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British Larch Specification Sheet British Larch is used increasingly for cladding. Timber from the region is faster grown and contains a greater number of knots than the Siberian equivalent. It also shows a richer, warm colour and more vibrant grain. The key to delivering a quality product and making the absolute best of the British Larch resource comes down to investing the time in each of the appropriate production steps.

BSW Larch cladding production involves: • Sourcing FSC logs • Setting cutting patterns to saw cladding boards from the heartwood rich inner log. • Kiln drying to 18% +/- 2% • Visual grading based on European Standards before machining • Achieving high quality machined or sticker mark free sawn board surfaces • Regrading, based on European Standards after machining.

BS1186-3:1990. Notes from Timber for and Workmanship in Joinery. Part 3 Specification for Wood Trim and it’s fixing (some relevant sections). NB: Detail and confirmation should be taken from full standard.


Relevant Detail


Various stages at which timber cladding can be assessed and graded.


Moisture content of 13 to 19%.

Other than when timber is supplied in random lengths, timber should not contain knot holes and loose knots on exposed surface. Random length timber should contain no more than 1 knot hole or loose knot every 3 metres, on average.

Knots on an exposed surface which appear to be unsound or dead, but are not loose shall be permitted.

No limit is placed on splay, branch or margin knots where the surface cuts along the knot rather than through the cross section.


Other than end splits, no class of timber contain splits on the surface in the completed work. End splits on timber, before it is fixed in place shall be no more than 70mm.


No ring shakes permitted.


Resin pockets permitted.


No wane except where edge will be concealed on fixing.


Pith is permitted on exposed face.


All timber to be free of decay and insect attack.

BSW Larch grading of Kiln Dried Centre Core is based on BS1186-3, Type 3 and referred to as BSW BS1186-3 Type 3/4 Grade • All sound knots are accepted within grade. • Knots remaining in place through moulding are accepted. • Less than 5% of boards many contain knot holes. • No Selection is made for rate of growth or slope of grain. • Final grading should take place at installation.


3.1 Moisture content of 13 to 19%. 4.3.2 No ring shakes permitted. Section Relevant Detail 4.9 Pith is permitted on exposed face. 4.6 No wan...