Steel frames are non-combustible (AS1530.1), and can thus significantly reduce the amount of flammable material in the average house.
In bushfires, many homes are lost because flying embers enter the roof between tiles igniting combustible materials, including timber trusses. Steel framing and steel roofing (which is fixed from ridge to eaves in long, continuous sheets), helps prevent this scenario from unfolding.
Steel frames are also electrically safe. The frames are independently earthed, ensuring that in the event of an electrical fault or a lightning strike, the current is drained directly to earth. In addition, all electrical wiring must pass through swaged holes in the frame or through insulating grommets inserted in plain holes.
Safer than Timber if struck by lightning
A common myth is that steel framed or roofed houses are more subject to lightning strikes than brick or timber and tile houses.
In principle, there are theoretical grounds for believing that metal structures are slightly more subject to strikes than non-metallic structures, but there is no evidence to support such a belief.
In practice buildings made from insulating materials appear to be just as susceptible to strikes as buildings made from metals. The reason is that even insulators conduct electricity well enough to promote strikes.
The energy involved in a lightning strike is huge, and any object which absorbs this energy will heat up during the 100 milliseconds or so of the strike. The temperature rise can be so great and so rapid that any water or other volatile components are vapourised virtually instantaneously, causing a destructive explosion.
Steel framed/roofed houses are safer than brick/timber houses because steel is a good electrical conductor, so the power dissipated in a steel roof or frame is much less than a timber or brick structure of similar size.
Thus the temperature rise is much lower. In addition, steel is not permeable to water, so there are no low temperature volatile components to explode.
The best protection is afforded by a metal roofed, metal clad, metal framed building, in which all the metal components are electrically bonded and earthed. This fact is recognised by the insurance industry, which offers discounts for such safe structures.
All steel framed houses are earthed when erected. If lightning strikes the electrical current is conducted through an earthing device to ground.
The real cost advantage
In terms of cost, steel framing is today more competitive than ever. This is a direct result of the development of the 'new era' light weight framing and truss systems and the expansion of the pool of experienced tradespeople who are working with steel. However, the real comparative cost is increasingly being viewed not just on a cost-per-square-metre basis, but on the cost of call-backs. On this basis, steel stands up as a strong proposition - both for builders and consumers.
An additional benefit for the homeowner is that steel house framing can also provide substantial insurance cost savings. The MMI Steel-Shield insurance package was developed specifically for builders and owners of steel framed homes, and provides recognition of the inherent strength and safety of steel framing through reduced insurance premiums.