One of the surest ways to add value to your home is to get creative with the space. Knocking down a wall — for instance, between a bathroom and loo to create a bigger bathroom — will usually increase value, especially if you have a separate lavatory elsewhere. However, for the ultimate money-spinner, try conjuring up extra space.

Turning a three-bedroom house into a four-bedroom house, for example, is usually achieved by extending at the back or to the side, for which you need to call in the professionals. Large one- and two-storey extensions require planning permission and can involve months of disruption and filth. You may have to move into rented accommodation — so get an architect, find a reliable builder and visit the bank manager.

However, it may be possible to convert existing unused areas into bonus space. In central London, the sums make stark reading. Converting a loft in Chelsea to what’s known in the trade as a “Chelsea finish” might cost £1,500 to £2,000 a square metre, but when you consider that property in the royal borough costs £7,000 to £10,000 for each and every square metre, it’s easy to see that it’s a job worth doing.

Outside London, too, it’s hard to go wrong by adding an extra room. Attics are good hunting grounds for unused floor space, though converting a loft into a full-sized room can create upheaval.

The floor will need to be strengthened, which can take up to 15cm off the height of the room. Ring your local council to check whether it stipulates minimum headroom requirements, but in any event it’s wise to aim for at least half the space to be 2.4m high. Raising the roof can give back a lot of wasted space in the corners but it can be hard to get planning permission to do this. Whatever you are designing, contact your local council to find out what permissions are necessary.

Velux skylights will provide extra light, but dormer windows — as wide as you can get away with — are even better as they’ll give you more space and add interest. You can probably ditch the water tank as they aren’t usually necessary these days.

The big problem with loft extensions is access. Granny won’t want to clamber up a ladder, and though most three-year-olds will be happy to, their parents couldn’t stand the stress. Planners don’t like them either.

If you install a full staircase, make sure you comply with regulations about the angle of the staircase, the width of the tread and the height of the rise. They do steal a lot of space from the floor below, however, so consider alternatives such as installing an external staircase and glazing it over. This could double as a fire escape, which you’ll need in any building with more than five storeys.

Attics are notoriously hot in summer and cold in winter, so it’s worth paying for the best insulation you can get — a couple of thousand pounds should suffice. Do the floor while you are at it, for soundproofing and fireproofing.

Building a loft extension is complicated and you could probably do with getting an architect and a structural engineer in to help deal with problems such as the weight of new walls.

Besides planning permission, you’ll need building-regulations approval and party-wall consents from any adjoining building. If your house is listed or in a conservation area, you may find extensions aren’t allowed at all. Regardless of where you live, you probably won’t be able to get permission to raise the roof higher than the neighbours’.

Even for a small conversion in a Victorian terrace or semi, you’re unlikely to get change from £30,000. Larger projects — such as adding two bathrooms and top-of-the- range fittings — could push the bill up to £80,000 and you could find you don’t make a profit. When you’ve finished, get a certificate from the council to prove you’ve done it all correctly or the house will be difficult to resell.

With a bit of imagination your conversion can become a real focal point in the house. The architect Gordana Mandic, for example, devised a sweeping spiral staircase — which cost about £4,000 — when she converted the loft in her London flat. A wooden, metal-clad post forms the central support for steps made of simple metal L-profiles attached to the walls and covered with double-width MDF and a top layer of oak. “With a good carpenter it’s simple,” she says. “Any metal worker will make the L-profiles, though you’ll need precise drawings.”

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