The principal considerations when choosing timber cladding are:
Price can vary significantly from material to material. Naturally durable species from which all sapwood is excluded tend to cost more than less durable softwoods protected with wood preservative by an industrial process. Cost relates to the availability of a species, the quality of material, performance and level of processing involved.
Desired service life
The prediction of service life is not precise because a range of factors can affect it but generally length of service will relate to the durability of the timber against fungal and insect attack. For extended service life (30 to 60 years) always choose an appropriate naturally durable, preservative treated or modified wood species.
Durability against decay and insects
Cladding is a BS EN 335-1 Use Class 3 application. Where sapwood is not excluded, appropriately durable timber should be specified.
Fire retardant treatment
If required by building standards, always check to ensure that the cladding species, profile size and cavity design reflects accurately the Fire Certificates of the treatment under consideration.
Careful detailing to prevent moisture retention and to minimise the effects of moisture movement (expansion and contraction) are essential in all designs. Materials with enhanced durability provide an insurance against detailing failures and poor installation practice/maintenance.
Is a natural or coated finish required
If a natural look is required then only naturally durable or species treated with an appropriate preservative or modified wood should be specified. Surface coatings do afford a degree of protection to untreated low durability softwoods but for best results they work best on cladding materials that are more dimensionally stable like modified woods or on preservative treated wood.
What maintenance regime is acceptable
If maintenance, repair and replacement is likely to be difficult and costly then the highest durability of cladding permitted by the budget should be chosen. All coated cladding will require recoating at some point.
Resistance to impact damage and vandalism
Species with a low density (physical hardness) are more susceptible to impact and surface damage and should never be used at low levels where there is the potential for abrasion, scraping or vandalism.
Source certification schemes from managed forest resources are now well established for both home grown and imported species. Look for materials from FSC and PEFC accredited sources for absolute reassurance.
For any given species, appearance, strength and durability are determined by the quality selected. Knot size, knot frequency, grain orientation, type of machining and whether sapwood is included or excluded all have a bearing on quality. Where naturally durable, preservative treated or modified woods are specified, the TDCA recommends that the cladding is processed using a Factory Production Control system (FPC), with third party accreditation such as ISO9001.
Supplier support services
Make sure that the supplier you select has the ability to provide the range of support services required prior to, during and after installation. Samples supply, supply volume and quality consistency, technical expertise on the chosen material, handling advice and snagging and quality dispute resolution policies are all critical service factors to be considered. Look for suppliers with the TDCA CladMark quality accreditation which means their capabilities and policies have been independently assessed.