ModCell's straw panel walls are a carbon-friendly alternative to bricks and mortar

People say they want a low-carbon building, says ModCell's Finlay White, "but a building made from our panels will be carbon negative". With the Carbon Reduction Commitment deadline just around the corner, it's a compelling pitch. ModCell is a Bristol-based manufacturer, spun out from architectural firm White Design, originally founded by White's brother, Craig. It manufactures and supplies pre-fabricated wooden wall panels stuffed with straw bales: an environmentally conscious alternative to bricks and mortar.

"It's probably one of the most sustainable building products in the UK," explains White. It's about communities using a local resource, he adds. "When we didn't have cars, we built using the materials that were local to us."

ModCell's wall panels are manufactured from FSC approved timber, filled with locally sourced, renewable straw bales and covered with a lime render. Straw is a good insulator, explains White, which means the energy demands on the building are reduced, plus it's sustainable and stores carbon as it grows. "Each 3.2m x 3m panel has sequestered 750kg of atmospheric Co2," he says. "It stores carbon in its structure."

Straw isn't new to the building trade, but the challenge for ModCell has been to modernise and popularise its use. White says that's been like "cycling uphill in the wrong gear". The industry view, he says, is that straw is messy and flammable. "There are a lot of [wrong] perceptions," he says. "The first question we're asked is, 'surely it's a big fire risk?' But fire needs fuel, heat and oxygen," he says. And because the panels are enclosed, and the straw is compressed, "there's not a lot of oxygen in there. It's like throwing a magazine on to a fire. It takes along time to burn."

ModCell submitted its panels to a Chiltern fire test, primarily to satisfy the curiosity of the insurance industry. The wall was still resistant after two hours 23 minutes, says White. While the temperature was "1063 degrees on the side of the fire, on the other side it was between 23-42 degrees—basically a hot day in Dubai," he says.

A significant downside is cost. Straw is plentiful and therefore cheap, but the timber is imported from Switzerland (there is no comparable supplier in the UK) and the lime render comes from Germany, paid for in Euros. "Our price has gone down slightly over the last four years," argues White, "while still absorbing the cost of the Euro." Scale is still a problem, he admits. "We want to be big, but we're small at the moment. If we can scale up production, that [will] allow us to negotiate better supply costs. Currently we are at the higher end of the cost per square metre." A basic panel costs around £190 per square metre to supply and install. "It's a finished product, though," adds White.

Foreign suppliers are ModCell's one departure from environmental integrity. Every other aspect of manufacture, design and process is geared towards achieving a lower carbon footprint. That includes installing what the company calls "flying factories" close to the site in order to reduce the impact of transportation—entirely necessary when each panel can weigh up to two tonnes.

With each new contract, the company sets up a manufacturing unit within 25 miles of the construction site. This is normally on a farm, because "that's where the straw comes from", says White. This gives the farmer an income stream "he hasn't thought of", and because around 80 per cent of the labour employed to assemble the panels is local, "we put money back into the community. The locals councils love us."

ModCell works hard to keep its environmental costs of production to a minimum. "We try and make sure that all the timber arrives in one lorry and we monitor the carbon footprint of that vehicle," he explains. "If it goes back empty then we include that in our calculation of how much carbon is used to construct the building."

White says that ModCell's business model is flexible and extremely efficient. "The beauty is that with a big project we can have a number of flying factories around the construction area, within a circle of 5-25 miles, and at the end of the project we just close them down." That means no factory overheads. "So rather than a manufacturing unit sitting idle until the next project, we can say we have all these advantages for the environment and some key [cost] advantages for the business."

So far, all of ModCell's customers have been commercial, but the company is keen to add residential buildings to its portfolio. Researchers at the University of Bath are in the middle of constructing a two-storey house using ModCell panels. It is hoped that when finished, the building, known as BaleHaus, will demonstrate the benefit of carbon-negative design, and require almost no conventional heating and very low running costs.

The structure's exterior is now complete and work has begun on the building's interior. Sensors have been fitted into the walls to monitor temperature, humidity levels, air tightness and sound insulation. It's a bit early for conclusions, but researchers hope that the materials used for each BaleHaus will extract 130 tonnes of Co2 from the environment, which, after subtracting 70 tonnes for the manufacture, supply and installation, produces a net reduction of 60 tonnes-a "carbon credit" that would be enough to offset the use of fossil fuel energy for up to ten years, and for the use of over 40 years of energy from a renewable source. "A conventional house designed to today's building regulations will emit around 3.1 tonnes of Co2 a year," says White. "BaleHaus can nearly halve this to 1.6 tonnes."

ModCell is a small firm with big ideas. A possible model for the company's expansion is through licensing its technology and production processes to foreign companies. As White says, it's a low-tech design, requiring "only a screwdriver" to assemble the panels on site. If straw isn't in abundance in the host country, he adds, there are other solutions. "ModCell stands for modular cellulose," he explains, "So what about using coconut husks? Like straw it's a by-product, and you could pack it in such a way that it has the all the same advantages."

Posted 15 October 2009 : Director.co.uk