House Extensions · London
Rear extensions, side returns, wrap-arounds and double-storey additions across London - designed with a considered architectural eye and managed from concept through to planning permission and beyond.
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What We Do
Rosace Design Studio designs and builds house extensions across London and a 30-mile radius. We are an architecture and construction practice, which means you get one team from the first sketch through to the finished build. No separate builder to find, no gap between what the architectural designer draws and what the contractor delivers.
Most of the homeowners we work with come to us because they have outgrown their house but love the area they live in. The kitchen is too small, the ground floor is too dark, or there is simply not enough room for how their family lives now. A well-designed extension solves all of that without the cost and upheaval of moving.
As residential architectural designers in London, we bring the same considered approach to a kitchen extension in Hackney as we do to a full rear and basement scheme in Mayfair. We do not impose a signature style onto your home. Instead, we listen to how you live, study the building, and design a space that feels like it was always meant to be there.
We handle everything in-house: architectural design, planning applications, building regulations, structural engineering coordination, interior specification, and construction. One contract, one point of contact, one team that is accountable for the whole project.
Types of Extension
Rear extensions are the most common type of house extension in London. They push the back of the house out into the garden, typically by 3 to 6 metres, creating a larger kitchen or open-plan kitchen-dining-living space. On terraced and semi-detached houses, a single-storey rear extension up to 3 metres deep often falls under permitted development, meaning no planning application is needed.
Side return extensions are particularly popular on Victorian and Edwardian terraced houses, where a narrow alley runs down one side of the property. A side return infill reclaims that wasted space and is usually combined with a rear extension to create a much wider ground floor.
Wrap-around extensions combine a rear extension with a side return into one L-shaped addition. This is often the most transformative option for terraced houses, turning a cramped galley kitchen and dark dining room into a single, generous, light-filled space.
Double-storey extensions add space on both ground and first floor levels. They require full planning permission but offer significantly more square footage for a relatively modest increase in cost compared to a single storey. A double-storey extension is often the most cost-effective way to add both living space and an extra bedroom.
Kitchen extensions focus specifically on the kitchen and dining area. Many London homes have kitchens that were built for a different era. A well-planned kitchen extension opens the room up, brings in natural light, and connects it to the garden in a way that completely changes how the ground floor works.
For guidance on extending period properties specifically, read our guide to extending a Victorian terrace in London. Every project also includes 3D visualisation so you can see the finished design before construction starts.
Planning & Regulations
Not every house extension needs planning permission. Under permitted development (PD) rights, single-storey rear extensions up to 3 metres deep on attached houses, or 4 metres on detached houses, can usually be built without a formal planning application. Larger extensions of up to 6 metres (attached) or 8 metres (detached) may be possible through the Prior Approval process.
However, London has a high concentration of conservation areas and Article 4 Directions that restrict or remove PD rights entirely. If your property is in a conservation area, or the extension is visible from a public highway, or it exceeds PD size limits, you will need full planning permission. We check all of this at the start of every project so you know exactly where you stand.
Rosace Design Studio prepares and submits planning applications to councils across London. We know what each borough expects, from Camden's strong design policies to Richmond's sensitivity around conservation areas. Our applications include full architectural drawings, design and access statements, and any supporting documents the council requires. We handle all correspondence with the case officer throughout the process.
Cost Guide
Construction costs for house extensions in London typically range from £2,200 to £3,500 per square metre, depending on the specification, the complexity of the build, and the area. Central and prime London boroughs tend to sit at the higher end due to access constraints and the quality of finish expected.
As a rough guide for 2026: a single-storey rear extension of around 15 to 20 square metres usually costs between £50,000 and £80,000. A wrap-around combining rear and side return typically falls between £70,000 and £120,000. A double-storey extension adds roughly 50 to 70 percent more than a single storey of the same footprint, but gives you significantly more usable space.
Because Rosace Design Studio handles both architecture and construction, our pricing is transparent from early in the design process. We provide cost estimates before you commit to a planning application, so you are not designing something you cannot afford to build.
For a detailed breakdown of what extensions cost in London, including a borough-by-borough comparison, read our house extension cost guide for 2026.
Cost Calculator
Tell us the size, location and finish level. Our calculator returns a realistic range for your extension or loft conversion, with a detailed breakdown available.
Why Rosace Design Studio
The biggest frustration homeowners have with house extensions is coordination. The architectural designer designs something, the builder says it will cost more than expected, and neither takes responsibility for the gap. Meanwhile, the project stalls and costs climb.
Rosace Design Studio eliminates that problem entirely. We are both the design studio and the builder. Our design team creates the drawings, and our construction team builds from them. There is no handover gap, no miscommunication between firms, and no finger-pointing when something needs resolving on site.
This model also means you get realistic cost guidance from day one. We design with buildability and budget in mind, because the people drawing it work alongside the people who will build it. The result is fewer surprises, tighter programmes, and a finished extension that matches the design intent.
Coverage
Rosace Design Studio works across all of Greater London and within a 30-mile radius. We have completed extension projects in boroughs including Kensington, Chelsea, Wandsworth, Islington, Hackney, Camden, Hampstead, Richmond, and Wimbledon.
Outside London, we regularly take on projects across Surrey, Hertfordshire, Essex, Kent, and Buckinghamshire. If you are within our coverage area and considering an extension, we would be happy to visit the property and talk through what is possible.
How It Works
01
Site Visit
We visit your property, discuss your brief and budget, and give you an honest assessment of what is achievable. We check the planning position and flag anything that could affect the project before you commit.
02
Design Development
We develop two or three design options at different scales and budgets, so you can see what is possible and make an informed choice. Once you settle on a direction, we refine it into a full set of drawings ready for planning.
03
Planning & Approvals
We prepare and submit the planning application or permitted development notification, handle all correspondence with the council, and coordinate with structural engineers and party wall surveyors as needed.
04
Build & Handover
Our in-house construction team builds the extension. We manage the programme, handle building regulations sign-off, and keep you informed throughout. You get one point of contact from start to finish.
Common Questions
