A competent professional installer should be consulted in order to survey each particular site, assess the conditions, and take responsibility for the installation. We recommend that you provide them with a copy of this document and our telephone number. We are always happy to discuss the specifics of your project.  The desired service life of cladding is heavily reliant on good design, good installation, and best practice principles.

Every project is different! Woodtrend suggest referring to the Trada Publication External Timber Cladding ISBN 1900510308 and the TDCA (Timber Decking and Cladding Association) website http://www.tdca.org.uk/

There are many possible profiles and species that are suitable for cladding. Woodtrend stock hardwood cladding in Ipe, Garapa and Cumaru. We can also manufacture other profiles in different species. We discuss each project and work out what specie, in which profile and with what installation method is ‘fit for purpose’.

Choice of Timber

There is a wide choice of species available. Ipe cladding is normally used Air Dried and Cumaru, Garapa, Balau and Massaranduba recommended to be used Kiln Dried. We also supply Thermowood Pine and Siberian Larch.

Sizes sold are as at the time of manufacturing, the wider the board the more variance one has.  We do not recommend Air dried boards for cladding wider than 145mm. Many markets with a hot climate prefer narrower cladding boards 90mm to 110mm because the shrinkage on narrow cladding is less and this results in less variation of the gaps between the boards.

Ventilation

This is crucial. There must be a minimum of 20mm cavity to allow for adequate air circulation behind the timber. This prevents condensation on the underside of the cladding board which can result in cupping and warping of the boards.

Support Battens

Support battens should not exceed 600mm spacing whether vertical or horizontal. Limiting the spacing of the support battens will help prevent timber’s natural tendency to twist, bow and cup, 

Screws and fasteners

Stainless steel screws only to be used. Pre- drilling is necessary as these are dense timbers. Have sufficient drill bits available!

Insect Mesh

The cavity behind the timber cladding can provide a dry home for various types of insects. Install insect mesh at the openings at the top and bottom of close jointed vertical or horizontal boards to inhibit insect access and infestation. The mesh should be of a gauge to allow free flow of air and water. Insect mesh is available in stainless steel and fibreglass.

Spacing

Wood is a natural product which is affected by the environment. Air Dried cladding will shrink after manufacture and this results in slightly varying widths in the cladding boards.  The degree of shrinkage depends on the climate and site conditions. If the cladding is installed in the humid and wet season, then one should expect shrinkage in the dry season and allow for this accordingly. If the cladding is installed in the dry season, then the boards will have shrunk during the acclimatisation period prior to installation and one can expect the boards to swell again in the humid/wet season. It is advisable to allow a 2mm gap between the tongue and groove of our profile to allow for movement. Note: Kiln Dry cladding can also shrink but generally much less than Air Dried cladding. Kiln Dried boards can take on moisture and swell, so it is necessary to take this into account.

Moisture Movement

Many installers lay out the boards and let the cladding acclimatise on site for a week before installation – they will judge the expected shrinkage and/or contraction to be expected in the climatic conditions accordingly.
There is always movement due to weather changes and conditions after installation – this is natural and normal (see below on MC).

Appearance and grading

A competent professional installer will take good care in the design of the cladding and the selection and trimming of the cladding boards during installation. Always allow for about 10% extra when ordering your cladding to cater for this.

Slight hit and miss can easily be sanded out and sticker marks in air dried cladding will fade out after installation and these should not be trimmed out or rejected. Seasoning checks on the face of the board are to be anticipated and do not affect the stability or strength of the board. Any structural defect such as deep cracks, torn tongues, and any other damage from transporting or storing the timber on site, should be trimmed out.

Moisture Content

AD (Air-Dried) timber: Installing Air Dried timber is only appropriate for very stable timbers such as IPE.  Cumaru or Garapa should be installed KD (Kiln-Dried).
KD (Kiln Dried) timber: The key to stability in timbers such Cumaru and Garapa is even kiln drying to an average Moisture content of about 14 percent and good fixing on battens with centres no greater than 600mm.

Butt ends

Butt Joints are the key to a good cladding installation. Remember stainless steel screws only.

Boards must always be butt jointed over battens whether vertical or horizontal. Single battens are not always wide enough and double battens may need to be used. Plan this in advance.   
Select the timber carefully and match the widths for even butt joints for each row.

End trim for a clean square end and trim out visual/structural defects and always trim to the centre of the nearest joist.  Always seal after trimming.

Each board of cladding must have one stainless steel screw per batten intersection (screwed in at an angle, through the tongue and into the batten. Never join a board between the battens.
Hardwoods are hard to hold in place in exterior service and sometimes (during installation or later during snagging) one has to reinforce the difficult bowed cladding boards after wedging them straight with a top down fixing, countersunk stainless screw and plugged to conceal the screw.

Care should be taken to keep ferrous metal such as scaffolding and non stainless steel metals away from the cladding as this can cause unsightly marks and staining.

End Sealer

Cladding ends should be sealed after trimming on site to help prevent splitting and checking on the ends of boards. During installation, we recommend that boards are end-sealed immediately after cutting.  A clear, water resistant wax or penetrating exterior oil should be used.

Finishing Options

In order to inhibit surface checking and discoloration, cladding can be finished with an exterior oil, but many users prefer to leave the cladding to grey naturally. Left untreated, most hardwoods including Ipe will weather to a natural silver-grey colour. If you decide to finish the cladding it should be treated with a penetrating sealer (exterior oil) in dry conditions in accordance with the oil manufacturers instruction. It is important to understand that treating only one side of the cladding material creates an unequal moisture transfer and may result in some slight cupping. If cupping does occur is usually settles after the wood has seasoned and the moisture equalises again.

It should be noted that oils can only inhibit early bleaching/weathering – they cannot stop it.

Bleached weathered timber may also show small checking which also expand and contract according to the exterior weather conditions. This does not affect the strength of the timber.

Maintenance

Woodtrend untreated boards are designed to be left to bleach and little maintenance should be required. The speed of the weathering will depend on the degree of exposure to the sun and the weather. For more detail please call and discuss. We aim to avoid excessive cleaning and maintenance costs!

Please note that the above are our recommendations without liability and we repeat that a competent professional installer should be consulted in order to survey each particular site to correctly, check the cladding moisture content prior to installation, assess the conditions and take responsibility for the installation. Woodtrend shall not be held responsible for any consequences arising from any errors or omissions on this guide for any damages resulting from the use of this information.

Updated 6 July 2015.