British Larch Sawn External Cladding

Length:

Random lengths: 1.8-4.0 m. Lengths of over 4.0 m may be included but are not guaranteed.

Orientation:

Horizontal or vertical.

Appearance:

British larch ranges in colour from pink-brown in the heartwood to creamy-white in the sap band. There are frequent dark brown knots, which can loosen as the wood dries. Some boards may contain open resin pockets that may ooze during the first year and during subsequent hot summers. When exposed to the elements, the wood will, over time, weather to a silver-grey colour.

Technical properties:

• Moisture content: Wet.

• Natural durability (to BS EN 350-2): Moderately durable, Class 3–4.

• Insect attack: Resistant.

• Service life (to BS 8417): Occasionally wet: 15–30 years (in practice untreated larch cladding lasts nearer 30 years); frequently wet: <15 years.

• Treatability class: Resistant.

• Movement class: Large.

• Resistance to impact: High.

• Resistance to fixing: Medium.

• Mean density (when dry): 470–650 kg/m³.

• When to fix: Winter monthly only.

• Grading: Too knotty to be graded under any standard.

• Working properties: Good workability, takes fixings satisfactorily.

• Extractives: Contains resin rather than oil or tannin. The resin does not tend to bleed and is not reactive.

• Emission of formaldehyde (to BS EN 14915): E1 (not significant).

• Reaction to fire (to BS EN 14915): Euroclass F (untested), D-s2, d0.

• Fire treatment: Not possible by impregnation.

Width:

- Waney-edge:

Random width: 200-350 mm. Widths of over 350 mm may be included but are not guaranteed.

Fixing:

Face fixed with stainless steel nails.