20 extension design ideas

Property and renovation expert Michael Holmes, shares his tips for designing an extension that is both beautiful and functional

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A glass box extension draws natural light into the interior of this mid-terraced house

1. Make the most of natural light

As well as maximising the number of windows and exterior doors in your extension, consider other options such as rooflights, roof lanterns or a clerestory – a row of windows set just below ceiling level – all of which will bring as much light into the space as possible.

2. Change your whole layout

When you’re adding an extension, it’s worth taking the time to reconfigure your existing room layouts to make the most of the space as a whole. Think about which spaces need the most natural light and how you will make best use of your views. Consider how you will use the spaces carefully – for instance, you don’t want your dining table at the opposite end of the house to your kitchen. Internal walls and doorways can be added or removed relatively easily to ensure the extension integrates with the existing space.

3. Consider two storeys

If you are looking for maximum value for money, consider building your extension over two storeys, rather than one. You’ll reduce the average cost per square metre by making the expensive structural elements – such as the roof and foundations – cover more useable space.

two storey rear extension with glazed gable

This modern two-storey rear extension was built without need for planning permission

4. Think about the style

Choose either a contrasting but complementary style, or make the extension look like it has always been there. If you decide to create a seamless extension, which is the more difficult option, make sure you copy the key design elements such as roof pitch, materials and even things like mortar.

5. Integrate your lighting

Think about lighting from the outset. A well-planned lighting scheme will need different circuits for different activities and will need to be incorporated into the build. As well as ambient lighting to provide basic background light for everyday tasks, include accent lighting in the form of directional spotlights, up-lights and down-lights. When work is complete, you can introduce complementary task lighting in the form of lamps.

6. Use structural glazing

If you’re thinking of extending a period home, one option is to add the new space as a separate building linked to the original house through a glazed walkway. This not only reduces the visual impact, but also leaves the original building’s character unaltered, which is favoured by many conservation officers.

7. Open-plan with a difference

If you’re not sure an open-plan space is for you, think about fitting sliding pocket doors, which will give you the best of both worlds. Sliding flush doors can give the appearance of a wall when closed, but then pull back within the actual wall space to create a clear opening.

kitchen link to corridor with chalk board painted sliding door

A blackboard-painted sliding door saves space and doubles as a drawing wall for the children in this 1960s remodel

8. Keep some privacy

Using lots of glass to maximise on natural light is key to a successful extension design; however, you may need some privacy if a new window opens out onto a neighbour, the street or a side alley. Consider using obscured glazing, such as textured, sand-blasted or acid-etched glass, so you get the benefit of daylight but without anyone being able to look in or out.

9. Add a feature fire

There’s no need to add a traditional open fire thanks to two contemporary alternatives, both of which offer the feature and comfort of real flames, but are more energy-efficient. A room-sealed woodburning stove, connected to an internal air source to prevent any draughts, is highly energy efficient and comes in all kinds of designs, from traditional to contemporary. Flue-less gas fires, meanwhile, are 100% energy efficient and require no chimney or flue.

10. Include high ceilings

Open-plan spaces, in particular, benefit from high ceilings. An extension makes it possible to incorporate a tall ceiling height into your home for relatively little cost, either by digging down or building up. If you’re adding two storeys, consider a higher ceiling downstairs and introduce a split-level floor upstairs to link the original building to the new. It’s also worth considering adding a pitched roof, which will need insulating differently to a standard flat ceiling.

double height living area with mezzanine level in extension

A dramatic open-plan space has been created in this two-storey extension and enhanced with a double-height ceiling. This has allowed the inclusion of a mezzanine level to zone the living area

11. Think about soundproofing

If you’re aiming for a contemporary design, you’ll need to consider adding sound-absorbent materials into the space. Surfaces such as glass, polished stone and concrete look sleek but allow sound to reverberate around the space, making it feel cold. If rugs, curtains and other soft furnishings aren’t to your taste, you can fit acoustic panels, which are designed to look like wall art.

12. Add a sunroom, not a conservatory

Some extensions, such as smaller conservatories, don’t require planning permission, are excluded from Building Regulations, and are fairly inexpensive to build. However, they tend to be thermally inefficient, being too hot in the summer and too cold in the winter. An alternative is to build a sunroom, which still has large areas of glazing but with a conventional insulated roof and at least one insulated wall, usually facing a boundary.

13. Frame the best views

Take a look outside and decide which areas you want to see the most of and which you want to view the least. You can then position your windows to frame the best views and improve privacy. Think about the shape of the windows, too, as long, narrow windows can create panoramic views across a particularly pleasing landscape. If you’re adding a bedroom or living room, use low-level windows to create views when lying or sitting down.

white contemporary kitchen in an extended home

A contemporary kitchen extension was added to this Victorian home and connected via a glazed link, creating a light filled central courtyard

14. Plan your kitchen carefully

The majority of extensions are used to create open-plan kitchen-dining-living spaces. If this is the case, you also need to think about the kitchen layout at the same time as the build itself. Consider whether you really need natural light in your kitchen or whether it would be better located at the back of the space, with clever lighting, which will allow your living and dining areas to be located closer to the windows, maximising any views. It’s also worth considering adding a stud wall to create a utility space or pantry.

15. Consider an annexe

An extension doesn’t always have to be linked to the main house. Depending on the size of your garden, an annexe may be the best solution. This is particularly true if you’re looking to create self-contained accommodation for family members of visitors, as you can incorporate living, bedroom, bathroom, and kitchen spaces.

renovated gardener's cottage used as a modern annexe

A dilapidated gardener’s cottage was renovated to create this annexe to a Hampshire home

16. Add a design feature

Cantilevering – where a rigid structural element, such as a beam, is anchored at only one end so it protrudes out – is a useful way to create balconies, mezzanines or whole storeys that appear to float with no visible means of support.

17. Don’t forget your staircase

If you’re adding a two-storey extension or mezzanine, you may need to introduce a new staircase. Rather than making it purely functional, consider creating an architectural feature with open treads, glass balustrades or a sweeping shape. You can incorporate clever lighting to highlight the design, too.

18. Transform your home’s exterior

Instead of worrying about making an extension complement your existing property, you could consider a complete exterior transformation that lets the extension blends seamlessly with the original structure. Popular options include wood cladding, metal cladding or rendering, all of which can help bring character to buildings that are unattractive or have been extended unsympathetically in the past.

oak frame home with large glazed sections to garden

This stunning oak frame addition was created as part of an extension and remodel project on a 1960s home

19. Use an oak frame in your build

Oak-frame extensions have become hugely popular, particularly for rustic or period homes. A vaulted ceiling with exposed beams is a stunning design feature and instantly adds character to any room. To keep costs down, consider combining an oak roof structure with softwood rafters as these can be hidden behind plasterboard and masonry.

20. Link with the outside

Consider creating an outdoor living/cooking area to link your extension to your outside space. It’s worth planning a projected flat roof above the space to ensure some protection from either too much sunshine or light summer rain.

outdoor indoor space to Australian style bungalow with hanging chair

After returning to the UK from Australia, the owners of this bungalow were keen to recreate the indoor/outdoor spaces they had in their last home