Homes given poor energy ratings on the basis of faulty modelling

Homes could be given poor energy efficiency ratings on the basis of flawed modelling, a new study has suggested.

Houses in the lowest bands G and F were found to use 48 per cent less energy in the real world than estimated by the modelling used to rate them, University College London found.

The findings point to several flaws in the energy performance certificate (EPC) system, which the Government has said it will rely on to force landlords to make net zero improvements to their properties.

The Government has proposed that landlords will have to get their properties to at least EPC C by 2028.

If they fail to get their ratings to the proposed level, landlords could face fines of up to £30,000.

However, most homes even in lower bands have been found to already be running at EPC C levels in real-world conditions.

An EPC rating, which is required whenever a property is sold or rented out, is given by an external assessor, based on an estimated cost of energy.

Homes assumed to be the most expensive to run are given a G rating, and the least expensive an A rating.

Flawed assumptions

But experts say the modelling uses flawed assumptions, including that heat loss is based simply on the age of a building, and ignores factors such as the local weather conditions.

Cheap and easy improvements that can make a major difference to energy efficiency levels in a home, such as putting carpets down, do not count towards an EPC rating, the study noted.

There are also concerns that different inspectors may give different findings to identical properties.

“We found that homes in EPC bands C-G on average use significantly less energy than modelled by the EPC,” said Jessica Few, who led the UCL study.

“It isn’t yet clear what is causing the discrepancy, but there could be some technical issues in the underlying model, in the assumptions about key building characteristics, and some EPCs could be out of date because they are not automatically updated following an energy efficiency refurbishment.”

Michael Gove, the Housing Secretary, is understood to be concerned that flaws in the system could undermine the rental and housing market because of the cost of getting to a higher rating.

Mr Gove is reportedly considering pushing back the date or lowering the rating requirement.

There are also concerns that the EPC system could be holding back improvements needed to get to net zero, in particular installing heat pumps, because of the cost of electricity.

Jan Rosenow, an energy expert at the Regulatory Assistance Project, saw his EPC certificate drop from a D to an E even after installing a costly air source heat pump system.

“The EPC software overestimates the energy use from the heat pump by a very large margin in my case, so massively overpredicted how much it would use,” he said.

Despite having better insulation, including triple glazing, wall insulation and floor insulation, his home in Oxford was given a lower rating than his next-door neighbour.

“The assessor couldn't verify whether the wall was really insulated. But how do you validate it? You can't open up the wall.”