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.
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.
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.
Standards
European and international references applicable.
Physical properties
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.