Sustainable prefab
From Sanctuary magazine issue 9.
It’s over 100 years since the first Model T rolled off the conveyor belt, but only recently since factory-assembled houses started making a splash.
To many the logic of prefab is inescapable. Mass produce a car in a factory and it is bound to be less costly and wasteful than building a unique model in your driveway. Wouldn’t the same argument apply to a house?
Architect Andrew Maynard (article) summed up the argument in a submission to the Vicurban Affordable Home Design Competition: “By far, what makes the most difference is the reduction in waste and energy that is possible through mass production, delivery, and offsite construction”.
Perhaps surprisingly then, one of the perceived benefits of prefab housing – lower cost – does not apply when it comes to sustainable building. Yes, if your idea of prefab is a plastic-clad mobile home without wheels, but definitely not if you insist on superior environmental design and materials. Sustainable prefab is not a cheaper alternative to sustainable site-built, but arguably it does offer better value for money.
The payoff for all forms of sustainable building comes with a tightly sealed, passively designed, efficiently functioning house. This leads to better environmental outcomes and lower operational costs. However the quality control inherent to sustainable prefab means you have a better guarantee of an environmentally sound house than you have with sustainable site-built.
One drawback of prefab is its lack of thermal mass. A site-built house that employs passive solar design with concrete slab floor or rammed earth wall will retain winter warmth and summer cool much better than a house which doesn’t have those things. Quality prefab partly compensates for this with extra insulation, but it’s something that must be borne in mind.
One way around prefab’s lack of thermal mass is to build or retain a massive (that is, weighty, high thermal mass) element on-site and couple prefabricated modular elements with it.
On the other hand, if you think you can live without the thermal mass, there is a lot to like about a house that employs a deep pile foundation as opposed to a shallow slab foundation. One touches the earth lightly, the other does not.
In Australia we still seem to equate prefab with cheap holiday homes. It’s time we did away with that image. Ecoshelta’s pod design (article) looks just as at home in inner-suburban Sydney as it does on Flinders Island. Modscape’s “overdesigned” steel-framed modules (article) are strong enough to stack seven storeys high, meaning they could easily become a steel-framed block of flats. Sustainable prefab is here to stay. Hopefully we’ll be seeing more of it in our cities. This is definitely not the last you’ll see of it in Sanctuary.
