If your home has a cellar – as many in towns and cities do – you’re probably using it as storage, but it could be much more useful – and valuable – as living space.

When you’re starting to outgrow your home, a cellar conversion can be a great way to make it bigger, without having to go to the hassle and expense of moving.

There are a couple of obvious problems with cellar conversions – lack of light and head height. These can be improved, but cellars are never going to be the lightest, tallest spaces.

For this reason, cellar conversions tend to make better bedrooms, bathrooms and playrooms than living rooms and kitchens, because the latter work best when they’re light and bright.

Few cellars have enough head height as they are, as the ceiling should be at least 2.4m (8ft) from the floor. This usually means digging down below the existing floor level and removing a lot of earth – an expensive and laborious task that can reveal hidden problems.

Converting a cellar is difficult if the house’s foundations prove to be shallow. If this is the case with yours, you’ll have to get the house underpinned, which isn’t cheap, although some cellar-conversion companies do this as a matter of course.

There may also be pipes in the way, but these can usually be moved. Rather than digging down, you may find it easier to have the floors raised in the rooms above the cellar, providing the ceilings in those rooms are high enough.

Another problem with cellar conversions is making them watertight, so it’s really important to get a reputable company or companies to do the work.

You can either employ an architect to draw up plans for the conversion (in consultation with a structural engineer) and a builder to do the work, or you can get a cellar-conversion company to do everything.

If you do use a builder, it’s a good idea to use a specialist damp-proofing company, too, because you don’t want to risk the conversion springing a leak.

Planning permission is usually required for cellar conversions – ask your local council’s planning department about this – not least because they usually involve a light well being dug in the front garden. Your architect or cellar-conversion company should be able to help you apply for planning.

Like all major building projects, conversions must comply with building regulations. The council’s building control department will want to check on the work as it progresses to ensure it complies and will have to sign it off at the end to make it legal.

You may also require permission from the freeholder (if you live in a leasehold property), and from your neighbours (if the cellar conversion involves a wall or boundary you share with them) so that you comply with the Party Wall Act.

A cellar below your home’s footprint will take around 12 to 24 weeks to convert, plus a few months for the planning stages. The cost should be from around £3,300 per sqm, depending on what’s involved.

Product of the week

The Bosch Prio sander, £50.98, B&Q, is a rarity because it’s cordless.

The Prio has a rechargeable lithium-ion battery and, unlike a lot of sanders, is light and manoeuvrable.

It also has a rubberised, ergonomically designed top, so it’s a pleasure to use, even for long periods.

A handy indicator light shows you when the battery is running low and when it’s fully charged. It charges in no time, and the charger doubles as a holder for sanding sheets.

You don’t even have to change the battery – just slot the Prio into the charger and plug the charger into the wall. A brilliant little sander.

How-to tip

The easiest way to paint around light sockets and switches is to undo the screws fixing the front plate to the box buried in the wall, then ease the plate away from the wall slightly (turn off the switch/socket and don’t touch the wires inside), so you can paint right up to the box without getting paint on the plate. Screw the plate back on when the final coat of paint is dry.