Understanding Timber Cladding

There are multiple, even infinite possibilities when it comes to timber cladding. It provides a natural, warm appearance while offering protection to the building envelope. Historically, timber has been a staple in UK architecture, from traditional cottages to modern, eco-friendly designs. 

Timber cladding is considered for its sustainability, versatility, and ability to blend well with various architectural styles. It can give a beautiful appearance to a building both internally and externally. Here we will look at timber cladding details on the external walls of a building.

Types of Timber

Softwood timber such as cedar, larch or pine are common choices. Cedar is valued for its resistance to decay and insects, while larch offers good durability and a distinctive appearance. 

Hardwood timber such as oak, iroko and teak are more durable than the softwood alternatives with rich and varied aesthetics, but often are more expensive. 

The timber chosen for cladding must be durable and fit for purpose. British Standards have a class system for the durability of wood ranging from Class 1 – Very Durable to Class 5 – Not Durable. 

This classification is set out in BS EN 350:2016 and applies to the heartwood only. Sapwood is not considered durable in any species and should be excluded from cladding boards unless preservative treated. For timber cladding Class 3 or better can be used without preservative treatment. But this depends on exposure and detailing, so it is worth checking manufacturer guidance on anything facing a very exposed elevation. 

Timbers can suffer from movement and dimensional changes which will vary by atmosphere, board thickness, species and so on.

Softwoods tend to be the most popular choice for timber cladding with a good variety available. Species such as European Larch, European redwood, Douglas Fir, Western Red Cedar are all options. Many of these are grown in the UK and are a good sustainable choice. 

It is worth noting that European redwood (Scots pine) falls into durability Class 3-4 and will generally need preservative treatment for untreated exterior use, unlike Larch, Cedar and Douglas Fir, which can usually be specified untreated at Class 3. 

There are a variety of treatments, preservatives and surface protections available which go beyond the scope of this blog post. Timber Development UK (TDUK) (formed from the 2021 merger of TRADA and the Timber Trade Federation) as well as the Timber Decking and Cladding Association (TDCA), which publishes cladding-specific guidance including the Timber Cladding Handbook, are both great places to investigate this further.

Timber Cladding Profiles and Styles

Horizontal timber cladding is probably the most common, and perhaps simpler option. The boards are nailed to vertical battens on the substrate – this could be masonry, timber frame etc.

Vertical timber cladding can come in the form of tongue and groove, or board on board, along with open joint options too. Generally vertical timber cladding will require counter battens to enable moisture run off in the cavity.  The most popular is board on board which is tolerant of timber movement. 

Diagonal timber cladding angles the boards at 45 degrees and fixes them to vertical battens, or sometimes even diagonal battens which still allows for the run off of any moisture in the cavity. 

Shingles are timber tapered ‘tiles’ which are fixed overlapping one another to give a similar appearance to roof tiles. They are quite a traditional form of timber cladding and particularly popular in North America, however they are also seen in many contemporary applications. 

There are many different types of profiles that can be used for timber cladding including:

• Feather edge – triangular in section these boards are installed with a small overlap. The shape helps shed water off each board. Used in horizontal installation
• Open gap – boards with a small gap in between, with an angled profile. Used in horizontal installation.
• Shiplap – boards are similar to open gaps but they have an overlapping joint to keep water out of the ventilated cavity. They can be used in both horizontal and vertical cladding.
• Tongue and groove – boards are similar to shiplap but create a stronger joint between the boards. These can be used vertically and horizontally.
• Board on board – vertical boards placed alternating with one beneath and one on top creating shadow gaps. This type of cladding is not recommended in horizontal cladding.

Finishes and Treatments

Applying finishes and treatments to the timber can enhance durability and appearance of the timber cladding.

Natural finishes such as oils and stains penetrate the wood, providing protection against moisture and UV rays while enhancing the natural beauty of the wood.

Paints can provide a protective layer and good colour options but must be breathable to prevent moisture trapping. 

Preservatives can prevent rot, decay and insect damage, especially in less durable wood species. The reapplication of these treatments should form part of a regular maintenance programme.

Key Components of Timber Cladding Detailing

Moisture is the biggest enemy of a timber cladding detail, so the design of timber cladding must ensure that suitable steps are taken to avoid moisture penetration or damage. 

Timber cladding is designed as a rainscreen principle – which means that the cladding will have some moisture penetration and it is the system behind the cladding – the waterproof membrane, that will ultimately protect the structure from moisture. This secondary weather protection consists of the waterproof membrane, flashings and DPCs along with the vented cavity that allows any excess moisture to drain out of the cavity to the outside. The battens and counter battens provide the ventilation and clear drainage for the cavity.  An insect mesh is fitted to the top and base of the cavity to ensure the cavity remains clear.

If there is masonry behind the cavity, a waterproof membrane is often not necessary. Although, this depends on the site’s exposure category and whether external insulation forms part of the wall build-up. In more exposed locations or where the insulation sits within the cavity, a breather membrane meeting BS EN 13859-2 is still generally recommended. Make sure you confirm this with the membrane manufacturer. 

