 14080 (Legname lamellare incollato GL)EN 1995 (Eurocodice 5 – Strutture in legno)

Physical properties

Strength class (Solid)C24 (EN 338)
Charring rate (fire)~ 0.7 mm/min (REI60 raggiungibile)
Shear strength (torsion)2.5 N/mm2 (C24)
Critical rot moisture> 20 % (Abete vulnerabile; Larice > 30%)

Usage environment

SPRUCE INDOORS ONLY: solid or glulam spruce must always be protected from rainwater. Use external cladding or render systems. LARCH ON FACADES: with adequate ventilation (min. 40mm cavity) bare larch lasts 30-40 years maintenance-free. Avoid cup joints (collect water). RESIN: larch resin pockets may bleed in summer heat.

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