Homeowners sitting on an unused attic could be missing out on a property goldmine – with a loft conversion potentially adding more than £65,000 to the value. new figures reveal.

Research by Nationwide found that adding a loft extension with a bedroom and bathroom can boost the value of a typical three-bedroom, one-bathroom home by as much as 24%. That’s equivalent to an extra £65,279 on a property worth £271,995.

By comparison, adding a single extra bedroom raises the price by around 13%, or £35,000, while extra floor space or another bathroom adds £13,600 and £10,880 respectively.

Nationwide’s senior economist Andrew Harvey said: “Home improvements that increase the size of the property, such as an extension or loft conversion, remain a compelling way to add value.

“A loft conversion or extension incorporating a large double bedroom and bathroom can add as much as 24% to the value of a three-bedroom, one-bathroom house.”

The lender’s analysis shows the biggest percentage gains come from turning a two-bedroom detached home into three bedrooms – adding up to 17% – while converting a three-bed terrace into a four-bed boosts value by about 10%.

However, Nationwide cautioned that homeowners should ask themselves whether they really need the extra space. More than half of owner-occupied homes in England are “under-occupied”, meaning they already have at least two spare bedrooms.

Mr Harvey added: “Many households buy properties they intend to grow into over time, as their families expand. But increasingly, spare rooms are being used as home offices due to hybrid working.”

How much value an extra bedroom can add

Property type – 2-bed to 3-bed – 3-bed to 4-bed

Terraced – +13% – +10%

Semi-detached – +14% – +10%

Detached – +17% – +13%

Kitchens and bathrooms still most popular

While loft conversions add the most value, kitchen and bathroom renovations remain the most common home upgrades.

Nationwide found 71% of homeowners who had carried out improvements in the past five years focused on these rooms.

More than two in five (42%) added a bathroom or ensuite, while a quarter installed an extra toilet.

Mary-Lou Press, of the estate agents’ body Propertymark, said: “While new kitchens and bathrooms have long been known to enhance property prices, clever home improvements such as loft conversions give houses vast new space and typically help add substantial value down the line.”

Even so, only 24% of renovators opted for a loft conversion, compared with 39% who built an outbuilding such as a garden room, and 23% who added a conservatory.

The main motivation for doing up a property wasn’t to make money – just 35% said they were looking to boost value. The majority simply wanted to improve the appearance of their home.

Eco upgrades on the rise

Nationwide also found a growing appetite for “green” improvements, with a third of homeowners (34%) making eco-friendly upgrades such as solar panels and insulation.

More than half of these added solar panels, while others installed cavity wall insulation, air source heat pumps or electric vehicle charging points.

Mr Harvey said the trend reflects rising energy costs and the need to cut emissions from Britain’s housing stock – which accounts for about 15% of the UK’s greenhouse gas output.

“Over the past decade, energy efficiency has improved significantly, with more than half of UK homes now rated C or above for energy performance – up from less than a quarter in 2013,” he said.

Check before you convert

Experts warned that those planning a loft conversion must ensure they comply with planning rules.

Ms Press said: “Most loft conversions fall under permitted development rights if they stay within strict limits, but some require full planning permission. Homeowners must also check if their property is listed or in a conservation area before making alterations.”

Despite the expense and upheaval of renovation, only 4% of those surveyed regretted the work – most commonly because of cost overruns or disappointment with the results.

For the rest, the investment appears to have paid off handsomely – particularly for those who decided to take their home’s value to new heights by converting the loft.