How to sidestep typical errors in timber cladding detailing

 Tuesday, May 7, 2024

In construction projects, precise detailing is really essential, particularly with timber cladding, where the focus on detail becomes a critical issue. No matter the timber species or its durability class, faulty detailing can cause problems ranging from cosmetic defects to severe structural damage, such as rot. Water management is a primary consideration, as its infiltration can drastically affect the timber’s performance and longevity. Proper detailing facilitates water runoff from both the cladding and its underlying structure, promoting natural ventilation and minimising water retention.

Architectural Liason Technician, Ross McCormack, enlightens on the common detailing in timber cladding and provides practical solutions to avoid unnecessary hazards by ensuring longevity.

1. Common oversight: Flat edges in cladding arrangement

Creating horizontal flat edges within the cladding arrangement or substructure can create areas where water accumulates, leading to the area remaining constantly wet and resulting in rot.

Traditionally, this has occurred with non-sloped horizontal battens and square-edged open rainscreen boards being used horizontally. More recently, we are seeing a trend for larger on-edge horizontal sections of cladding being used as a break between floors or a form of casement at the top and bottom of cladding. Incorporating flashing with a drip point located at least 35mm from the front face of the horizontal section helps facilitates water runoff.

Top tip from Ross McCormack: Avoid horizontal sections at the lowest point of a cladding arrangement to minimise the risk of water pooling.

2. Common Oversight: Cladding proximity to ground

Installing cladding too near to hard ground surfaces can lead to complications, though these can be mitigated with minimal design alterations. The primary issue arises from impact water—rainwater that rebounds off hard surfaces like patios and strikes the end grain of the cladding boards.

Being close to the ground can increase the likelihood of debris such as leaves and grass clogging the essential 10mm ventilation gap at the bottom of the cladding, trapping moisture and potentially leading to rot. To prevent these issues, it’s important to maintain a minimum ground clearance of 150mm for the cladding. For optimal performance, a clearance of 200mm is recommended.

3. Common oversight: Substructure ventilation behind cladding

Ensuring adequate ventilation behind cladding boards is crucial for regulating moisture levels and averting rot. The substructure of the cladding can accumulate moisture through condensation, water ingress, and standing water. Without sufficient ventilation, this moisture can build up, unable to evaporate, thus elevating the moisture content to levels that could compromise the integrity of the structure.

Pro tip: Avoid using covering materials that hinder ventilation or trap water between the outermost batten and boards, such as breather membranes, insect mesh or OSB.

4. Common oversight: Interaction between timber cladding and metals

Many people are unaware that timber cladding is naturally acidic, typically exhibiting a pH between 3 and 5. Timber species with a pH of 4 or lower can be corrosive to metals. The degree of corrosion varies, with some metals being more vulnerable to this effect than others.

If using metals below timber cladding, like flashing or roofing, they advise using a metal that has a slight or insignificant susceptibility to corrosion, such as powder coated aluminum or stainless steel.

Read more news on: Timber, timber cladding, woodworking

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