Cladding a timber frame home
Keen to achieve a high-quality finish on your timber build? Here’s what you need to consider when specifying and installing different facade options
Learn about the different methods of exterior coverings you can use with this popular structural system
Offering a quick and cost-effective route to an efficient, high quality home, it’s easy to see why timber frame is a popular system with self builders and home extenders. If you’re wondering which claddings will work best for your timber build, here’s the short answer: they can all work. But that’s not the whole story. Some finishes complement a timber construction better than others, for instance – but should that be the be-all-and-end-all of your decision?
Timber frame basics
Before we get into the nitty gritty of selecting your preferred cladding, let’s refresh the memory about what goes into a timber frame project and the key benefits of using this kind of structural system. Fundamentally, a timber frame home is constructed using large panels, which are usually pre-insulated in the factory. Most of the design and construction is computercontrolled, so you get accuracy and quality as standard – and there is less labour requirement on site compared to using, say, masonry. That leads us to one of the big attractions of this method: once work starts on site, you can expect the weathertight shell of your home to be up in as little as five to 10 days, ready for your trades to kit out inside and out. So whilst the plumber is ferreting away on getting the pipework network in place, the external roof and wall finishes can be applied at the same time. Using a factory-manufactured structural system also means you can achieve good energy performance within a relatively thin wall profile. According to Kingspan Timber Solutions, to get to a U-value of 0.17 W/M2K (a fairly typical level to aim at on a self build), you’d need a wall profile of 435mm with standard masonry. Using a highperformance timber frame, you can achieve the same standard with a total wall thickness of just 312mm. That could mean more floor space inside the finished property.
What are the design options?
Any architect or designer worth their salt will be familiar with conventional framing, while many timber frame companies have in-house designers who will help you plan your dream bespoke home. This can help to remove the hassle and make for an efficient, plain-sailing and cost-certain design and build process.
Timber frame projects come in all shapes and sizes. Your designer should be able to tailor your house to your unique budget, taste and plot demands. You can even mix timber
frame systems with other materials such as steel frame and oak to cost-effectively create desirable features like characterful glazed gables, wide spans of sliding doors and big open-plan layouts. What’s more, you can finish the frame externally in whatever cladding system suits your style, brief and budget. “These days, three out of every four timber frame builds we work on is clad in a lightweight system,” says Simon Orrells from Frame Technologies.
Timber weatherboarding is a classic choice, but you can also consider products such as fibre-cement, render boards and brick slips (slithers of masonry cut from the block or extruded as tiles). All of these options are quick to install and require minimal wall build-up.
“Pre-finished claddings are becoming more popular,” says Simon. “Fibre-cement offers improved fire protection compared to timber, for instance – but it’s not any more expensive once you’ve accounted for the upfront cost, sundries and treatment required for wood boards.”
How are lightweight claddings fixed?
The basic premise is similar across pretty much all the options – from render to fibre-cement boards. From inside to out, the walling profile goes: timber frame panel; vapour barrier (which is sometimes known as a breathable membrane); battens; backing board (if applicable); and final finish (eg wood cladding).
The battens – typically wood, though some systems use metal brackets – are vital for creating a cavity. This ensures that there’s sufficient airflow between the external finish and the main structural frame. So any moisture that penetrates is evaporated away before it can damage the building fabric. According to the Timber Decking & Cladding Association, for wood cladding, a standard ventilation gap would be at least 21mm – but the exact specification will depend on the product you’ve picked and the manufacturer’s instructions for installation.
Cedral recommends a minimum 30mm airgap for its fibre-cement boards, but suggests using 38mm-deep battens. Products such as Euroform’s Rendaboard are usually installed with a 50mm cavity.
One thing that can differ slightly is how you purchase the cladding. “With options such as fibre-cement, you’re
buying a complete system from a single supplier, including the pre-formed flashings, trims, fixings etc,” says Simon. When it comes to brick slip systems, some are glued to a backing board, while others simply clip into a track.
Is it possible to mix and match?
Another advantage of using lightweight products on a timber frame is that it’s easy to combine different elevation finishes. Counter-battened render board, for instance, will sit comfortably alongside fibre-cement – giving you an interesting aesthetic using low-maintenance materials.
Simon highlights brick slips as a great option for this kind of application. “It’s not usually cost-effective for a whole house, but it’s exactly the same colour and material as masonry and can give you more design flexibility,” he says. Consider using it above wide spans of glazing to cut down on lintels, or for features such as cantilevers, where its lightweight nature will help to reduce the need to use additional steelwork compared to using standard masonry.
“One thing you need to be careful of with timber frame is changing the cladding after the technical design phase,”
says Simon. “We devise the structural shell with the cladding in mind to accommodate wind loads – so if you wanted to switch from, say, a brickwork external wall to a lightweight timber finish, you’d need to get the design rechecked to ensure it will deliver the required results.”
The same holds true in terms of energy performance. As a masonry external finish will have a standard cavity of 50mm, there’s more airgap than with lightweight claddings; and a bigger cavity will give you slightly better insulation. That can be easily addressed before the panels go into production – but it’s not so straightforward later on.
Can I use brick or stone?
While lightweight cladding solutions can complement the benefits of timber frame, they’re certainly not your only option. Perhaps you would prefer the look of a masonry finish, or you think that the use of a full brick or stone product will fit in better with the setting and architectural form of the surrounding houses.
Special wall ties are available to secure masonry cladding to the main superstructure while allowing for differential movement between the two materials. These are usually nailed into the frame, and bedded into the mortar layer.
In most parts of the
UK, you will need 4.4 ties per m2, increasing to 7 per m2 in severe wind load locations – but the exact spec will be determined at the structural design stage. The standard cavity depth for brickwork on a timber frame structure is 50mm, and many ancillaries – such as lintels – are designed to suit this.
“You can go as low as 38mm in some cases, though,” says Simon.
If you’re keen to go for a stone finish, bear in mind that traditional random stone walling is extremely uneven. It’s therefore typically built up against a backing block to protect the cavity – adding to the wall thickness and increasing the amount of wet-trade work that goes into the project. “It does give you very wide walls,” says Simon, “but you could just use stone on the front elevation and switch to render elsewhere.” Alternatively, pre-cut products are available that can be laid much like conventional brickwork.