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‘Chasing zero carbon targets in dense resi developments is like chasing rainbows’

Green Deal

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.

Although the zero carbon policy doesn’t officially come into force until 1 October, all major schemes not already submitted for planning should be working towards it. It will affect all projects that are validated by the GLA (called Stage 1 schemes) on or after this date and, as this happens after the local authority validation, the timeframe for this is unknown.

Zero carbon graph

Zero carbon graph

Zero carbon graph


Readers' comments (2)

  • I agree that we need to be more realistic about the actual performance of buildings, but this isn't a problem for someone else to solve. Who ought to feel responsible for a buildings final performance but the architect? The architects make most of the decisions that determine how easy or practical it is to build the building to the performance standards that are required. At least some of the blame for poorly performing buildings can be laid at the designers door for not designing a building that can be easily built to a high level of thermal performance.
    As to the realistic energy targets, what is realistic? The price of PV panels today are one tenth of what they were a decade ago, so 'realistic' is a moving target, and pressure from the GLA through what is effectively a Carbon Tax by another name, is exactly what is needed to push innovation and experimentation in the industry.
    Instead of offsetting energy elsewhere through the Allowable Solutions, can we reduce the embodied energy of the building? Can we buy in renewable energy from outside London, or even the UK? Can we recycle materials more effectively? London will never be self-sufficient in terms of its energy use, but it can be innovative in how it solves the problem of a city's impact on the planet.

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  • Completely agree with the points above, while the GLA should be applauded for raising the bar, the narrow scope of measurement and even more stringent targets, will likely lead to sub-optimal designs. While the change may encourage more innovation in some cases, in others it may lead to developers simply ‘paying off’ the LAs and inevitably passing on the additional costs to their customers.

    What is needed, is to look at carbon emissions more holistically and to use a whole-life carbon (WLC) approach - rather than targeting just one piece of the puzzle (regulated operational emissions).

    A WLC perspective considers embodied energy/carbon (as Rory pointed out), maintenance and replacement cycles as well as regulated and unregulated operational emissions over the lifetime of the building. Currently, embodied emissions are completely ignored in Regulation which means that these emissions are actually rising, both proportionally and in absolute terms (e.g. due to additional insulation etc.).
    Only with a holistic view, can you achieve a balance between operational and embodied emissions and seek to minimise carbon emissions over a building’s lifetime.

    There are various ways to implement this, which need not be overly complicated. What is critical however, is a robust calculation method that is applied consistently in order for it to gain trust across the market and go beyond simply an exercise on paper (to echo Clare’s point). We have too many of those already.

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