She'll be right – my house is 'cyclone coded'
The Insight
Cyclones pose a very real threat to communities across coastal areas of northern Australia. This isn’t news; people living in these areas are aware of the threat and there is frequent talk of buildings, particularly houses, being ‘cyclone coded’ – but what does that actually mean?
The term ‘cyclone coded’ and the way it is used amongst the general public seems to indicate a binary choice. Your house is either cyclone coded or it isn’t. It is suitable to be used as shelter during a cyclone, or it isn’t. As with most things in life, the reality is actually far more nuanced.
Using current design standards, the wind speeds to be considered by engineers are driven firstly by the importance level of the building as defined in the National Construction Code. To go a little into the detail that makes the eyes of most glaze over, houses are typically Importance Level 2. This requires that they be designed for a statistical 1 in 500 year wind event. In cyclonic regions across the Northern Territory, Queensland and the north of Western Australia, this is a basic wind speed of approximately 250 km/h – the equivalent of a mid-range category 4 cyclone.
Does this mean that higher wind speeds will result in wide spread structural damage, while lower wind speeds mean everyone will be safe in their ‘cyclone coded’ houses?
Maybe.
The Impact
The extent of damage is dependent on factors other than wind speed including the duration of the cyclonic event and condition of your house, as well as the integrity of surrounding structures and the general tidiness of the community which both impact the resulting wind-borne debris loads.
Over the years, there have been significant improvements in building practices to ensure buildings are more resilient under high wind loads. Examples include improvements in roof fixing details and the increasing use of wind locks in roller door tracks.
The improvement in roof fixing details unsurprisingly reduces the loss of roofs in high wind events. Failure of roller doors typically results in additional uplift loads on roofs caused by the influx of wind into the exposed space. Therefore reducing roller door failure also reduces the loss of roofs. Both these measures increase the safety of the occupants considerably.
Additionally, we bear responsibility for improving the safety of our houses during a cyclonic event by maintaining them in a good condition. When undertaking repair or replacement works to elements such as roofs and roller doors, we must ensure these works are appropriate for our environment. We also need to undertake thorough pre-cyclone clean-ups to reduce the potential wind-borne debris load.
When talking about the safety of your house during a cyclone, knowing whether it is ‘cyclone coded’ is just part of the equation.