Types of House Extensions: Which One Is Right for Your London Home? (2026)

London homes are notoriously short on space — but most of them have more potential than their owners realise. Whether you have a narrow side return, a usable rear garden, or unused roof space, there is likely an extension type that can transform how you live.

At NGC Build, we help London homeowners navigate their options and build extensions that genuinely change their lives. This guide covers every main type of house extension, what each one delivers, and which might be right for your home.

1. Rear Extension

A rear extension is the most popular type of house extension in London. It extends the back of your home into the garden, typically on the ground floor, creating more kitchen, dining, or living space.

• Average cost in London: £60,000 – £140,000+

• Typical use: open-plan kitchen-diner, living room, family room

• Planning: often falls under permitted development if within size limits

• Best for: most London property types with rear gardens

Under permitted development rights, a single-storey rear extension can extend up to 3 metres from the rear wall of a semi-detached or terraced house, or up to 4 metres for a detached property, without requiring planning permission. Larger extensions require a full planning application.

2. Side Return Extension

Many London terraced and semi-detached houses have a narrow strip of unused land running along the side of the property — the side return. Extending into this space is one of the most efficient ways to gain usable square footage without eating into your garden.

• Average cost in London: £45,000 – £110,000

• Typical use: widening the kitchen, adding a utility room, improving layout

• Planning: usually permitted development if kept to one storey

• Best for: terraced houses in London with a narrow side alley

Roof lights are essential in a side return extension to bring daylight into what would otherwise be a dark corridor-like space. Done well, a side return extension can make a standard London kitchen feel dramatically more generous and light-filled.

3. Wraparound Extension

A wraparound extension — sometimes called an L-shaped extension — combines a rear extension with a side return extension in one unified structure. It is the most transformative single-storey option available to most London homeowners.

• Average cost in London: £95,000 – £200,000+

• Typical use: large open-plan kitchen-diner-living, utility room

• Planning: usually requires full planning permission

• Best for: terraced and semi-detached London homes with both side return and rear garden space

The wraparound format gives you maximum flexibility in how you lay out your ground floor, and is particularly popular in boroughs such as Islington, Hackney, Wandsworth, and Lambeth.

4. Double-Storey Extension

A double-storey extension adds space on two floors simultaneously — typically extending the rear or side of the property upwards as well as outwards. It delivers the best cost-per-square-metre value of any extension type because foundations and roofing are shared across both floors.

• Average cost in London: £3,200 – £4,800 per m²

• Typical use: extra bedrooms and bathrooms upstairs, larger kitchen or living room downstairs

• Planning: always requires full planning permission

• Best for: families needing both ground floor space and extra bedrooms

For families outgrowing their home, a double-storey extension is often a better investment than moving — adding significant space and value without the huge transaction costs of buying a larger property in London.

5. Loft Conversion

A loft conversion transforms unused roof space into a liveable room — typically a bedroom, bathroom, home office, or a combination. It is one of the most popular home improvements in London precisely because it adds space without touching the garden or the ground floor footprint.

• Average cost in London: £55,000 – £100,000+

• Typical use: master bedroom with en-suite, home office, guest room

• Planning: dormer and hip-to-gable conversions usually permitted development

• Best for: homes with sufficient roof height and a desire for extra bedrooms

NGC Build has extensive experience in loft conversions across London, from straightforward Velux conversions to full dormer and mansard builds.

6. Single-Storey Side Extension

Where there is more land on the side of a property than just a narrow return, a full single-storey side extension can create an entirely new room — a home office, a playroom, a ground-floor bedroom or bathroom, or a garage.

• Average cost in London: £45,000 – £100,000+

• Typical use: new room, garage, home office

• Planning: permitted development if single-storey and less than half the width of the original house

• Best for: detached and semi-detached homes with usable side land

Which Type of Extension Is Right for Your London Home?

The right extension depends on your property type, your plot, your budget, and what you most need from your home. Here is a simple guide:

• Want more kitchen and living space? → Rear or wraparound extension

• Have a narrow side return? → Side return extension

• Need extra bedrooms? → Loft conversion or double-storey extension

• Want maximum space on a tighter budget? → Loft conversion

• Need the most dramatic transformation? → Wraparound or double-storey extension

How Much Does a House Extension Add to Property Value in London?

A well-designed extension can add between 10% and 25% to the value of a London property — and in some cases more, particularly in high-value boroughs. The key is quality design and construction. A poorly built or poorly designed extension can actually deter buyers, which is why choosing the right design and build company matters.

Talk to NGC Build About Your Extension

At NGC Build, we have delivered house extensions of every type across London. Our full design and build service takes your project from first sketch through to completion — covering planning permission, structural engineering, construction, and fit-out.

If you are not sure which type of extension is right for your home, our team will give you honest, expert advice based on your property and your goals. Get in touch today for a free consultation.

• All extension types covered: rear, side, wraparound, double-storey, loft

• Full design and build service across all London boroughs

• Transparent pricing and end-to-end project management

• Proven track record of quality London extension projects