In a bid to avoid the hassle and cost of moving, 90% of homeowners have renovated their property over the last five years, with 58% carrying out extension work such as loft conversions, new garages or extra bathrooms, according to new research by uSwitch.com.

However, 30% of consumers have insurance policies at risk of being invalid because they have failed to notify their home insurer about the work they have carried out.

With 12% of homeowners forced to scale-up their property as they can’t afford to move, many are shelling out an average of £15,000 sprucing up their homes. But most buildings insurance policies are based on the structure of the house as it stands when the policy is taken out – so adding a new room or knocking through a load-bearing wall could significantly affect the terms of the cover.

Many policies could become invalid when the house is significantly altered, such as after an extension, a loft or garage conversion or even adding a new bathroom. Despite this, only 17% of homeowners check their insurance policy and contact their provider before work begins.

The research also reveals that consumers are failing to adequately protect their homes when the work is actually being carried out. 43% did not take steps to arrange extra cover for accidental damage to possessions or the increased security risk of open walls or removing doors and windows.

In addition, 49% of home improvers failed to check whether their tradesman was certified, leaving themselves open to being short-changed. And 71% prefer to pay contractors in cash whenever possible – but with no paper trail, homeowners will be left exposed if the job is not completed as promised.

Michael Ossei, personal finance spokesperson at uSwitch.com, said: “We are a nation gripped by extension fever, with many people deciding to create more space in their existing home rather than move. But, with all the emotional and financial challenges of building work, home insurance is often the last thing on your mind. It’s absolutely vital to get in touch with your insurer before you start on any home improvement project to see how it will affect your policy.

“If you are extending your home you are likely to be increasing the rebuild cost – so you will need to make sure this is updated with your insurer. You might need to buy specialist insurance if your home has been built in an unusual way – such as if it has timber frames or another non-standard feature. Plus, if any external windows, doors or walls are removed during building work, you will be more vulnerable to burglaries, so you also need to make sure you are covered for this.

“It is also important to make sure the builders have public liability insurance to cover any accidental damage that happens during the work. With almost half of homeowners borrowing money in order to fund their building projects, the last thing you want is to get into extra debt if something goes wrong.”