Leave it to us

It took a long time to engage politicians with the carbon movement. But when they started to move, boy, did they move! In recent times local government, led by the mayor of London, has driven a more progressive carbon agenda through its planning processes than central government through its regulations. In London, if you get planning permission you can be pretty confident Building Regulations Part L approval is in the bag.

But it seems central government is back in the race. The construction press has been full of the demands of the Housing Minister, Yvette Cooper, who is using the upcoming Code for Sustainable Homes to out-stipulate a heavily conditioned planning consent on the carbon targets for a major London residential scheme.

The code applies progressive and steep cuts in carbon footprint, with zero-carbon homes required in 2016. It seems the Home Builders Federation has signed up, subject to clarifications – not least the definition of zero carbon.

The working definition is a net balance, meaning homes can import carbon-based energy provided they displace the same amount at other times by renewable energy exports. I wonder how this will work? What are electricity suppliers meant to do with a vast surge of homespun electricity into their mains on a lazy Sunday when the day before they faced the spike of 20 million kettles as the half-time whistle blew on the Cup Final?

Demanding that households be zero carbon at their threshold is to miss the essentials of the law of diminishing returns: that the cost of achieving the last 20% cut to zero will likely be as much as the first 80%. A standard new house produces less than 50% of the emissions of an older one but, being at the start of the curve of diminishing returns, at little cost. The cost of the “last 20%” using embedded technology is about £25,000. Surely the government must see this could jeopardise its target for 200,000 new homes every year? We only build 165,000 at the moment.

What will suppliers do with a vast surge of homespun electricity into their mains on a lazy Sunday?

If today, and for every year hence, we build 200,000 of these zero-carbon homes in place of the current model, the net effect on the UK’s emissions would be to cut about 1.5 MtC/annum (1%) by the "Year Zero" of 2016 – at an added cost of £50 billion. The UK would invest about £1500 for each tonne of carbon saved by embedded zero technologies.

If, however, the definition of zero carbon admitted other measures – such as offsite renewables generation or offsetting – then, because investment in the final 20% would be directed at lower hung fruit with better yields, zero-carbon homes could be rolled out at a fraction of the premium cost, with the same outcome. The goal of 200,000 new homes a year would look more likely. And, because the cost of these other remedies begins at less than 5% of the price of embedding renewable technology in homes, development consent deals could be struck around negative carbon outcomes. Then we’d really see inroads into the national carbon footprint.

Of course this may be complex to administer, but the civil service is good at admin. Plus, with well audited offsetting, the government might find it’s far easier to validate offsets than to enforce carbon regulations at the front door of every new dwelling.

Widening the definition of “zero” will have other gains. We would see more balanced investment between energy supply and demand sectors. The demand for cost-optimised new dwellings would increase the rate at which inefficient old housing is replaced. And good new “80%-of-the-way-there” housing won't disappear; as expensive bolt-on, zero-carbon technologies evolve into best buys, they too will be retrofitted.

So politicians, thank you for joining the carbon agenda and for your massive impact on the mission. By all means set challenging targets – but please don’t tell us how to meet them. And remember that economics is a fundamental of sustainable development.