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Raising the roof on embodied carbon

Main Image 16 November 2015

By Sandy Patience, architect and editor of GreenSpec

As we continue to reduce the consumption of energy through superior design and construction, the amount that it takes to fabricate a building, the embodied carbon, becomes a greater proportion of the overall carbon equation.

Roofing

When it comes to examining materials for their environmental impact, not all is as it seems. A study of roofing materials is a good example particularly in the comparison between clay, the ‘natural’ material and the interloper, concrete.

Clay plain tiles and later, pantiles have been the vernacular roofing material of choice for generations of builders particularly in areas where clay is cheap and easily retrieved.

However, by the beginning of the 20th Century, the British clay tile industry had foundered and as the housing boom of the 1920s and 30s progressed, foreign imports flooded the yards of builders’ merchants.

For post-war architects, concrete was the new ‘must-have’ material. Concrete roof tiles achieved popularity as the house building industry became aware of the advantages of economy and buildability. Tile technologists didn’t make the mistakes of their large component cousins by ‘re-conceiving’ the product. Design closely followed the successful aspects of clay tiles. By 1960, some 80 per cent of all new roof tiles were made from concrete.

Climate Change

Just as everything in the concrete industry’s garden was looking rosy, there came over the horizon this generation’s biggest challenge - Climate Change and its prime cause, carbon dioxide.

Alongside fossil fuel burning, concrete production was identified as the worst carbon polluter.

By the first years of this century, environmentally-aware architects called into question their own use of concrete.

Carbon Reduction

Roof tile technologists had always been looking towards relieving the arduous work of laying roof tiles. Slimmer tiles and smarter interlocking mechanics made roofing an easier, safer and more economic business.

Already in the 1960s, the concrete ‘Double’ or ‘Twin’ pantile had been developed to reduce laying time and reduce the angle of pitch it could be applied to. The integral overlap design of the pantile made for a relatively straight-forward adaption to the twin format. As a result, double pantiles quickly became the top-selling roof tile.

The size was determined by it being made by hand as well as for easy handling by tilers. The tiles simplicity limits its functionality because, unlike pantiles, plain tiles can’t overlap sideways.

Innovation

Until the mid-noughties, plain tiles lost ground to pantiles. The breakthrough return came when Forticrete managed the task of designing an interlocking double plain tile that overlapped in both directions. The new tile, scored down the middle and featuring the addition of a twin camber, provided an effective resemblance of two plain tiles together.

Forticrete’s Gemini interlocking twin tile along with similar products from Redland, Marley Eternit and Sandtoft provided the market stimulus to match the success of the pantile double format.

In terms of sustainability, the real pay-off comes in two ways. Firstly, installation speed is increased as fewer tiles have to be laid per square metre – in the case of Gemini 16.6 compared to 60 conventional double lapped plain tiles. This innovation reduces the build cost and more importantly, the environmental impact. Forticrete reports that 40 % of CO2 is saved in manufacture when compared with a traditional plain tile. In addition, 40% less aggregate, tile battens, packaging and transport per roof is required.

However, if we compare the embodied carbon of clay and concrete, we discover the two materials are produced in fundamentally different ways. Clay requires firing at high temperatures for extended periods whereas concrete’s carbon bill is incurred through the cement added to the aggregate mix before curing.

The most important environmental twist comes from measuring the respective energy inputs to the manufacturing processes. In a report commissioned by Redland, Ove Arup & Partners revealed that clay tiles use around twice as much energy than concrete tiles to produce.

For once, concrete is the sustainable choice.

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