The cavity itself should be a minimum of 25mm wide, increasing to 38mm or more on highly exposed sites or where open-jointed cladding is specified, since a wider cavity improves the drying potential behind the boards. 

The timber cladding is also susceptible to water damage from splash zones – ie at the base of the building, so the cladding must be lifted by a minimum of 200 to 250mm. 

Battens are usually placed between 400mm and 600mm centres. For diagonal boards the battens are brought closer.  Horizontal cladding boards are fixed to vertical battens which allow free draining down the cavity and air circulation. Vertical boards are fixed to horizontal battens which in turn are fixed to vertical battens to allow for free drainage and air circulation. The battens should be sized to suit the board profile and site wind loading with common sizes being 45x45mm or 50x38mm treated softwood. It is worth checking manufacturer or TDCA guidance.

Fixings also need careful specification, as the wrong choice can cause staining or premature failure. Stainless steel fixings are recommended throughout. Grade A2 (304) is generally adequate, but marine-grade A4 (316) should be used within a few kilometres of the coast or in other corrosive environments. Fixings are usually positioned at quarter points across the board width, at least 20mm in from the board ends, to reduce the risk of splitting. 

Regulatory Considerations for Timber Cladding

It is important to always ensure compliance with building regulations in the design and installation of timber cladding. Key regulatory considerations include:

Planning Permission

Obtaining planning permission may be necessary, particularly for listed buildings or those in conservation areas. Understanding local planning policies and engaging with planning authorities early can streamline the approval process. 

Often the cladding must complement the surrounding architecture and landscape. Materials, colours, and profiles should be chosen to enhance the building’s aesthetic while respecting local character.

Demonstrating the sustainability benefits of timber cladding, such as reduced carbon footprint and enhanced biodiversity, can support planning applications.

Building Regulations

The Building Regulations prescribe requirements for structural integrity, fire safety, thermal insulation, in relation to timber cladding design and construction. It is important to ensure that timber cladding meets these standards to obtain regulatory approvals and certifications.

Adhering to Approved Document Part B (Fire Safety) involves using fire-retardant treatments and ensuring proper firebreaks. The Building Regulations include information for using combustible materials for cladding and these must be followed. There are different classes for products that control the surface spread of flame, and treatments accordingly.

The most significant recent change affecting timber cladding is the ban on combustible materials in and on the external walls of relevant residential buildings. Introduced in December 2018 for buildings with a storey at 18m or more, this was extended from 1 June 2022 to residential buildings including flats, care homes and student accommodation with a storey at 11m or more. 

Above this threshold, cladding materials must achieve European Classification A1 or A2-s1,d0 to meet BS EN 13501-1, which rules out untreated timber cladding without a fire-engineered alternative. Below 11m, most houses and low-rise buildings can still use timber cladding, though the boundary-distance rules of Approved Document Part B still apply, since combustible cladding counts as an unprotected area of the wall. 

Fire-retardant treated timber achieving a Euroclass B-s1,d0 rating is available as an alternative for projects close to the height threshold. Part B‘s external wall guidance also remains under active review by the Building Safety Regulator following the Grenfell Tower Inquiry. Check the current edition before finalising a specification on any project with a storey above 11m. 

Cavity barriers are required behind the cladding in locations such as around window openings, or compartment floors, to restrict the movement of smoke and flames behind the cavity. Again, it is worth checking the Buildings Regulations for exact requirements.

Approved Document Part L (Conservation of Fuel and Power)  doesn’t apply to the cladding itself but does affect how the system is detailed. Battens fixed through insulation to the substrate can create thermal bridges, therefore specifying low thermal conductivity battens or a batten arrangement that limits penetrations through the insulation layer, helps the wall build-up meet current Part L targets. 

Approved Document Part A (Structure) covers structural integrity, ensuring the building can support the cladding system. 

Environmental Impact

Sourcing timber from sustainably managed forests is important. Certifications like FSC (Forest Stewardship Council) and PEFC (Programme for the Endorsement of Forest Certification) ensure responsible forestry practices. Additionally, adhering to sustainability standards such as BREEAM can enhance the environmental performance of a project:

Timber also sequesters carbon during growth and continues to store it for the life of the building. This is increasingly recognised in embodied carbon assessments and can strengthen the sustainability case in a planning application. 

Ensure that the timber used is sourced from responsibly managed forests that promote biodiversity and prevent deforestation. Also consider other factors such as transport, manufacture and maintenance when selecting the timber cladding species.

More Timber Cladding Detail Examples

If you’re looking for fully resolved timber cladding details to use directly in your projects, our sister site Detail Library has an extensive range covering horizontal and vertical cladding types, board on board, cladding to brick transitions, and foundation junctions available to download in CAD, Revit, and SketchUp.

The Detail Library is built for architects, technologists, and designers who want a reliable starting point for technical design — so you’re not building every detail from scratch. Details are fully resolved, not just component libraries, and they’re updated regularly as standards and regulations change.

Timber Cladding to Brick Transition Detail (DL75)

Board on Board Timber Cladding (DL85)

Timber Cladding to Foundation Junction Detail (DL174)

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