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How to prepare a Net Zero Strategy for your housing stock

For over a decade our clients have used SAP scores to drive their energy efficiency strategies.

This has been bolstered by the introduction of SAP-based Minimum Energy Efficiency Standards in the private rental sector and indicative standards for others.

But a new target is in town, and the SAP Rating is not the right tool to target Net Zero.

SAP 100 ≠ Net Zero

The SAP Rating is a fuel-cost-based energy efficiency rating, and as such, ‘better’ scores can be achieved (in an otherwise identical house) by more polluting fuels where they are cheaper than renewably-sourced heat or power.  This means that, for now, gas central heating is still being put into old homes despite the policy intention to ban it from new ones.

This trap is exacerbated by basing calculations on historic measures of carbon emissions. As more electricity generation is generated from renewable sources, grid-powered heat pumps are able to compete with, and then beat, highly efficient gas central heating on their carbon emissions.

Net Zero requires we identify every potential saving, and there are few opportunities to make major changes in housing, so there is a risk that opportunities are lost whilst the SAP Rating dominates decision-making.

The decarbonisation of the Grid

Emissions in the power sector fell by 46% to 43 MtCO2e in 2017 alone, with a predicted (pre Covid-19)  fall to 31 MtCO2e by 2020 and on to 6 MtCO2e by 2035, driven by a range of industry and small-scale policies:

  • Large Combustion Plant Directive 
  • Industrial Emissions Directive 
  • EUETS 
  • UK Carbon Price Support 
  • Feed-in-Tariffs (for small scale generation) 
  • Renewables Obligation and Contracts for Difference (for large-scale generation) 
Figure 1: Emissions Intensity (all power producers), Source: BEIS, 2019

We have mapped these reductions, and on to 2050, into our CROHM analytics service so that clients can consider the impact of their retrofit plans against the different carbon scenarios.

Scenario testing in a decarbonising system

Clearly the more your stock is reliant on electricity, and the more the Grid decarbonises, the less work you may think you need to do to housing. But with the country also set to decarbonise transport and industry, the Grid cannot meet the needs of every home and keep bills affordable if we do not reduce demand at the same time as reducing supply.

For this reason, whilst we provide later scenarios, our recommendation is to model scenarios to the mid 2030s. At this point, in the RdSAP method, carbon emissions will have fallen sufficiently to show the benefit of switching to electrified heating, but efficiency through efficient heating systems and demand reduction is also rewarded. 

But what about bills?

We hear you. Net Zero comes with a running cost whilst fossil fuels have the price advantage: at current prices our models show a ‘Net Zero’ housing stock could deliver an average SAP as low as 75 . 

There is no point decarbonising heat if people can’t afford to run it – causing stress elsewhere in our society, most notably on the NHS through cold-related illnesses. Sustainability comes from hitting environmental, social and economic targets simultaneously. 

Our scenario testing uses a layered approach so it can consider these multiple goals. And this is the way you develop a strategy: incorporating your objectives, any restrictions, your business-as-usual impacts, and then delve into how you handle the remaining uncertainties, challenges and opportunities.

  1. Set targets in SAP, carbon, kwh, kwh/m2 and/or bills.
  2. Layer in business-as-usual improvements: planned works, grid decarbonisation and regulation.
  3. Layer in financial factors: cost of interventions, funding opportunities, and budgets per home or by programme
  4. And we’ll model over 2400 measures to test what you can do, for every address, in budget, to work towards your target.

Our approach means that a strategy can take into account short-term goals to eliminate risks of Excess Cold (SAP F&G), or improve homes at risk of fuel poverty to EPC Band C, but those interventions can be planned in a way that contributes to the overall target of Net Zero without duplication of effort or cost. 

And our data analytics means that scenario testing can be processed at address level for thousands of homes, producing not only a whole-stock strategy but also whole house plans for each home in order to deliver it.

What are housing associations doing to deliver Net Zero?

By their nature, our clients tend to be pioneers in decarbonisation, and so their actions today are the direction of the sector for tomorrow. By taking up our CROHM service, they all have whole house plans for all their properties, but there are four lessons we’d particularly highlight from their experience: 

  1. A 2050 Net Zero target is not a long-term target when you have thousands of homes to improve, and face the risk that the timetable could be accelerated as the climate crisis worsens.
  2. Voids are not a cost, they are an opportunity to bring a home up to your Net Zero standard – but you need to have a plan ready.
  3. Our clients are curious about new technologies but are not waiting for them. They understand what they can do to their homes now, and know they can only manage what they can control.
  4. More and more are moving away from gas central heating – they know they need to spread the cost of decarbonising homes, and to take the opportunities as they appear.

Is SAP relevant in a Net Zero world?


SAP is not just a rainbow coloured Rating.

The SAP Rating is just one output from the Standard Assessment Procedure, along with thousands of trained surveyors, a regulatory regime that enables invaluable data collection on the housing stock, and millions of data points that tell us not only what the current energy performance of a home is, but also – in the right hands (ours, of course!) – what it could be and how to get there, at least cost. 

Please contact us if you want further help in developing a roadmap to get your housing stock to Net Zero.