Landscape and exteriors Cladding
Avoiding common clangers Janet Sycamore identifies how to rectify issues that can affect a cladding project.
M
ost cladding issues can be avoided through careful design and installation; they can be awkward and costly to rectify once a project is complete.
Fixing faux-pas If a cladding board becomes detached from the wall or substructure, something is wrong – and it can be a mistake made with the fixing. Cladding fixings must be correctly specified and placed at specific intervals to properly secure the timber – typically dependent on timber species, board profile and arrangement. Only high-performance coated steel or stainless steel specifically designed for use on external timber cladding should be used. Unsightly black stains (iron staining) are often a telltale sign that incorrect fixings have been used. Such staining is not easy to eradicate and ruins the aesthetic – and in the longer term there is potential for the fixing to consequentially fail.
Figure 2: An example of board-on-board fixing issues. Photo: TDCA
Fixings placed too close to the board ends is also a common problem as the boards are more prone to splitting and becoming detached from the wall. As a general recommendation, fix at quarter points of board width and a minimum of 20mm in from the board end. Use two fixings at each fixing point unless the board is less than 100mm wide when one fixing can be used. Figure 2 illustrates two issues – the fixing type and the fixing placement. The black streaks are caused by using nails unsuitable for outdoor use and the top board is fitted through the bottom board, restricting movement and going against good practice recommendations.
Timber is natural and it moves
Figure 1: Standard cladding fixings. Source: TDCA
www.bmtrada.com
Wood is hygroscopic – its moisture content is affected by changes in temperature and relative humidity of the surrounding environment. This causes movement across the grain of the timber. Timber cladding should be installed with a moisture content of 16% +/- 4%. This is the mid-range for timber conditions outdoors, which can fluctuate from around 10% to 22% depending on the season. Different species have different degrees of movement and are assigned to movement classes. Ideally, cladding timber should be classed as ‘small’ or ‘medium’ movement. It is also imperative that the design and installation will accommodate the natural seasonal movement of the timber by incorporating the correct movement gaps and/ or overlaps for the profile and species used. >> Timber 2022
| 115
