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Academic paper review: “An investigation into recent proposals for a revised definition of zero carbon homes in the UK”

by Mel Starrs on April 29, 2012

in Passivhaus, Zero Carbon

McLeod, R.S., et al., An investigation into recent proposals for a revised definition of zero carbon homes in the UK. Energy Policy (2012),

I found this paper via one of the many publications I scan via RSS. The paper has two slants to it – an excellent history of zero carbon and the route UK government have taken to date, and then a less persuasive, but comprehensive look at Passivhaus. I’m going to mostly look at the zero carbon aspects in this post and maybe return to the Passivhaus stuff (SAP vs PHPP etc) at a later date. If you’re fan of Passivhaus, it’s worth hunting out in the meantime.

The key aspect the paper explores is if the revised definition of ‘zero carbon’ dwellings in the UK and the approach to implementing this policy, advocated by the Zero Carbon Hub (ZCH), is coherent with overarching climate change and energy policies. Basically, is the zero carbon definition going far enough to contribute to the target of 80% reduction by 2050.

Of course, we still don’t have a final definition of zero carbon, although there were some heavy hints this week in the proposals for the future Queen Elizabeth Olympic Park. Within the sustainability commitments the targets for “ENERGY CONSERVATION & CARBON REDUCTION” for new construction is:

  • In addition, achieve Zero Carbon Homes requirement before the standards apply; require a 65% reduction in emissions over Building Regulations 2010 through fabric improvements and on-site features.
  • Permit up to 35% of emissions mitigation through allowable solutions in surrounding communities as part of the Development Corporation’s regeneration remit. Allowable solutions will be developed in collaboration with Boroughs and local partners.

So zero carbon could end up being a 65/35 split between on-site and allowable solutions, but we still don’t know.

The paper is very critical of allowable solutions:

…the introduction of allowable solutions has effectively introduced a buyout clause. Depending upon what level of Carbon Compliance is finally adopted, market based ‘allowable solutions’ could comprise the majority of the net carbon savings from a ‘zero carbon’ home.

Implementing a revised definition of ‘zero carbon’ that introduces the concept of carbon offsetting to the built environment raises a number of critical uncertainties. The choice of methodological approach, the definition of boundaries used in the reporting of emissions, and ultimately the efficacy of the chosen policy approach in responding to climate change must all be evaluated.

The concept of ‘allowable solutions’ is effectively a form of carbon offsetting. The economic rationale behind this approach is that emission reductions can be made at the least capital expenditure, thus maximising the short term economic benefit to industry (Kill et al., 2010). This type of indirect carbon reduction strategy has the fundamental weakness that it does not directly address the source of the problem and as such is vulnerable to the issues which affect carbon offset mechanisms in general.

As with most forms of carbon offsetting, the use of ‘allowable solutions’ contains two inherent vulnerabilities, (i) additionality and (ii) permanence

This may well be the case, but unless something very dramatic happens, it looks like we’re saddled with AS. For the definitive view on current thinking regards AS, check out ZCH paper Allowable Solutions for Tomorrow’s New Homes.

The greatest concern highlighted in the paper is that we appear to be pedalling backwards:

According to the ZCH Energy Efficiency task force report, the proposed standard ‘‘equates to around a 20–25% reduction in carbon dioxide emissions compared to current Part L 2006 compliance’’ (ZCH, 2009c). In other words, if the ZCH recommendations are implemented many of the nations’ future ‘Zero Carbon’ dwellings may perform little better than buildings currently being constructed to comply with the legal minimum standards permitted by Part L (2010) of the UK Building Regulations. The percentage growth in new households in the UK by 2050 is anticipated to be greater (Boardman, 2007 (pdf); DECC, 2010a) than the percentage savings achieved by the FEES energy efficiency standards. Accounting for stock expansion means that the net contribution of the new energy efficiency standards to national GHG abatement targets is likely to be negative. If the anticipated 50% growth in the rate of UK domestic hot water consumption and growth in cooling demand (DECC, 2010a) is also factored into this equation then it is highly unlikely that the FEES standards can make a contribution to the UK climate change abatement targets.

On the one hand, this worries me immensely. I’m going to have to do a little more research to corroborate the arguments here. On the other hand, the concern I have that 2013 and 2016 aren’t going far enough fast enough doesn’t seem to matter as much when set in this context.

The purpose of all this background was to construct an argument in support of Passivhaus, which I think the paper gets slightly backwards. I’d have been happier if they’d modelled what would make a meaningful contribution to carbon reduction and then proved that Passivhaus was one method to meet this, rather than starting from Passivhaus.

A thought which occured to me whilst reading this paper – when we finally agree upon the energy efficiency standards for 2016 (hopefully an improvement on the proposed 2013 8% plus FEES), will that be the end of incremental improvements for fabric energy efficiency to the Building Regs between 2016 and 2050? After all, technically we will be at zero (even though we won’t be) and logic dictates that you can’t have less than zero…

The paper expresses a concern that the current revised definition of zero carbon does not include unregulated and embodied emissions. It would make sense that any changes to Building Regs between 2016 and 2050 ought to start to take into account embodied energy.

I can see myself returning to this paper again and again in the future – highly recommended.