Energy savings from insulation ‘vanish’ after four years, study claims

The surprise findings, published by Cambridge researchers, suggests that while insulation has ‘very real benefits’, it is not a ‘silver bullet’ in the fight to make homes more energy-efficient.

It comes as a key parliamentary committee said that by 2025 one million homes a year should have insulation and other energy efficiency measures installed to help cut energy use.

But the report, based on research which looked at 55,000 homes over 12 years, suggests that the benefits from cavity wall insulation are offset after four years on average, possibly by a ‘rebound effect’ of people using more gas after the retrofit.

The exact reason why people use more gas after installing insulation is unclear, but researchers said it could be from turning up the heating, opening windows in stuffy rooms, or combining the retrofit with building an extension or glazed conservatory, which take up more energy.

Loft insulation has even shorter-lived benefits than in cavity walls, researchers claimed, only giving energy savings for the first two years on average.

Cristina Penasco, a co-author of the report, said: ‘We found that energy efficiency retrofits are often combined with home improvements that actually increase consumption, such as extensions.’

‘The recent spotlight on increasing the energy efficiency in UK buildings is both welcome and long overdue, and there are very real benefits to households from good insulation, not least in terms of health and comfort,’ the report’s co-author, Laura Diaz Anadon, added.

Diaz Anadon, who is the director of the Cambridge Centre for Environment, Energy and Natural Resource Governance, added that insulation should be combined with installing heat pumps and public information campaigns to encourage people to reduce their energy use.

The report comes as the the House of Commons Environmental Audit Committee (EAC) said earlier this month that all UK homes should have an Energy Performance Certificate rating of C or above by 2035, with insulation a key part of achieving this.

In a report on 5 January, the EAC wrote: ‘A national war effort on energy saving and efficiency is required.

‘Upgrading homes to Energy Performance Certificate C or above must be treated as a national priority to enhance the UK’s energy security, reduce bills and cut emissions from the country’s leaky and draughty building stock.’

RIBA president Simon Allford said in response that upgrading homes’ energy efficiency should be a national priority – ‘one we have long been calling for as a national retrofit strategy’.

Read the full report here.