Top Four Considerations When Detailing Timber Cladding

Here’s how to keep external timber boards looking as good as the day they were applied, with careful detailing and appropriate finishes to protect from wind, rain and sun.

Much like a human being, the longevity of timber weatherboards comes down to how well they are looked after and their exposure to the elements. However, much of how quickly and completely this occurs comes down to how well the design was detailed before the build took place, as well as the level of protection and maintenance the timber receives. Preventing moisture from seeping in is one of the best ways to retain stability - and there are many ways to ensure this.

1. Give your board ends some space. The end grain of a timber board is most susceptible to moisture build up. That’s why it is common to see water damage growing from the ground up on vertical timber weatherboards. Ensuring the end of the timber doesn’t butt directly into any surface, including window heads, is the best way to prevent this. Bottom edge clearance of 5-10mm will reduce this, with a 15 degree angle to the surface below, to allow water to run off and prevent pooling. For weatherboards close to ground level, you will need 175mm clearance from any earth and 100mm from paving to allow for significant rain events. For further protection, apply an end sealer, which will close off the end grains with a waxy layer of protection, minimising water penetration.

2. Ventilate your cladding. Allowing space for airflow behind weatherboards will give any moisture that gets through a chance to dry out before damage can be done. Alongside a cavity between boards and sarking, a 10mm spacer will allow for water to run off behind boards, and a 15 degree angle to the rear of the board will prevent pooling between them and protect the bottom edges of the board.

3. Optimise your flashings. Sufficient parapet flashings will reduce moisture from entering from above. This protection is also important at the bottom edge of windows, which can accumulate water that will drip down to the weatherboards below. Again, a slight angle is recommended to allow the moisture to fall away, and weatherboards should continue under the window edge, rather than beginning just below it, so that the timber ends are not exposed to this moisture.

4. Specify low movement timber. Timber will naturally shrink and expand over time, which when applied to a building will lower its weather tightness. To minimise movement when water goes into and out of the timber’s cell wall, Abodo Vulcan products are put through a thermal modification process, removing water and tannins from the cell walls and then collapses the cell walls. This process prevents moisture from entering through the outer cell walls of the wood in service and stops any changes in temperature from affecting its stability.

For more information and clear, concise images of best practice detailing, visit our Resources page and download our suite of CodeMark (NZ) CAD drawings.