The load-bearing skeleton of timber construction. Selected European conifers valued for their exceptional strength-to-weight ratio. Norway Spruce dominates hidden structures and CLT panels for its lightness, while Larch, thanks to its density and natural resins, is the king of weather-exposed facades.
The stability of the board depends on how it was cut relative to the growth rings. Radially sawn (rift-sawn) boards will not warp over time. The heartwood is structurally stronger and more durable than the outer sapwood.
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.
European and international references applicable.
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.
Trusses and load-bearing beams for large roofs or sports facilities. The wood is planed and glued, remaining dry.
PRC.32 · Open the processDiamond-profile boards installed vertically for rapid water run-off. Often left to grey naturally.
PRC.02 · Open the processTraditional alpine roofing: small hand-split larch shingles following the natural grain for rain run-off.
PRC.41 · Open the processThe insulating core of the window frame is solid glulam spruce (warm), protected outside by an aluminium shell against rain.
PRC.27 · Open the processWeight for weight, Spruce has an excellent strength-to-mass ratio (close to steel). However, knots deviate the linear fibre flow, creating dangerous stress concentration points that dramatically lower the bending strength of the individual board.
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