Retired midwife Margaret Biddle and her husband, John Hughes, went a lot further than this, using savings and money borrowed from family to retrofit their 1970s bungalow near the north Wales coast. 

The works, designed by Paul Testa, of Sheffield-based Paul Testa Architecture, included adding external wall insulation for £16,000, fitting triple-glazed windows and doors (£20,000), adding solar panels (£12,000), putting in underfloor heating (£10,000 plus installation costs) and replacing the oil boiler with an air source heat pump (£9,000).

“John’s been a vicar for 20 years and we’ve lived in several draughty rectories with high ceilings which were very expensive to heat, very wasteful of energy, and I was still cold,” Ms Biddle said. 

The couple wanted to be as environmentally responsible as possible and reduce their energy bills, which have halved to £1,200 a year. “We’re in a climate emergency but I also wanted the bungalow to be cosy,” Ms Biddle said.

A deep retrofit of an existing home is not cheap – Mr Testa would expect about £1,200 per square metre (including VAT) to bring a property to EnerPHit standards, the Passivhaus certification for retrofits.

“While it does depend on where you live, it’s unlikely your house will be worth what you’ve spent on it, and the payback in bills is not short-term, either,” he said. 

“However, I have retrofitted my house, and my family and I now have a beautifully comfortable home, with excellent air quality and low running costs. That feels like an excellent investment.”

This article is kept updated with the latest information.