Which Timber is Best?
Western redcedar is among the most popular softwoods used today. Aside from its relatively knot-free, ‘clean’ appearance, this softwood has a natural resistance to decay and moisture absorption, meaning it can typically be installed without treatment. It’s also the most stable of the softwoods, subject to little movement when installed.
If you did hope to apply a finish, its low resin content means it can be readily stained or painted. Added to this is the fact it can be worked to create a variety of profiles. But one downside is that it has a comparatively low density, which means it can be dented if knocked. It is imported from Canada and sometimes America, but increasingly grown here too (check the durability of the latter which can be a little lower than that of imported).
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The same is true of Douglas fir, which is another good softwood, also grown locally and sourced from Canada and the USA. UK grown Douglas fir may require a protective coating to improve durability.
Scottish and Scandinavian larch is denser than western redcedar, making it more resilient to knocks. It’s available in varying grades — the higher (quality) grades tend to contain fewer knots, being suitable for machined profiling, with lower grade sawn larch a cheaper option. Larch can however lose resin once installed, making it unsuitable with some finishes, and often requires pre-drilling before installation too; so check this with your supplier.
The temperate hardwoods, oak and sweet chestnut, are particularly hardy species. “Green oak will naturally weather with age to a silver-grey colour, and it has the advantage that no further maintenance will usually be required for anywhere between 25 to 100 years; this can be significant where cladding inaccessible areas such as the gable over a lower roof,” says Bill Keir of Oakwrights. “If, however, you want to keep it that initial golden colour, it will need regular and frequent treatment.”
Both oak and sweet chestnut contain high tannin levels (compared with some of the softwood options) which can leach out during exposure to the elements, resulting in dark streaks. Such marks do however disappear after a couple of years of weathering. Hardwood boards also need to be pre-drilled before being installed, which can add to installation costs. Tropical hardwoods such as iroko are also incredibly durable, but do ensure that the products you choose are from a sustainable source.
It sounds obvious, but look out for guarantees, with 15 years being minimum. One way to help ensure quality is to opt for products endorsed under a scheme such as the TDCA-operated CladMark.
In addition to these choices are an emerging group of thermally modified timbers such as ThermoWood, Accoya, Thor, Kebony, Keywood and PlatoWood. The latter are created by slightly different (patented) means, but the process typically involves heating lesser durable softwoods such as pine at high temperatures in order to remove moisture and resin and permanently enhance them. The timber may also be injected with chemicals. The result is a very durable and stable product. Many manufacturers also promote the sustainable benefits, with thermally modified softwoods offering a good alternative to depleting tropical hardwoods.
Do check with the supplier whether the product will require treatment with installation.
Low-Maintenance Timber Cladding
Tom Barnes, managing director of Vastern Timber, offers his advice on low-maintenance options
Cedar and thermally modified timber are less likely to move and allow you to use a more delicate joint. All wood will weather and go silver over time unless it is treated, but treatment adds to the upkeep of your cladding.
Osmo provides a UV protection oil which will slow down the weathering process, but their clear version is less resistant to UV. The pigmented versions perform better, but change the colour of your wood.
Sioo offers a product which accelerates the weathering process to turn the timber a pale silver. This means that you can ‘even out’ the silvering on different elevations, as they would otherwise naturally weather at different rates.
What are the benefits of thermally modified timber cladding?
Wood is made up of three things — cellulose, hemicellulose and lignin. When timber is heated at 210°C it reconfigures the structure of the wood and creates a mesh that prevents water entering. The hemicellulose is the part of the wood that bonds with water, and this decreases during the heating process so that the timber can’t bond with water.
As a result, the wood takes on the following properties:
- It becomes hygrophobic — it resists water and won’t take on any more.
- Is less likely to shrink or expand.
- Has increased stability and durability.
Getting the Details Right
It is crucial to get the corner details and those around windows and doors right when it comes to timber cladding, both for aesthetic purposes and to ensure moisture is not allowed to seep behind the boards. The most common way to deal with corners is to fix a length of timber which has been cut into at the back to form a V-shape that fits over the corner. The boards then fix into this piece of timber where they meet the corner. At windows and doors a vertical reveal should be used, protruding out slightly from the weatherboarding, which butts up to it. At all of these details, a mastic seal should be used to prevent moisture getting in.
Shakes and shingles are made from split logs and have an appearance more like timber tiles than boards. Although similar, shingles were originally sawn from a block, whilst shakes were split off using a chisel and mallet. Shingles tend to look neater and more precise than shakes, which give a more rustic appearance. As a cladding material they look fantastic on both contemporary and traditional homes. Shakes are usually made from Western redcedar, giving them good durability, and can also be supplied pressure treated with preservative for enhanced protection. In some areas, shakes or shingles are made from pine.
At the cheapest end of the market lies basic softwood boarding, coming in at around just £5-8/m². However, if left in its raw state it would deteriorate very quickly. It requires regular painting and staining and will need three coats of stain alone when it is installed. When all this is taken into consideration, it is no longer such a cheap option, which makes those timbers that require no staining or treatment, such as Western redcedar, European larch, douglas fir and even European oak, much more appealing. Cedar will cost around five times the price of untreated softwood, but will last 60 years or so with little maintenance. Larch is often now used in place of cedar or other hardwoods due to its cheaper price. The price of fibre cement boards varies, but expect to pay from around £45/m² fully installed.
Buying and Fitting
Timber merchants, online stores and cladding specialists are all options when it comes to buying your timber cladding. Some claddings come pre-treated, stained or painted, whilst others are supplied ready for you to finish — the cheaper, but more time consuming option. Timber cladding can be – and often is – fitted on a DIY basis, but if you would prefer to leave it to the professionals, then your carpenter will carry out this task. Alternatively, some of the specialists, such as Marley Eternit, offer installation services.
This type of boardinghas a uniform thickness, usually between 12-18mm, whilst widths of boards vary from 125mm to 225mm. Many fibre cement boards are square edge.
Boards are tapered across their width. This style of board produces a rustic, rural appearance that is perfect for more traditional homes, or barn-style self-builds.
Shiplap has a shaped front face and profile so that the top of each board fits behind the bottom edge of the adjacent board. It gives a neat finish. Moulded PVC boards are often avialable in this style.
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These produce a uniform look that suits contemporary houses. They have a flat face and in the absence of any overlapping, rain is kept out by the way the groove covers the tongue of the board below.
Horizontally mounted boards are preferable to vertically mounted ones as they produce greater resistance to moisture penetration. In cases where vertical weatherboarding is used, the overlap should face away from the prevailing wind.
If you’re going for a style where the boards overlap, they should do so by 30mm. Boards are fixed to battens, which should measure 50mm deep and be spaced at a maximum distance of 600mm centres. Battens should be fixed to a breather membrane or vapour barrier.
When fixing the battens, start from the bottom up and leave a distance of 150mm between the bottom edge of the weatherboarding and the ground. Each board should be fixed to at least three battens to ensure stability.