The average new home in the UK costs its owner £1,000 more a year to heat than it should, a direct result of building standards that exist on paper but not in practice. That figure, from an analysis by the Building Performance Network, lands at a time when the energy price cap sits at £1,928 for a typical household and the government is pushing heat pumps as the future of home heating.
As reported by The Guardian, the analysis compared design-stage energy performance certificates (EPCs) with actual energy use in over 200 new homes. The gap was consistent across all house types: flats, terraces, and detached houses all underperformed by 50 to 100 percent. A home built to use 6,000 kWh a year might burn through 12,000 kWh in reality.
Why the performance gap exists
The root cause is not the regulations themselves, Part L of the Building Regulations sets reasonable targets for fabric efficiency and ventilation. The problem is enforcement. Builders routinely install cheaper insulation, leave gaps in the thermal envelope, and fail to seal service penetrations. Air tightness tests, meant to catch these defects, are often passed on the third or fourth try after temporary fixes that degrade within months.
For a buyer, the consequence is a home that feels draughty, costs more to heat, and may fail to reach its advertised EPC rating. That matters because EPC ratings affect mortgage eligibility and green finance deals. A home rated C on paper but E in practice could cost an extra £200 a month on a standard variable tariff, according to Ofgem’s typical usage figures.
But the worst part is that the buyer has no easy recourse. New homes come with a warranty, typically the NHBC’s 10-year cover, but it rarely covers energy performance. The builder is not liable for the gap between design and reality unless the home is uninhabitable.
What it costs a typical 3-bed semi
Take a typical new-build three-bedroom semi-detached house. The design EPC might show a C rating with annual heating costs of £900. In reality, poor insulation and air leakage push actual consumption to 14,000 kWh of gas per year, plus 3,000 kWh of electricity. At current price cap rates, 6.24p per kWh for gas and 24.5p for electricity, the real bill comes to roughly £1,740. That is £840 more than the design estimate, and £1,000 more if you include standing charges.
The analysis from the Building Performance Network found that the average gap across all new homes was £1,000 per year. For a household already stretching to afford a new-build mortgage, that extra cost is the difference between a comfortable home and one that leaves rooms unheated in winter.
How to fix a new build that underperforms
The catch is that new-build buyers are not stuck forever. Retrofitting is possible, though it costs money and disrupts daily life. The most effective first step is a professional air tightness test and thermal imaging survey. These cost between £200 and £400 and will pinpoint exactly where heat is escaping, usually around windows, doors, loft hatches, and pipe penetrations.
Sealing those gaps with mastic or expanding foam is cheap, typically £100 to £300 for a whole house. Adding loft insulation to the recommended 270 mm depth costs about £400 for a DIY job on a 3-bed semi. If the cavity walls are uninsulated, which should not happen in a new build but does, blown-in insulation costs around £700.
For homeowners willing to go further, a heat pump can replace a gas boiler and slash running costs by 30 to 50 percent, especially if paired with better insulation. The Boiler Upgrade Scheme offers a £7,500 grant towards an air source heat pump, and the Great British Insulation Scheme provides free or subsidised insulation for low-income households. The Energy Saving Trust estimates that a heat pump in a well-insulated new build can cut annual heating bills to under £600.
But the real fix is regulatory. The government’s Future Homes Standard, due in 2025, will require new homes to produce 75 to 80 percent less carbon than current standards. That will mandate better fabric efficiency, heat pumps as default, and tougher enforcement. Until then, buyers must treat EPC ratings with deep scepticism and budget for post-completion upgrades.
What to do now: if you own a new build that feels cold or costs more than expected, book a thermal imaging survey. Apply for the Great British Insulation Scheme through gov.uk. And contact your MP to demand that the Future Homes Standard includes mandatory post-completion performance testing, not just design-stage modelling.
Frequently Asked Questions
Probably not. The warranty covers structural defects, not energy performance. Unless the home is uninhabitable, you have little legal recourse. Your best bet is to retrofit insulation and air sealing yourself, then claim under the Great British Insulation Scheme if eligible.
It should, if enforced. The standard will require new homes to have heat pumps, better insulation, and lower carbon emissions. But enforcement is the weak link, the government must introduce mandatory post-completion testing to ensure homes perform as designed. Without that, the gap will persist.
