Sustainability And Lightweight Roofing

By Graham Hepburn
Advances in technology over the years have meant that metal roofs have not only become more durable but also lighter.

Metal roofs have always been lighter than concrete tiles or slate but they have been refined to become progressively lighter over the years. The advent of longrun roofing – rather than using overlapping 3- metre-long sheets – has cut weight and waste but the invention of high strength steel coil has helped metal roofing to become even lighter.

Steel coil is now about twice as tough (tensile strength) as the softer steels previously used, meaning thinner gauges can be used. This dramatically cuts the amount of steel needed and makes for a much lighter product. The typical gauge now used in longrun, for example, is 0.40mm, nearly 30% thinner than 0.55mm which was traditionally the thinnest gauge available. This lighter product is not only more durable because of improved Zincalume® substrate and paint systems but easier to transport and takes less framing to support – reducing waste on several fronts. A recent analysis by an independent consultant showed that the framing for a lightweight metal roof was cheaper and easier to erect than that for a heavyweight roof such as concrete tiles or slate. For a 300 square metre home, the study showed that installing a lightweight metal roof could result in a saving of $3000. On average, a heavyweight roof structure would require an extra $2000 worth of framing materials and $1000 more in labour costs. The study also pointed out that the structural cost savings on a lightweight metal roof will increase as more gables are added to the roof design.

A metal roof compared to a heavy weight roof uses less energy (less carbon) to transport because of its reduced weight and doesn’t require as much framing. A typical truck can carry enough metal roofing for about ten homes while only one house lot of concrete tiles would fit on the equivalent truck, because of the tiles’ bulk and weight. These increased transport costs mean heavyweight roofing becomes less competitive as the distance between factory and building site grows – not to mention the increased carbon emissions involved in carrying heavyweight roofing significant distances. This has a huge impact on the overall sustainability of the building material component of the building.

Because a metal roof is lighter – down to a tenth of the weight of concrete tiles – it isn’t prone to settling or sagging which heavyweight roofs can be subject to over time, reducing the risk of doors or windows jamming or cracks in claddings occurring which could then be prone to water ingress.

As well as structural cost savings, lightweight roofing provides added design flexibility and can be used on any structure as part of a re-roof.