Experts analysing 21 million homes across England and Wales found 58 per cent only meet insulation standards of 1976 or earlier.
As a result, they lose more heat through wall cavity insulation, double glazing, loft insulation and floor insulation than modern regulations insist on today.
Around 1.6 million properties (7.5 per cent), have an insulation age of 2002 or younger, and 4,663 have an insulation age of 2013.
But the average semi-detached homeowner could save up to £285 a year if they upgraded their cavity-wall insulation, and a further £255 by having a well-insulated loft.
Energy bills for these residents could also be reduced by an additional £390 a year if they updated their solid-wall insulation.
The study, conducted by EDF in partnership with property data platform, Sprift, analysed the current levels of home insulation, including floor, roof, window and wall, against building regulations of homes across different time periods to calculate the nation’s ‘home insulation age’.
It comes after additional research of 2,000 homeowners, commissioned by EDF, found just 37 per cent have ever updated their property’s insulation.
A quarter (25 per cent) haven’t done so because it’s too expensive, while 19 per cent would rather spend money on other things.
And 17 per cent don’t know what type of insulation they’d need in the first place.
Philippe Commaret, Managing Director for Customers at EDF, which has announced they will spend an extra £20 million on energy efficiency measures for fuel poor households this year, said: “It’s surprising the average insulation age of a home is over 40 years old, with so few homes having sufficient insulation installed to meet modern energy efficiency standards.”
Jade Lewis, Chief Executive of the Sustainable Energy Association said: “Energy Efficiency measures are essential foundations in our nation’s transition to Net Zero, for too long many UK homes have remained poorly insulated and heated.
“These inefficient buildings are impacting not only our progress to Net-Zero, but also our energy security, our nation’s health, and wellbeing, and are contributing to fuel poverty, which will only increase as we weather the storm of our current energy crisis.
“The SEA believes now is the time to invest in making our buildings healthier, reducing greenhouse gas emissions, and lowering their running costs and we will continue to support the initiatives, like EDF’s, which will make this a reality.”
The study also found 21 per cent of homeowners have no idea about the different ways properties can be insulated to improve their energy efficiency.
However, 65 per cent of those who have thought about, or updated, their home’s insulation recognise it helps save money on energy bills.
The research, conducted via Onepoll, also found two thirds didn’t know the EPC rating of their current property.
But 43 per cent have made changes or considered making updates to their home energy efficiency for the good of the planet.
Philippe Commaret added: “As energy prices continue to rise, quality insulation is the most effective way to cut household bills permanently, however this is often overlooked as the cost of installation is a significant barrier to many.
“That’s why it’s so important that we work with Government and industry to find new ways to get more homes insulated as soon as possible and why we’ll be supporting our vulnerable customers to help insulate their homes now, ahead of bills rising again in October.”