LET-HD Developments designs and builds house extensions across London. We manage the whole project in house, from the first survey and architectural drawings through planning and building control to the finished open-plan space, so you deal with one team from start to finish.
An extension is one of the best ways to add space to a London home. It lets you create an open-plan kitchen and dining area, add a bedroom or bathroom, and improve the flow between the house and the garden, all without moving.
We work across London and the surrounding areas, including Hackney, Islington, Walthamstow, Wanstead, Woodford, Ilford, Romford and Stratford.
Why extend your home?
- Add space without moving house, saving on stamp duty and moving costs.
- Create the open-plan kitchen and living space most London homes lack.
- Improve the connection between the house and the garden.
- Add a bedroom or bathroom with a double-storey extension.
- Increase the value of your property.
Types of extension
The right extension depends on the shape of your home, your garden and the space you need. These are the four types we build most.
Single-storey rear extension
The most common extension in London. A new ground-floor room built out from the rear wall, usually as an open-plan kitchen, dining or living space. Often permitted development.
Side-return extension
Infills the narrow alley beside the kitchen of a Victorian or Edwardian terrace. It adds valuable width and light and is usually combined with a rear extension. Often permitted development.
Wrap-around extension
A side-return and rear extension built as one, wrapping around the back corner of the house for the largest possible ground-floor footprint. Usually needs full planning permission.
Double-storey extension
Two floors built as one structure, adding a bedroom or bathroom above the new ground-floor space. The best value per square metre, because the foundations and roof are shared. Almost always needs planning permission.
Our process
Free survey and quote
We visit, discuss what you want to achieve, and give you a clear written quote.
Design and structural calculations
We prepare the drawings and structural calculations. We can work with your own architect if you prefer.
Planning and building control
We advise whether you need planning permission and handle the building control application.
Groundworks and structure
Foundations, drainage, steels and the shell, completed and made weathertight.
Fit-out and finish
Electrics, plumbing, plastering, glazing and decoration, through to building control sign-off.
Do you need planning permission?
Many single-storey rear and side-return extensions are covered by permitted development, which means no planning application is needed, provided they meet the limits (for example, no more than 3 metres deep for a terraced or semi-detached house, or 4 metres for a detached house, and no more than 4 metres high).
You will usually need planning permission for a wrap-around extension, for a double-storey extension, if your home is a flat, or if it is in a conservation area or under an Article 4 direction.
Every extension needs building regulations approval, and the Party Wall etc. Act 1996 applies where you build against or near a neighbour’s property, which is common on London terraces. We explain exactly what applies to your project at the survey stage.
What does a house extension cost in London?
Costs depend on the type, size and specification. As an indicative guide to 2026 London build rates:
| Extension type | Indicative build rate | Typical size | Planning route |
|---|---|---|---|
| Single-storey rear | £2,200 – £3,400/m² | 12–30m² | Often permitted development |
| Side return | £2,400 – £3,600/m² | 12–18m² | Often permitted development |
| Wrap-around | £2,600 – £4,000/m² | 25–40m² | Usually full planning |
| Double-storey | £2,000 – £3,000/m² | 30–60m² | Usually full planning |
These figures are indicative 2026 London build rates and exclude kitchen and bathroom fit-out, architect, planning, party wall and building control fees, and VAT. Your free, no-obligation quote will be specific to your property and specification.
Why choose LET-HD
- One team, start to finish. We manage design, planning, building control and the build.
- Experienced and accredited. We are an established London builder and a member of recognised trade bodies (see our accreditations).
- Quality guaranteed. All our work is carried out by our own skilled tradesmen and is fully insured.
- Clear pricing. A detailed written quote, with no hidden extras.
See our extensions
You can see examples of our completed extensions and refurbishments on our Our Work page.
Frequently asked questions
How long does an extension take?
A single-storey rear extension typically takes 12 to 16 weeks on site, and a double-storey extension 20 to 26 weeks, once drawings and building control approval are in place.
Can I stay in my home during the work?
In most cases, yes. We keep the site secure and work in phases to limit disruption, though there will be a period when the rear of the house is open to the weather.
Do I need an architect?
You need drawings and, for most extensions, structural calculations. We can manage this for you, or work with your own architect if you prefer.
What is the cheapest way to add space?
Per square metre, a double-storey extension is usually the best value, because one set of foundations and one roof serve two floors. A side return adds valuable width to a terrace for a relatively modest footprint.
What areas do you cover?
We cover London and the surrounding areas. If you are not sure whether we work in your area, just call us on +44 (0) 203 355 5313.
Related guides
- Do you need planning permission for a house extension in London?
- Party wall agreements: a guide for London homeowners
- How much does a house extension cost in London? (2026)
Get a free extension quote
Call +44 (0) 203 355 5313, email info@lethd.com, or use our contact form. We will arrange a free survey and give you a clear, written quote.