Extension types we design
- Single storey rear — the most common London extension: a new kitchen, dining or living space opening onto the garden.
- Double storey rear — adds a room above as well, usually a bedroom with an ensuite, where the ground floor needs and the upper floor needs can be solved together.
- Side return — uses the narrow strip beside a terraced house, often combined with a rear extension to create one wider space at the back.
- Two storey and wrap-around — a larger footprint that wraps around the side and rear, generally the most planning-sensitive of the group.
Planning for extensions
Single storey rear extensions are frequently permitted development, within limits that depend on the house: broadly three metres beyond the rear wall for a terraced house and four metres for a semi-detached or detached house, subject to height and boundary conditions. A larger single storey extension can be built under the prior approval route, which is a lighter process than a full application but is not automatic.
Two storey extensions sit under stricter permitted development limits, and conservation areas, Article 4 directions and flats usually require a full application. Because extensions are where neighbours are most affected, we design with overlooking, daylight and boundary distances in mind from the first sketch rather than discovering the objection at committee.
Not sure what your property needs?
Send us the address and what you are trying to achieve. We will tell you what is likely to be possible, what approvals it involves, and what the design work would cost.
Structural design for extensions
Removing the rear wall to open a house up to its extension means carrying the load that wall used to take. That is a structural question, not a drawing question, and the answer is normally steel.
- Steel beam design for the opened rear wall, including the bearings and padstones at each end.
- Foundation design for the new footprint, matched to the ground conditions and to the existing house.
- Roof structure for flat, pitched or glazed roofs, and the junctions where the new roof meets the old.
- Calculations for any internal knock-throughs that form part of the same project.
Building regulations
Extensions are subject to the building regulations in full. Our building regulations drawings and calculations cover the structure, thermal performance of the new envelope, damp proofing, drainage and the glazing, and we coordinate with building control through the inspection stages.
Where we work
We work across London and the surrounding areas, including Tower Hamlets, Newham, Hackney, Islington, Redbridge, Waltham Forest, Barking and Dagenham, Greenwich, Lewisham, Southwark, Camden, Haringey, Enfield, Barnet, Ealing, Brent, Harrow, Hillingdon, Richmond, Kingston, Merton, Wandsworth, Lambeth, Croydon, Bromley, Bexley, Havering, Westminster, Kensington and Chelsea, and Hammersmith and Fulham.
Frequently asked questions
Do I need planning permission for a rear extension?
A single storey rear extension is often permitted development, broadly within three metres for a terraced house and four metres for a semi-detached or detached house, subject to height and boundary conditions. Larger single storey extensions can use the prior approval route. Conservation areas, Article 4 directions and flats normally require a full application, so the position has to be checked for your address.
Can I extend a flat or maisonette?
The planning position for flats is different from houses: permitted development rights for extensions generally do not apply, so a full application is normally needed, and the freeholder's consent usually is too. We can still design and submit the scheme, but the lease and freehold position needs checking early.
How much will my extension cost?
Build cost depends on the footprint, the roof, the glazing and the ground conditions, and design fees depend on the size of the scheme and what approvals it needs. We price the design and submission work for your project specifically rather than quoting a figure that would not hold.
Will my neighbour's consent be needed?
Not for planning permission itself, but their objection can influence the decision, and works near a shared boundary or party wall bring the Party Wall etc. Act 1996 into play. We design to avoid the common objections and tell you early if a party wall award is likely to be required.
Do you handle the planning application and building control?
Yes. We prepare and submit the drawings, liaise with the council on the application, and produce the building regulations drawings and structural calculations that building control needs. You are not left coordinating three separate professionals.
Planning and building regulations guidance on this page is general and applies to England. The position depends on your property, its history and your council's policies, so it is not a substitute for advice on your address. We check the specifics before any work begins.