Building control in Australia: extreme weather

30 March 2017

Continuing his series from Australia, Mark Anderson looks at the repercussions of extreme weather

Each year, buildings are lost to extreme weather conditions and natural disasters in most parts of Australia, but in particular the Northern Territory and Queensland.

Losing homes and possessions can involve long-term financial and emotional hardship, especially for households that are either underinsured or not insured.

Damage can include:

• failure of corroded connector fasteners to plates, to roof battens and to other components;
• failure of rotten timbers;
• garage doors being blown in or out;
• roofs blown away in whole or in part;
• collapse of unreinforced masonry walls;
• collapse of poorly built housing that is located on exposed sites such as hills and sea frontages;
• flying debris breaking doors and windows, causing further damage from water leakage and allowing wind into the building;
• doors and windows blown open due to inadequate fixing to walls or inadequate locks;
• water leakage in ceilings and walls;
• failure of building attachments such as guttering, fascias and eaves;
• fallen trees.

Cyclones and winds

Houses built before the mid-1980s in Queensland and Western Australia or before 1975 in the Northern Territory may not be constructed to cyclonic building standards and therefore may not be able to withstand such winds.

No building can be made entirely cyclone-proof but you can take appropriate structural measures

Cyclone Tracy hit a vastly unprepared Darwin, the Northern Territory capital, in late 1974, demolishing around 80% of homes and necessitating evacuation of 47,000 residents; 71 lives were lost.

Given that some areas in Australia are more prone to such catastrophic natural events, as well as bushfires and earthquakes, the Australian Building Codes Board introduced advice for these localities, the goal of which has been to keep properties and their inhabitants safe over the past 30 years.

Scientists worked with government to ensure that these would help mitigate the effects of such natural catastrophes. This means that today we have codes for wind compliance for all coastal areas in Australia.

When a cyclone hits, it causes damage to the building and may lead to its collapse if it gets inside, with pressure building up beneath the roof and ceiling that results in them being lifted up and pushes the walls out.

One way to combat this is to prevent wind entering the house, and if this not possible then to have provided extra strong fasteners to secure the roof. Walls and ceilings should also be braced with additional plywood boarding to reduce the effect of wind.

Wind load

A coastal location can influence how you mitigate the effects of strong winds. When calculating the wind load of a site, you should consider the following factors:

• mature trees;
• site elevation;
• other buildings that may offer protection or pose a risk if fixtures become detached.

Mature trees can shield a new development, as can other buildings. The higher the site the more likely it is that the wind will have an adverse effect. A house that is isolated on the top of a hill, for example, is going to have a higher wind load than one in the valley, and the higher that load, the greater the need to provide additional wind bracing and fasteners.

Maintenance is a key issue for homes in regions prone to cyclones and strong winds. Even those that have been built to code can be damaged or collapse if they are allowed to deteriorate. According to Northern Territory government publications, dwellings and buildings such as garages and sheds need to be regularly checked for corrosion, rot and attacks by termites and other insects, as they should for general weathering.

Cyclone-resistant fabric panels that are polymer-based add trampoline-like coverings to windows and doors to repel flying debris without sacrificing visibility in a storm. These are secured to the edges of windows and doorways with grommets and wing nuts or clips and pins, making them easy to install and remove.

Residents of areas that are prone to cyclones and strong winds should have a safe place to shelter on their property. This should be a small room with reinforced concrete walls and a concrete ceiling if possible. If the walls are not concrete, you should consider additional strengthening measures in that room. In other parts of the world you would provide a basement, but these are not common features of buildings in these areas of Australia. Nevertheless, providing this room is a cost-effective way to ensure that you can survive such catastrophic events.

It should be stressed that no building can be made entirely cyclone-proof. However, you can reduce the effects of such weather events by adding the structural measures that are appropriate for your location and maintaining your building to a good standard.

Engaging a qualified practitioner such as a building certifier, structural engineer, architect or builder to inspect your house remains the best form of prevention.

Mark Anderson is a senior building certifier at KPMG SGA.

Further information

This feature is taken from the RICS Building control journal (February/March 2017).