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Box 21 The Case of Steel-Frame Housing
Despite their impressive advances, there are many examples of life-cycle analyses that take a
narrow perspective. A whole systems analysis would look at the life-cycle of products, pro
-
grammes, buildings and materials – but also at geographically specific ecological factors, such as
biodiversity, environmental flows and ecosystem integrity. To take a case in point: steel-frame
housing has been advocated on grounds of long life and durability. The Australian Greenhouse
Office was promoting steel frame housing at one stage because they discounted the embodied
energy of materials. But again, if buildings used passive solar heating, cooling and ventilating,
then embodied energy would be the more critical issue.
1
Yet even this ‘narrow’ life-cycle ap-
proach presents unresolved, complex issues:
•
A timber-frame house stores almost three times more carbon than a steel-frame house,
and production of the steel-frame house releases about five times more CO
2
than
a timber-frame house. Therefore, energy and pollution reduction through recycling
may be less important than a shift from fossil fuels to solar energy and, ultimately,
to a ‘carbohydrate economy’ (ie an industrial system where carbohydrates replace
hydrocarbons, that is where vegetables, not minerals, supply factories for fuel and
particularly materials).
2
Growing materials may be better for the environment than
mining them.
•
Steel has at least 20 per cent more embodied energy than timber (the steel industry
alone uses as much electricity as the residential sector).
3
A timber-framed building
takes six years of operation to consume the same amount of energy as that used in
construction, while a steel-framed building takes about nine years. Although steel is
increasingly ‘recycled’, the recycled content is often still small compared to that of ‘virgin’
ore. Organic materials are generally less harmful to produce than minerals, and can be
composted at the end of their life rather than being transported to landfill.
•
The longevity of a structure often depends on the least durable
component
. The lifespan
of housing is shortened by many factors other than the strength of the steel frame. Steel
framing, for example, can be subject to moisture problems in walls. Like timber frames,
they are susceptible to mould damage if not properly moisture- and vapour-proofed
(although not as vulnerable to termites). Mould damage is a billion dollar issue in San
Francisco, for example. In such cases, steel would not be likely to realize its potential
lifespan.
•
The electromagnetic field implications of steel-frame are still under investigation and
could have long-term public health consequences, although some consider this highly
debatable. Few take this potential problem seriously, but nor were the effects of radon
or microwaves taken seriously at one time.
4
The precautionary principle suggests it is
not
advisable to lock society into a permanent construction system that might have long-
term health impacts and lose opportunities for future adaptation and innovation.
•
The insulation value of steel framing is around 30 per cent lower than wood
construction. Steel members can cause ‘thermal bridging’, where hot or cold leaks
through an insulated wall via a highly conductive material. Materials with better insulative
properties are available that are cheaper, locally produced and have lower impacts, such
as strawbale or earth construction. These can be combined with steel framing, of course.
•
While steel can be designed for disassembly, steel structures also lock us into building
systems and aesthetics that might become obsolete or otherwise unsuitable in changing
times (‘11 September’ was hopefully a learning experience for urban designers among
others). On a smaller scale, the long spans possible with steel allow internal walls to be
easily rearranged to accommodate changing user needs, but timber lattice space frames
can also enable high spans.
5
Some of these issues cannot really be determined by numbers. It is too easy to advocate – or
object to – steel framing without a whole systems analysis that takes into account a broad range
of criteria and recognizes changing needs, values and contextual factors.
6
The built environment
is a complex system, and this is before we try to factor in the ecology.
303
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