Achieving net zero homes | Sero discusses the challenges around decarbonisation

Achieving net zero homes | Sero discusses the challenges around decarbonisation

How do we make UK housing Net Zero? Andy Sutton, Co Founder and Director of Design & Innovation at Sero, outlines the challenge facing politicians, councils, RSLs, policy makers and contractors and suppliers to retrofit our housing stock to deliver genuine decarbonisation.

Our homes need to change. The UK’s homes and the activities within them generate about 40% of total national emissions. What’s more, the UK’s Climate Change Act 2008 (extended in 2017) makes the requirement to decarbonise a legal obligation, as well as a moral and ethical imperative: “Net Zero” is the law.

New home construction rates rarely break 200,000 in any year, so decarbonising the existing 29m homes in the UK is the priority — and it is a retrofit problem. But there are other issues — poor tools and understanding, few financial drivers, poor competency and quality plus the challenge of decarbonising the embodied carbon in the materials and retrofit process. In the next few articles we’ll unpick these, but we’ll start with the tools assessing what Net Zero actually is.

No legal definition
Despite legislation, the UK does not have a statutory definition of Net Zero. No precise legal definition means no proper
understanding and no agreed tools or method for measuring what’s net zero carbon — it unfortunately also means free reign for many claims of “green” and “zero carbon”. The prevailing definition is by the UK Green Building Council (UKGBC), which recognises that all carbon emissions from energy usage and occupancy of a home should be considered as part that home’s carbon footprint.

This is not in line with existing UK regulatory tools and certification schemes. The most important of these is the Building Regulation’s ‘Standard Assessment Procedure’ (SAP), and for retrofit the little sibling RdSAP (reduced data…). These are the statutory mechanism used to confirm the energy performance of buildings are above a notional minimum level. Every home in the UK must have a SAP score and consequential Energy Performance Certificate (EPC) — but it’s the wrong tool for assessing Net Zero.

SAP uses an energy metric to assess space heating demands and hot water needs, converting to carbon only as a yearly output based on an historic average annual carbon factor. But it is blind to the ongoing decarbonising of the national
energy grid and ignores the differences in the carbon emitted depending on when electricity is used.

SAP’s normalisations of climate and occupancy, which are right for assessing legislative compliance with a minimum
performance level, are for the same reason wrong for forecasting any individual cases. This is why the advice on the back of EPCs is so famously bad — it’s the retrofit equivalent of averaging complex dietary and nutritional advice down to “an apple a day keeps the doctor away”.

SAP ignores the unregulated energy use that’s plugged in by the occupants, which is around a third of the energy used in a
modern home. UKGBC’s definition of Net Zero, and our planet’s atmosphere, doesn’t exclude the impact of unregulated energy.

Carbon savings
Using the wrong tool for the job leads to poor outcomes. It means that photovoltaics dumping generation on the grid when it doesn’t need it will score you SAP points, but batteries that help to balance the grid gets you nothing. It means that athletic, jumper-wearing couples are told to spend thousands on insulation that will actually save them grammes of carbon (and pennies), not on a large hot water tank heating overnight that could save them kilogrammes (and pounds). And it means that manufacturers chase points not carbon — products claim to ‘achieve 2 SAP points’ but rarely do these deliver genuine carbon savings.

This isn’t to say SAP and rdSAP are bad tools, they are in fact very good ones for what they were designed to do. But you don’t put a screw in with a hammer: SAP might nail minimum energy compliance, but we’re all screwed if we use it to try and deliver Net Zero.

Header image ©by-studio/AdobeStock 

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