||It has been suggested that Stone cladding be merged into this article. (Discuss) Proposed since December 2015.|
Cladding is the application of one material over another to provide skin or layer intended to control the infiltration of weather elements, or for aesthetic purposes. Cladding does not necessarily have to provide a waterproof condition but is instead a control element. This control element may only serve to safely direct water or wind in order to control run-off and prevent infiltration into the building structure. This is also a control element to prevent noise from entering or escaping. Cladding applied to windows is often referred to as window capping and is a very specialized field.
Timber cladding provides a highly attractive and durable external finish which is renewable, reusable, biodegradable and contains minimal embodied energy.
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. Due to its low resin content it can be readily stained or painted. 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 (the durability can be a little lower than that of imported).
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 but can require pre-drilling before installation with screws or nails. 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.
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 extremely durable, but it should be ensured that the timber comes from a sustainable source.
Some cladding product come with 15 years guarantee and are endorsed under a scheme such as CladMark from the Timber Decking And Cladding Association (TDCA).
In addition to these choices are an emerging group of thermally modified wood products 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 promote the sustainable benefits, with thermally modified softwoods offering a good alternative to depleting tropical hardwoods.
- Fleming, et al., The Penguin Dictionary of Architecture, p.76 (1980)
- Nik Vigener, PE and Mark A. Brown. WBDG http://www.wbdg.org/design/env_fenestration_cw.php. Missing or empty