Satellite data and computer vision could unlock cheaper retrofits

Two-thirds of UK homes still have an EPC rating of D or below. That is roughly 19 million properties leaking heat and money. The standard route to fixing them, a retrofit assessment, costs £200 to £600 per home and requires a surveyor to visit, measure, and photograph every room. It is slow, expensive, and puts off precisely the households who need help most.

New work from the Stockholm Environment Institute, published this month, suggests a faster way. Researchers used publicly available data, Energy Performance Certificate records, Ordnance Survey maps, and aerial photographs, combined with a computer vision model trained to spot insulation defects. They tested it on 700 social housing blocks in London. The model identified which buildings had cavity-wall insulation, which had solid walls, and which had missing or damaged insulation. Accuracy was over 85% for most categories.

Who qualifies, and who doesn’t

The study focused on social housing, but the method works for any home visible from above. Semi-detached houses, bungalows, and terraced rows all appear in aerial imagery. For flats in high-rise blocks, the model can assess the roof and top-floor walls. The catch is that it cannot see inside. Internal insulation, loft hatches, and underfloor upgrades are invisible from the air. So the technique is best used as a triage tool: flag the homes that almost certainly need work, then send surveyors only to the ambiguous cases.

Ofgem and the Department for Energy Security and Net Zero have not yet adopted this approach. But the Energy Saving Trust told the Axiom team that “any tool that reduces assessment costs is welcome, provided it meets the accuracy standards for PAS 2035”, the government’s retrofit quality framework. The study’s authors estimate that scaling this method across England could cut the national survey bill by £140m a year.

What it costs a typical 3-bed semi

For a homeowner in a 1930s semi in Manchester, a full retrofit assessment today runs about £350. If that could be replaced by a £50 automated desktop analysis, or bundled free with a local authority scheme, the saving is £300. That is the difference between proceeding with a heat pump quote and abandoning it. The average air-source heat pump installation now costs £7,000 to £13,000 after the Boiler Upgrade Scheme grant. Reducing the upfront friction by even a few hundred pounds matters when household budgets are stretched.

The study also found that the computer vision model could detect solar-panel-ready roofs: orientation, pitch, and shading from nearby trees. That data is already available from satellite imagery, but it is not yet linked to EPC databases in any systematic way. A single platform that shows you your roof’s potential, your wall type, and your likely grant eligibility, all generated from public data, would be a genuinely useful tool.

The catch: data gaps and privacy

What this misses is the human element. Aerial images cannot tell you whether the loft has been boarded, whether the cavity walls have partial fill, or whether the tenant has mould. The researchers acknowledge that their method works best on uniform housing stock, estates built in a single phase with consistent materials. For Victorian terraces and mixed-era conversions, accuracy drops. And while the data is public, some residents may object to their home being scanned without consent. The Information Commissioner’s Office has not yet ruled on whether this use of aerial imagery falls under the UK GDPR exemptions for public-interest research.

But the direction of travel is clear. The government’s own Net Zero Strategy calls for 19 million homes to be retrofitted by 2050. At the current rate of 60,000 upgrades per year, that target is unachievable without a step change in assessment speed. Computer vision will not replace the surveyor. It could, however, replace the clipboard.

Households in social housing can ask their landlord whether they are using any automated assessment tools. For private homeowners, the best first step remains the Energy Saving Trust’s home energy check at est.org.uk. If the London trial expands to a national rollout, eligibility for free or subsidised assessments could open as early as 2026.