Arguments about what really constitutes sustainability can be heated and founder on a lack of documentary evidence. This is why an earth-sheltered building designed by environmentally conscious architect Jerry Harrall is so interesting and important. He has designed a house for himself and a small office for his practice SEARCH (Sustainable Ecological Architecture) on the principles of low embodied energy, high thermal performance and minimal environmental impact.
The building will form the basis of his doctoral thesis, and he is monitoring the hell out of it.
'On completion of both buildings, we'll monitor them for 12 months at least for the purposes of the doctorate, ' Harrall said. 'We believe they might be the most monitored buildings in the UK - there are 120 temperature monitors built into them and we're monitoring the performance of the superstructure and the earth every hour, every day, 12 months of the year, indefinitely.'
The 180m 2house and 54m 2office should require no energy for heating, create no net CO 2contribution and have a quarter of the running cost of a conventional building. In addition, all materials and methods have been chosen to have as small an environmental impact as possible. One of the essentials of the design is the use of an 'offthe-ground' substructure. This consists of a reinforced slab that acts as foundations and floor combined. 'Unlike a raft, it is rectangular in section throughout its plane, ' said Harrall. Environmentally the advantage of this approach is that no excavation is necessary. The slab sits directly on hardcore, supported by compacted earth. And to create a key between the soil and the hardcore, there is a capping layer of 100 tonnes of brick batts, an aggregate made by Hanson Brick from recycled brick waste.
Concrete is used extensively in the building, with walls of 300mm dense concrete blocks and in-situ concrete. Harrall is concerned about the fact that for every m 3 ofcement produced, a tonne of CO 2is generated. Minimising the cement content was therefore a priority. In this case, 10 per cent was replaced with very finely ground brick waste supplied by Hanson - the same material as the brick batts but the product of a further milling process.
Steven Miller, Hanson Brick's technical director, said: 'It has actually recreated a very old type of cement developed by the Romans. They used to grind up the waste from clay-pot manufacturers and mix it with burnt lime to achieve the same effect.'
The product was developed by Professor Stanley Wilde and Dr Martin O'Farrell at the University of Glamorgan's School of the Built Environment. O'Farrell's PhD was sponsored by Hanson Brick, which is how the company came to take such an interest in Harrall's work.
'This is the first time low-embodiedenergy concrete has been used, ' said Harrall.
All the materials were available from near to the South Lincolnshire site, minimising the environmental impact of transport. Theoretically more of the cement could have been replaced with brick dust - in experiments substitutions of up to 30 per cent have been used - but because this was a live building project, Harrall was cautious.
There were some problems of workability. 'The brick dust 'muddies up' the concrete, ' Harrall said. 'We used a lot more water and increased the slump.' The design strength was 30N but at 28 days slump the concrete was found to have achieved 50N.
The experiment has been as successful aesthetically as technically. 'The concrete looks stunning, ' said Harrall, 'it has a red hue to it.' In addition a quartzite aggregate was used, creating a terrazzo effect when the floor slab was polished.
The building does also use real, whole bricks. There are loadbearing masonry piers at the front that use 5,000 bricks - Victorian Blue bricks from the Butterley range, made in Buckley, north Wales, and yellow Hampton Autumn Mixture bricks, made at Hanson's King's Dyke factory near Peterborough. The latter range contains two recycled materials: ground granulated blast-furnace slag from Scunthorpe, a by-product of steel manufacture, and wood chippings from makers of chipboard furniture. These bricks are actually of higher specification than if they had been made purely from clay.
Not surprisingly, the building is highly insulated, with 140mm of extruded polystyrene used on the roof, the walls and under the floor. This is equivalent to 240mm of expanded polystyrene and has the additional important benefit of having a water take-up of only 5 per cent, so maintaining its thermal performance.
Harrall is confident that the house will need no heating, although there is an underfloor heating system that will be triggered thermostatically in extreme conditions.
Once the monitoring process is complete, we should know just how successful this approach has been. If his ideas take off there should be a wider market for the innovative products Hanson has helped develop.