Sustaining the sustainable

No other building material has the sustainability credentials of Europe’s softwoods. But, when used externally, care must be taken with design, specification and treatment in order to ensure an extended life.

Species

Larch is suitable, and an increasingly popular choice, for untreated external cladding. It is durable and weathers to an attractive silvery-grey colour.

Spruce (whitewood) has a denser structure than pine (redwood), making it more durable for external applications, although this strength also makes it difficult for preservatives to penetrate deep into the wood.

British Standards’ penetration requirements make allowances for the characteristics of different species. For example, the penetration requirements for cladding can be easily met using spruce.

Design

There are two simple rules to follow:

• avoid direct ground contact
• avoid standing water by ensuring adequate drainage from any wood surfaces

British Standards

For more information please see:

BS 8417 Preservation of timber

BSEN 351 Parts 1 & 2 Durability of wood and wood-based products – preservative treated wood

BSEN 460 Durability of wood and wood-based products – natural durability of solid wood – guide to the durability requirements for wood to be used in Hazard classes or visit  www.bsonline.bsi-global.com

Preservative treated

There is a wide range of preservatives available for all applications, up to Class 1 durability.

For greatest durability, use timber that has been pressure treated in an industrial process. The preservative manufacturers are continually developing products that are more environmentally-friendly, without compromising the extended life of the treated timber.

Examples include Arch Timber Protection’s Tanalith E and Osmose’s Naturewood, water-borne products using copper from recycled sources and organic biodegradable biocides.

For more details visit:
www.archtp.com and
www.osmose-europe.com

Where pressure treated timber is cut, notched or bored, care must be taken to treat the exposed area with a suitable end grain preservative. Anything that is planed or regularized should be sent back to the plant for re-treatment.

For more information on factory finished and brush applied coating systems visit www.sikkens.co.uk

Disposal of treated timber should be through incineration in energy-producing plants. Contact your local council for details of suitable sites.