Basement conversions: the ultimate guide to converting a basement

A basement conversion might be the best way to add space and value to your home if you don’t have the room to extend above ground. This three page feature tells you all you need to know about how to convert a basement

Basement conversion: kitchen diner and living space in a basement extension to a Victorian home with a golden retriever
(Image credit: Simon Maxwell)

Designing a basement conversion carefully is really important in ensuring that the new room feels like a natural part of the existing house, that it's flooded with natural light, that it doesn't feel enclosed or claustrophobic, and that each of the rooms' proportions is as good as can be. 

Use these design tips below to get your basement conversion just right.

Introducing natural light to a basement

A well-lit basement living space, with access to the back garden will add lots more value to your home than a dingy converted cellar space with low headroom. 

Light wells or skylights are the most obvious way of introducing light and ventilation into a basement. There are potential planning issues – notably within Conservation Areas – but there are design solutions for most situations. A small opening with a walkable grill over it can make a big difference to the feel of a basement space, and add real value. Larger openings can have a protective covering in toughened glass.

kitchen diner and living space in a basement extension to a Victorian home with a golden retriever

(Image credit: Simon Maxwell)

If space is limited, you could include a sunpipe that uses glass panels and angled mirrors, to bring natural daylight down into your basement. Equally clever solutions include light-ducts and hi-tech fibre-optic cable systems, where special light fittings are linked via fibre-optics to a solar collector on the roof that will track the path of the sun and feed light down to the rooms below.

Glazed ceiling panels in the ground floor above are another way to bring down borrowed light and suit more contemporary properties, while you may want to consider installing glazed doors – either sliding or bi-fold – out to the garden if the design of your basement allows.

Simple tricks such as painting the walls of any lightwells in bright white and keeping garden foliage above neatly trimmed will help natural daylight travel down into your basement space, too.

Choosing doors and windows for your basement conversion

The style of any doors and windows should be matched to those of your existing home for a cohesive look – or to those of the basement's architecture if it's designed to contrast. You may have little choice about their positions, sizes and shapes, but you can get the framing materials and sightlines just right. 

Go for the widest panels and the slimmest framing materials possible, especially for bi-fold doors; doing so will give you uninterrupted views into a garden or submerged terrace, and will allow in plenty of light, too.


(Image credit: Chris Snook)

Consider basement ceiling heights

The ceiling height in a basement should, ideally, be in proportion to those of the house above. They may not match those of the ground floor living spaces, but it should at least match those of the bedrooms on the first floor. Keeping the ceiling heights the same within the basement will help it feel well designed, too. 

What is the minimum ceiling height? There isn't one defined under building regulations, other than above staircases, but 2.3m to 2.4m is standard. 

Bear in mind that increasing ceiling height by reducing the floor level of an existing basement is treated as an extension and so may need planning permission. 

Fitting out the basement's interior

The interior layout is an important part of designing a basement conversion. Whether you go open-plan or create a series of smaller rooms largely depends on the structure itself, available daylight at each end of the basement and your needs. 

As well as thinking big picture – how you will use the room – consider the details, too. For example, matching the design of the staircase to that of the one going up to the first floor will help the basement feel like a natural part of the house. Similarly, picking skirting, coving, mouldings, doors, flooring... that echo those of the rest of your home will also make the new space feel like it's always been there.

Lastly, consider the lighting carefully. It's likely, despite your best efforts, that the basement rooms are darker than those in the rest of your home. So, ensuring the that right type of light (with daylight-mimicking lightbulbs, for example) reaches potentially dark corners as well as the main spaces and that lighting is on more than one ring so that you can provide different light levels depending on how the room(s) are being used, is vital.

Using our tips on designing a north-facing room will be invaluable in making the most of the natural daylight.

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