Learn more about... timber cladding

Timber cladding is popular with building owners and architects seeking to maximise timber’s unique visual appeal and environmental credentials. It is used for internal or external applications, although you must consider the durability of the timber when selecting material for external use.

Timber cladding has long been used to construct the external walls of buildings, either as the primary form of structure and enclosure or merely to enclose a separate structural frame. As construction in the UK now embraces the concepts of sustainable development, ‘dry’ construction (construction without the application of plaster or mortar) and increased prefabrication, and because of the variety of profiles possible with timber cladding, its popularity is likely to rise even further.

What type of fasteners should I use with timber cladding?

Stainless steel or non-ferrous fasteners are preferred to prevent long-term corrosion and possible chemical reaction with some timber species.

Softwoods can generally be fixed with suitably sized ring-shank nails, but it is recommended that hardwoods are fixed with screws and washers through oversized holes where double fixings are used. There are options for discreet fixing, but this is an area where specific advice should be sought from an expert source.

I want to clad onto a curved surface. What should I consider?

Horizontal boards cannot be easily bent around tight radial curves, particularly if they have a tongued and grooved profile. It is therefore preferable to use vertical boards, with horizontal battens that curve. This curvature can be achieved, for example, by building the battens up in layers thin enough to be bent cold, before fixing them into position by gluing and screwing.

Does timber cladding need fire retardant treatment?

There are Building Regulations in place which are intended to restrict the spread of fire. Depending on its location, wood cladding may require pre-treatment with a fire retardant, which must be compatible with any preservative treatments and coatings. Timber cladding may not be acceptable close to boundaries or above a certain height. It is recommended that you check with the Local Authority Building Control.

How can I remove staining that has developed on timber cladding?

Some woods have high extractives content, and this may take several months for the rain to ‘wash out'. Other staining may be due to excessive wetting, chemical staining, or pollution. There are a number of ways of removing stains, from washing to the application of chemical cleaners. The method of cleaning depends on the cause of the staining, and this can be identified by on-site inspection/investigation.

What board sizes are recommended?

There are many different profiles, but it is recommended that boards should be 150mm maximum width, to limit the effects of any moisture movement across the board. Tongued and grooved boards should be further limited, preferably to 100mm (max 125mm), with only kiln-dried wood used.

Board thickness is dependent upon the profile. It is also recommended that any individual part of the board, e.g., the tongue or top edge of a featheredge board, should not be less than 9mm in thickness.

What species are suitable for use in timber cladding?

Softwood is the most common choice for cladding in the UK, with home-grown species increasingly selected. A variety of hardwoods and modified woods are also suitable however.

When selecting species, consider the natural durability of the wood and the options for preservation and coating. Durable species may be more expensive to specify at the outset but may require less maintenance than a cheaper, less durable species.

Appearance (usually in respect of the size and frequency of knots) is also an important consideration and will determine which species to choose.

Where can I get more help?

BM TRADA timber experts offer independent timber cladding inspection, as part of their wider inspection, survey, and timber consultancy services. They are specialists in best practice principles, fault finding and diagnostic work on timber cladding boards, and carry out in-situ cladding inspections on a variety of installations for clients throughout the UK and abroad.

Free Timber Technical Helpline

Call our Timber Technical Helpline on 01494 840 349 during normal UK working hours (9–5, Monday to Friday).

The BM TRADA Bookshop

At BM TRADA, we have an extensive library of impartial timber information that has been carefully developed and maintained over decades. This collection includes the publication External timber cladding 3rd edition, an illustrated book containing in-depth guidance on the subject, along with the Wood Information Sheets Cladding for timber frame buildings, Timber cladding for building refurbishment, Finishes for external timber, and Specifying timber exposed to weathering. These publications are currently available in the BM TRADA Bookshop.

Visit the BM TRADA Bookshop

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