design
mag |
89
A bushfire is probably the most severe test of any
house.The roofing material and structure are vital
components in this equation.
Following comprehensive fire testing by Exova
Warringtonfire Australia, tiled roofs are approved for
use in areas designated Bushfire Attack Level –
Flame Zones (BAL-FZ), the highest level of bushfire
risk. Like all roof systems, their use in these areas is
subject to bushfire-zone-specific construction
requirements. However the requirements are not
onerous and can be carried out using
conventional tools and techniques.
The high density and thermal mass of roof tiles
provides enhanced protection from radiant heat
during bushfire attack.This same mass also offers
greater resistance to wind suction than lightweight
metal sheets.As has been seen so often and so
tragically, extreme wind suction during a bushfire
can lift sheets or strip an entire metal roof in
seconds.
The full fire testing report and a technical guide for
builders and tilers working in bushfire-prone areas
can be downloaded from
.
Solar absorption – the amount of solar
energy absorbed by a product – and solar
reflectance – the amount reflected – are
interlinked.That is, if 20 percent of the solar
energy is absorbed, then 80 percent must
be reflected.The absorption and reflectance
of roofing materials has also been
compared at the Florida Solar Energy Center
which measured the performance of
different materials of similar colours.The tests
compared a white barrel-style concrete roof
tile with a standard white standing-seam
metal roofing sheet. Concrete roof tiles
again proved to be the superior performer,
reflecting 7.8 percent more energy than an
identically-coloured metal roofing product.
This has important implications in the design
of so called “cool roofs” which are discussed
in the sidebar to this article.
Bushfire housing –
build with confidence
Solar absorption & reflectance –
the results might surprise you
White concrete roof tile White sheet metal
Source: Parker, D & Sherwin, J, Comparative Summer Attic Thermal Performance of Six Roof Constructions, Florida Solar
Energy Center, University of Central Florida (1997)
).
24.6%*
Absorbed
32.4%*
Absorbed
Reflected
Reflected
75.4%*
67.6%*
24.6%*
Absorbed
32.4%*
Absorbed
Reflected
Reflected
75.4%*
67.6%*
