External timber cladding and roofing battens are not interchangeable – they have different exposure risks and, potentially, different dimensions. The Timber Decking & Cladding Association explains what you need to know.
Timber cladding is installed as a rainscreen on buildings in the UK. The timber battens used on these projects should create a cavity that allows airflow and moisture to escape, ensuring the longest possible service life for the cladding.
Not all wind-driven rain is deflected by rain screen cladding; moisture gets into the cavity. Therefore, the timber used for battens must be sufficiently durable to perform well under these conditions. So, are you selling the correct battens for the job?
What is the right batten type for cladding?
Effective timber cladding battens have a service life similar to or better than cladding boards. Pressure-treated softwood, such as spruce or pine, is the go-to material for cladding battens, which has a typical service life specification of 30 years.
Battens should always be supplied with written evidence of treatment detailing the appropriate Use Class (timber components are assigned to different Use Classes according to the exposure risk) and desired service life. It’s helpful to mention this in the specification notes of any plans.
Why can’t roofing battens support exterior timber cladding?
Cladding battens are assigned to Use Class 3 and, if pressure-treated accordingly, are suitable for external use above ground.
Roofing battens, however, are assigned to the lower Use Class 2 as they rarely get wet and should not be used to support cladding.
Should cladding battens be fixed vertically or horizontally to the wall?
Only vertical battens are required for horizontal timber cladding. These battens should be 50mm wide x 38mm thick but can be 50mm x 25mm if there’s no side jointing.
Where cladding is used in a vertical arrangement with horizontal support battens, a vertical counter batten is necessary to create a drainage plain and allow the free passage of water. Counter battens should be at least 50mm wide and 25mm thick. These dimensions are to help ensure the battens will accept fixings without splitting.
When selling battens, it’s worth asking the customer how they plan to orientate their cladding to ensure they build a drainage cavity behind their cladding.
Is it necessary to slope the top of external cladding battens?
It’s a long-held theory that sloping the top of cladding battens will help with longevity, as the slope will aid water shedding. Fitting the battens so the slope directs water into the cavity makes logical sense, but no hard evidence supports the theory. Sloped-top battens are preferential in a belt-and-braces approach to quality.
Must cladding battens be strength-graded?
Engineers use strength classes to conveniently define timber’s minimum strength, stiffness, and density characteristics.
However, the engineer only needs a characteristic density (defined as the mean density) for the wood species for fastener calculations involving cladding battens. The other characteristic values defined by strength classes (lower 5th percentile values for strength, stiffness, etc.) can be ignored.
Consequently, strength-graded timber isn’t used for cladding battens. Instead, the battens are either sorted on-site to exclude large defects (big knots, splits, rot, etc.) or bought already graded in accordance with BS 5534 (the roofing batten standard). BS 5534 isn’t a strength-grading standard as such.
The wood species used for cladding battens are UK-grown larch, pine, and spruce or their imported equivalents, as defined in BS 5534. These species all have a minimum mean wood density of 350kg/m3 (at 12% moisture content), which gives adequate connection strength for cladding fasteners.
Provided the wood species used for cladding battens are specified in accordance with BS 5534 (code of practice for slating and tiling for pitched roofs and vertical cladding), it will meet the engineer’s minimum density requirements.
Help TDCA make every timber cladding project a successful one
At the Timber Decking and Cladding Association (TDCA), our mission is to raise awareness and demand for quality timber decks, associated landscape structures, and external timber cladding, which goes hand in hand with the best-practice workmanship required to produce such projects. With your help, we can get closer to stamping out poor workmanship altogether.
As a totally independent but industry-respected body, we offer expert advice and objective, unbiased opinions, which are vital for people experiencing issues with the quality of the materials or workmanship used on their timber decking or cladding projects. It’s fair to say we’ve seen more than our share of poor practices, creating problems that could have been easily avoided.
You can find practical information in The Timber Cladding Handbook, freely available online. We also offer an advisory service for unanswered queries – use the Contact Us form on our website to submit any questions.
For more detail, refer to BS 8605 External Timber Cladding Part 1 – Method of specifying, designed to help manufacturers and specifiers. TDCA offers a 15% discount to purchasers.
Find all this information and more at www.tdca.org.uk
* This article was originally published in the November/December 2024 issue of TDUK’s Supplying Timber magazine.
