The next great bandwagon: eco accounting

The voluntary Code for Sustainable Homes comes into force in June, and the clever money in housebuilding hopes it will provide some guidance for at least the next decade.

Forget the concerns that we are building too few houses and flats. Let’s start designing and building “sustainable” homes. OK, so they’ll only account for 0.75% of Britain’s total housing stock. But as homes continue to be in short supply, the property market, which comprises mostly the 25.5m existing, carbon-emitting homes, will carry the niche market in new “sustainable” homes.

The BRE is fleshing out the Code for Sustainable Homes point scoring system that will effectively replace its now defunct Eco-Homes standard. It will publish the technical document in April, and many designers will breathe a sigh of carbon dioxide. Assuming the Department of Communities and Local Government decides what “zero carbon homes” means this year, of course.

The German Passivhaus standard from the 1990s, is the benchmark. That is a U value of 0.15W/m2K which requires an air-tightness of 1.0m3/hr/m2, potentially reducing the total energy demand for space heating and cooling to 15Kwh/m2/year, while ensuring the occupants have “enough” fresh air. But putting a two-computer household, with the kids’ PlayStations and mobile phone rechargers inside a low energy envelope might frustrate the exercise.

Housing minister Yvette Cooper is not yet suggesting “sustainable” homes should be policed in their operation as a condition of planning approval, but David Miliband, secretary of state for environment, farming and rural affairs, is working hard in the direction of personal carbon rationing.

Consultants, who had only recently learned to speak MMC, have switched without blinking to philosophical discussions about carbon accounting. What should be the arbitrary level of building performance against which the well behaved family’s “savings” in carbon are measured? What on earth will Kelly’s DCLG do with existing housing? Oh yes… set up carbon rationing as a financial conversion of carbon “savings” into a tradable commodity, and put a carbon cap on owners of older homes.

Consultants who had only recently learned to speak mmc have switched to discussions about carbon accounting

While these imponderables will be regulated as an inevitable consequence of trying to save the planet at the point of energy consumption, buildings still have to be produced. The practical issue at the end of the eco-accountancy will be inescapable.

Take a rectilinear two-storey detached house of 6.3 m x 8.1 m. When walls were 9in, or 225mm, in solid brick, the gross internal floor area might have been around 88% of the gross external area, ignoring the subtleties of stairs and partitions. The technological innovation of cavity walls and insulation, sometimes with the substitution of timber or steel frame for load-bearing masonry with its thermal mass benefits, have all brought walls to around 300mm. That is a gross internal of 85% of gross external, in a very simple typology, with a U value of around 0.35W/m2K. To get down to passive house standards using fibrous or foamed insulation the wall thickness will go up to and beyond 400mm, with gross internal being 80% of the house perimeter.

The building is growing in bulk and cost per m2.

Until insulation performance improves by a factor of at least 10, as it has in other industrial sectors, expensive walls at one fifth of the building footprint, and denser site layouts due to speculative land values, will combine to reduce useable floor area. The maths gets worse as space gets smaller in zero-carbon homes, before stairs and partitions are discounted.

Planning Policy Statement 3, published last November, is imagined to relate residential topologies to Britain’s part in combating global climate change. Of course, it does nothing of the kind. What about the connecting math between the technology of house building, household behaviour, demographic demand for more and larger house types, a property market that doesn’t care, a Treasury that cares about the property market, a planning system defined by making developable land scarce, Britain’s insignificant industrial contribution to the world, increasing financial speculation in the global carbon economy, and the uncertain science of stabilising the weather on a living planet within the solar system?

Stop asking awkward questions! The way to save the planet is through creative eco-accounting, one home at a time.