It is practically impossible for high-density housing schemes to achieve zero carbon targets on site, says Clare Murray, head of sustainability at Levitt Bernstein
From 1 October 2016 a new clause in the GLA’s London Plan Policy will call for residential developments to become zero carbon, going beyond the 35 per cent reduction in regulated CO2 emissions currently required through on-site measures and now carbon offset payments to the local authority, too.
The GLA has taken the lead in this area to push the boundaries of construction, encourage sustainable design and assist in meeting future carbon targets – all of which are key to London’s future development. It was only last year that the government scrapped its Zero Carbon Policy and so the GLA should be applauded for setting the bar high and pursuing it.
But for the developers and design teams trying to build new homes in London, the target set is only as good as the calculation methodology backing it up. The question is: how much of this will be achievable on site and how much will need to be met through the new offset payments? To work this out we are left at the mercy of the Standard Assessment Procedure (SAP); the Building Regulations Part L calculation methodology.
Essentially, SAP calculations are a simplified and standardised way of estimating energy use in a home. In some respects they can be considered detailed enough, for example in the measurement and geometry of dwellings, but in other respects the models couldn’t be further from reality. Predicted system efficiencies often far exceed those installed and combined heat and power plants (CHP) included in the calculations often don’t get switched on. It is these gaps between design and reality which render the CO2 reductions on paper meaningless and prevent the best outcome for residents and maintenance teams.
Regardless, these models are used to determine a development’s performance against zero carbon and therefore how much money is required in offset payments. So, if meeting Building Regulations Part L1A equals a 0 per cent reduction in CO2, then the building design and systems need to do something pretty special to make it to 100 per cent (zero carbon).
The fact is, zero carbon is a near-impossible target for high density housing to achieve on-site. Pushing the building fabric to extremes (near Passivhaus, say) might only get an apartment building a 10-15 per cent reduction in CO2 over Part L 2013, leaving the remaining 85-90 per cent to be reduced from efficient and renewable technologies. A problem then occurs when the low-carbon technologies are not efficient enough and there is not enough space on the plot for the renewables to offset the remaining energy consumption (assuming the site doesn’t have a spare field nearby for photovoltaics!).
So why are we still specifying and installing inappropriate technologies to satisfy a crude hypothetical calculation methodology that was never designed for this purpose? It does not result in good design, nor does it make homes sustainable places to live. Would it not be better to focus on designing homes that are thermally comfortable in summer and winter, lit with natural daylight and with realistically low energy bills and carbon emissions? It is time we overhauled the crude calculation methodology that is SAP, and targeted more meaningful design measures that enhance building performance in reality. After all, we are trying to reduce carbon in the real world, not on a piece of paper.
How much will the offset payments cost?
From 1 October 2016 the London Plan Policy 5.2, ‘Minimising carbon dioxide emissions’, will seek for major residential projects to achieve the new zero carbon target. Despite the scrapping of the Zero Carbon Policy by the government in 2015 after the Housing Standards Review, the GLA is pressing on.
This means that new developments of more than 10 homes should seek to reduce regulated carbon emissions beyond the currently required 35 per cent and head for zero carbon. This can be achieved through a mixture of on-site measures including fabric improvements, efficient energy supply, installation of renewable technologies, and a new measure: offset payments to the local authority too.
The payments to meet zero carbon are suggested to be £60 per tonne of CO2 for a period of 30 years, which equates to £1,800 per tonne of carbon not reduced through on-site measures.
To put this into context, a recently approved scheme of 300 homes which met a 35 per cent reduction in CO2 would now be required to pay the remaining 65 per cent reduction, totalling over £485,000, or about £1,500-£1,800 per home.
Zero carbon graph