Basement conversions – expert ideas for planning the perfect basement conversion

A basement conversion can offer a whole extra floor of space within your home’s existing footprint and is perfectly placed for a generous kitchen-diner that opens out onto the garden.

If you love entertaining at home and want a spacious kitchen-dining-living area to suit all the family, but don’t have enough space on the ground floor, a cleverly designed basement conversion or lower ground floor extension might be just the way to create what you want.

It can be an entire floor of living space devoted to the way you like to cook, relax and enjoy a meal with friends, or simply catch up with the newspaper and a cup of coffee. And, open it up to the garden with floor-to-ceiling glass doors, and the space becomes filled with natural light and summer breeze on warm days.

See ourWhere to buy basements – to expand your living space

Basement conversions

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How much does a basement conversion cost?

Marc Stchedroff of Oxford & London Building Consultancy offers a guide cost of about £2,200 to £2,500 per sq. m. for the structural work, underpinning, excavation, steel work and screed, but not including fit out and decoration. Be aware that you will likely need to dig down further than the standard room height of about 2.7m, (to about 3.5m to accommodate underpinning and structural work) so it makes very little difference to the cost if you have an existing cellar already. And it can be more disruptive and controversial than other work on a house, such as a kitchen extension or loft conversion, because it may take longer, involve moving large amounts of subsoil for disposal and include underpinning a party wall. 'But the reason for digging out a basement is to create a spectacular space – a whole floor, if you want it,' says Stchedroff.

Do you need planning permission to convert a basement?

The planning regime covering the creation of living space in basements is currently under review, but do be aware that excavating to create a new basement which involves major works and alters the external appearance of the house, such as adding a light well, is likely to require planning permission. Building regulations also apply, covering areas such as fire escape routes, ventilation, ceiling height, damp proofing, electrical wiring and water supplies. Consult the government’s planning portal for advice, . You can also find out more at The Basement Information Centre,, which is a national centre for information about the development and use of basements, and also offers an online database of contractors.

Basement room

(Image credit: Jonathan Gooch)

How low can you go?

With space at a premium, especially in prime city areas, it may make sense to dig down to build a basement or convert a cellar to create the extra space that you need. It can be a viable alternative to the expense and hassle of moving, and a useful option if extending upwards and outwards aren’t do- able. 'A basement conversion can command the same square footage price as other floors in a property, as an average, and they have become far more accepted over the last few years thanks to modern engineering and design,' says Michael Wilson, director and head of sales for London-based estate agents, Mountgrange Heritage.

How long does a basement conversion take?

Generally, a conversion takes from 12 to 16 weeks for a structural shell on a small project, to 24 to 30 weeks for a bigger renovation, and up to a year for very large conversions.

Basement room

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Much of Britain’s Georgian and Victorian housing stock was built with a lower ground floor. Not only did such houses gain elevation and a more imposing façade by having the main entrance at a half or full level above ground with steps leading up to the front door, the lower ground floor could be used to accommodate domestic staff, provide sculleries, kitchens and storage areas. Now these lower ground floors can make ideal modern kitchen spaces, especially if you can enlarge the windows or replace them with glass doors to the garden, or extend them with a largely glazed structure to boost the sense of space and natural light.

'The goal is to maximise ventilation, natural light and sense of connection with the outdoors,' advises James Burrell of Burrell Architects. 'You may be able to cut back the floor above to introduce light, cut a light well all the way through the house, install a glass ceiling to borrow light from windows above – a good architect should be able to suggest all sorts of possibilities to allow you to make the most of your space.'

Basement conversions


The most successful basement conversions depend on a strong sense of space and light. Try to make your basement blend in with the existing structure so that it looks as though it’s always been part of the building. Consider blending the ground floor with the basement, perhaps via a glass balcony overlooking the new floor, which will help to integrate it into the property.

Light is essential, so opt for light wells where possible, allowing for the most generous sized windows that you can afford, even if this means sacrificing some space at the rear of the property, creating a new external sunken terrace. Finally, light the space professionally, including uplighters and downlighters to bounce valuable light around.

Basement room


Some of the largest properties come with surprisingly miniature kitchens, allocated in the days when cooking was done behind closed doors. Reconfiguring your existing space, and stealing extra inches from a wide hallway, unused storeroom or internal garage in the process, will usually prove far easier, quicker and affordable than any new-build project.

If your kitchen and dining/living rooms are still separate, knocking through to achieve the open-plan dream is one of the simplest ways to transform your cooking space. Even if the work requires steel supporting columns, it is still a fairly straightforward proposition and can be incredibly effective.

Basement conversions

(Image credit: Jonathan Gooch)


So just how do you make the most of a basement space? First of all, consider how you arrive in the room. 'Then try to keep the space as open plan as possible, to allow the available natural light to flow through the room,' advises Kieron Bell of Kitchens International. Use the areas with the most light for the cooking and dining areas where you will spend most of your time, and those furthest from the natural light for ancillary rooms, such as laundry and utility areas, pantries and storage. Glass partitions, rather than solid walls, will ensure the best light flow through the space.

Basement ideas

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If you live in a property without a garden and you are therefore unable to install a light well, a lack of natural light can be an issue. However, this can be overcome with the use of strong glass panels in the floor above, which can be walked on, particularly near windows or glass doors. It’s also worth considering glass balustrades, which will bring some light into the space. These darker basement area are ideal for media or cinema rooms, as well as utility rooms, gyms and studies.

Basement conversions

(Image credit: Jonathan Gooch)


A basement level will increase your living area and add value to your home, without using valuable garden space. If you already have a cellar, then a conversion is all that’s required. The floor level can be reduced to allow for extra headroom and light wells added to brighten the layout. Basements can be created retrospectively too, but this will be more costly. This space cleverly makes use of natural and artificial light to create a multifunctional room.

Basement room

(Image credit: Davide Lovatti)