Get your cladding quality right

John Russell of Russwood explains why using a premium quality timber cladding, along with the right fixing system, is vital to ensure your cladding looks good for the long term

The popularity of timber as a cladding material is on the rise, with many self-builders choosing to specify it for their project. The environmental and sustainable credentials of timber are proving to be of increasing importance to those who want to minimise the impact of their build on the environment. As a recyclable, renewable resource with low embodied energy and important carbon capture and storage properties, timber is the obvious choice for the environmentally conscious self-builder.

Aesthetically, timber adds warmth and texture to a building and when correctly detailed and fixed, timber is highly durable and easily maintained. If you want your timber cladding to look better and last longer, it’s important to consider not only the quality of timber used but the way in which it’s fixed. Low quality timber which has been poorly fixed can cause problems down the line which can be costly and inconvenient to resolve.

To avoid such problems, ensure that the timber you select is of premium quality. Siberian larch is a good option for most projects – it’s one of the most naturally durable species, and the presence of tannins in the wood create a high resistance to decay and rot, making it one of the toughest and most durable softwoods. Its high density means that it’s more difficult for decaying organisms to penetrate the wood.

Siberian larch is extremely versatile, being suitable for most external timber cladding applications. Durability can be combined with a clean, relatively knot free look (for example in Russwood’s SILA A/B grade timber), which is ideal for design-led projects. An A+ grade option provides a clean, consistent, almost knot-free look, combined with excellent durability. By contrast, SILA B/C is a more rustic grade, giving a knottier, less uniform look, without compromising the material’s durability properties.

A reputable manufacturer should source all its timber species, including Siberian larch, from sustainable forests. They are then generally imported to the UK in board form and, depending on which mill it came from, will have a variety of surface finishes, such as circular sawn marks, twin arbour lines, paint marks, grease marks or compression marks from steel securing bands. To avoid an unsightly surface finish, skimming the face of each board provides a clean, unblemished and fine-sawn finish.

For an optimal moisture content for external cladding, timber needs to be kiln-dried correctly – for example SILA is kiln-dried to approximately 16-18 per cent (plus or minus two per cent). This moisture level is retained until delivery to site and your cladding can then be installed immediately upon delivery.

Cladding arrangement makes a big impact on the aesthetic of your project. We’re seeing trends for mixed width boards as well as mixing up horizontal and vertical cladding. Enhanced performance of dimensional stability can be achieved by using narrower widths, for example 120 mm, and 95 mm.

If even weathering is a concern, an open rainscreen profile maximises the chance of consistency – for example a rhomboid shaped profile means air is able to circulate around the whole cladding board, allowing the timber to fully dry out between wetting cycles.

A common pitfall for self-builders is the use of incorrect fixings. While it may seem tempting to try to save on costs here, durable timbers such as Siberian larch are often quite acidic so high-quality stainless-steel fixings should be used. This will avoid corrosion and staining and the appearance of stainless steel will remain constant, whereas galvanised and copper nails will change colour over time.

Appropriate fixings will further enhance the durability of your cladding. For example SIHGA’s FassadenClip, fixed using precision engineered stainless steel screws, is designed to be an ideal fixing system for rainscreen cladding. This type of ‘secret fix’ system creates a free flow of air between the back face of the cladding board and the vertical batten, enhancing ventilation and thereby increasing the durability of the timber. The secret fix element means the front face of the facade boards are left fully intact for a clean and contemporary look. We recommend leaving an 8 mm open shadow gap between boards and using a black, unbranded, UV-resistant breather membrane to avoid the membrane showing through the gaps. This type of fixing system also provides the flexibility of allowing the cladding to be easily removed at the building’s end of life or repositioned, for example if you choose to extend.

For a neat way to deal with visible fixings, consider using a stainless steel screw such as SIHGA L-GoFix A2 – precision milled from hardened, A2 grade stainless steel. The sharp flanks of these screw threads are designed to allow the best possible anchoring without causing the timber to split. They are also self-drilling so there’s no need to pre-drill (unless you’re using a dense hardwood).

A compensation strip can be used to aid ventilation, as it creates a gap between the timber elements of the facade, and can be applied to both vertical and horizontal cladding. For horizontal cladding, it is simply fixed to the vertical batten whilst for vertical it should be fixed on the upper edge of the horizontal batten to ensure that a water trap is not created.

Cost is inevitably a factor for self-builders, and can vary hugely between timber species and grades. Premium quality timber cladding is inherently durable, meaning no protective coating will be necessary if detailed and installed correctly so the decision to coat would purely be an aesthetic one. It might seem tempting to select a cheaper timber but bear in mind that cheaper, less durable timbers will require treatment and regular maintenance, which may prove more costly in the long run.

John Russell is managing director at Russwood