We all know that you can add value to your house by extending it wherever possible. Middle-class terraces in any given city are characterised nowadays by at least one property on the street flaunting a giant tarpaulin in the front garden – a sure sign of a basement conversion. Loft up-dos, meanwhile, are so run-of-the-mill, a dormer window is something of a cliché. Both basements and lofts, if turned into self-contained flats, mean extra cash to a would-be landlord.

But why confine yourself to the roof or basement? Why not convert the garage into a self-contained, rentable flat? I became intrigued by the notion when an architect mate of mine visited my parents’ beachside house in Cornwall, which has an enormous garage attached to the side.

“This double garage is amazing,” he enthused. And not because it contains a ping-pong table, either. “You could extend your whole property here. Build up another storey. Have another cottage.” Needless to say, my parents weren’t keen, but since then I have been rather sold on the idea of using dead space once intended to house a car for something more creative.

Gilly Carpenter is a landlady with a portfolio of eight houses in the home counties. One of them, a substantial three-bedroom home in Banbury, has a single garage attached, which, in the next two weeks, she is having converted into a studio flat.

Background

• Tales of a landlady: Tax reforms

• Into the sunset

Background

• Tales of a landlady: Degrees of success

• Tales of a landlady: It pays to shop around

• Tales of a landlady: Residents only

• The ties that bind

• How low can you go?

Background

• Tales of a landlady: Avoiding the agents

• Tales of a landlady: In the dock

• Tales of a landlady: the age of reason

• Tales of a landlady: Heroes and villains

• Tales of a landlady: High maintenance

Background

• Back to the ’burbs

• A waste of energy?

• Tenants like gardens, but not tending them

• In the doghouse

• Parking mad

It’s eviction time

Can investors profit from the rise in repossessions?

• It’s eviction time

Background

• Do property workshops work?

• A letting gamble

• Spread betting

• When buy-to-let turns from a hobby into a living

Tales of a landlady: Persistent complaint

How can lettings agents justify annual renewal fees, asks Rosie Millard

Background

• Landlords: halo or horns?

• Bidding wars

• Time to quit the ring?

“It’s only 5 metres by 2.5 metres by 3.3 metres at the highest point, but fortunately it backs onto a conservatory, so we will use that for living space,” Carpenter says. “I’m having a sink put in, with a kettle and a microwave. It will be perfect.” The work is a turnkey project that will cost £20,000 all in.

Outwardly, not a lot will change. The garage door will become the front door, and a window is being installed at the back. “I could have had one in the front, but I am sensitive about my neighbours, who were a bit worried I was building a house of multiple occupancy. I don’t think I will need planning permission, because I’m not changing the shape or size of the building,” Carpenter says.

Unfortunately, she is not quite right. “If the garage is your own, and you want to extend your own domestic accommodation within the structure of the existing garage, then generally speaking, you don’t need consent,” says the Sunday Times planning expert, Michael Haslam. “But if you want to create a self-contained unit to rent out, you will absolutely require planning consent, because you are creating an additional unit of accommodation. The council will need to see where your garage is, and if it is appropriate for this purpose. They may be perfectly happy, but you will require consent.”

All being well, this should be granted, although the process will probably take several months. If she does get the go-ahead, Carpenter might be looking at an attractive package: the studio flat and the original three-bedroom house could be let out separately, but together the complex might make an alluring option.

“What I would like to do is short-let the house to business people at, say, £1,300 a month,” she says. “Then I will rent out the studio flat for £400 a month, maybe more. If my tenants are Americans with a teenage child or a nanny who can go in the studio flat, that would be ideal. Tenants aren’t interested in gardens, but an extra living space usually goes down well.”

Is anyone else in her area doing the same thing? “Not in my street. But I suspect they’ll all want to.”

Phil Bateman is managing director of the Garage Conversion Company (garageconversion.com), whose team has been charging around the country doing this sort of work for the past five years; they have carried out more than 2,000 jobs. Although most of their clients are looking for an extra room, a significant minority (about one in five) asks them to transform the garage into a studio flat for nanny, granny – or tenant.

“The trickiest thing about converting a garage is to make sure it doesn’t look like a converted garage,” says Bateman. “You have to match brickwork and windows to the existing house.” He has an in-house architect, and an office to take care of the paperwork, such as planning consents. It ensures that conversions comply with building regulations, making sure that insulation, ventilation and foundations are all up to scratch.

The cost doesn’t sound bad, for what you get: “Putting in a kitchen and bathroom would cost about £20,000.” How long will it take? “A single garage conversion will take two weeks, and there is generally a four-week lead time.” Although, if you are making a separate living space, factor in the time it takes to apply for – and, you hope, get – planning permission.

But can you realistically make something designed to house just one car into a bijou residence? Yes – just, says Bateman. “At a squeeze, a single garage, which is usually 5 metres by 2.5 metres, could be a single flat.” Double-garage conversions sound more attractive: Bateman says that could give you a living area, open-plan kitchen, bathroom and bedroom.

It sounds a great wheeze. So, why bother hunting around for something that you can rent out, when it could just be in your garage all along?

buytolet@sunday-times.co.uk

Times recommends

• Analysis: frustration for everyone - except investors
• Buy-to-let: professional investors cash in on the credit crunch
• Ten things you need to know about house prices