Last Updated on November 4, 2026 by Blitz
The single storey rear extension is the most popular way to add space in South West London, and Putney is full of the Victorian and Edwardian houses it suits best. But in SW15 the same extension can be a straightforward permitted development job on one street and a full planning application on the next.
The difference is not the design. It is the address. The architects putney homeowners work with spend the first conversation sorting exactly this, because it decides the timeline, the cost and the risk.
Here is what falls into the simple column, and what tips into needing an application.
The Simple Column: Permitted Development in Putney
Across much of central Putney, outside the conservation areas, houses keep their full permitted development rights. That is the simple end, and a lot of SW15 sits here.
A single storey rear extension usually qualifies as permitted development when it stays within the limits: up to 3 metres beyond the original rear wall for a terraced or semi detached house, or 4 metres for a detached one. Height is capped at 4 metres, and it cannot cover more than half the land around the original house.
Hit those limits on an unconstrained Putney street and you do not need a planning application at all. You can build, and then obtain a Lawful Development Certificate as written proof the work was lawful, which a buyer’s solicitor will want later.
There is even a route to go bigger without full planning. The Larger Home Extension Scheme allows 6 metres on a terrace or semi, and 8 on a detached house, through prior approval. That is not quite as simple, because it brings in a neighbour consultation, but it stops short of a full application.
The Application Column: When Putney Gets Complicated
Now the other side. Several things push a Putney single storey extension out of permitted development and into a full application to Wandsworth Council.
The big one is conservation areas. Putney has several, including Putney Embankment, West Putney and Lower Common, concentrated on the riverside and the older streets. Inside a conservation area, side extensions stop being permitted development, the larger 6 metre rear route is removed, and even a modest scheme faces design scrutiny on materials and the building line.
Then there are the property specific triggers that apply anywhere in SW15:
- Flats and maisonettes, which have no permitted development rights for extensions at all
- Houses that have already used up their allowance through previous extensions
- Any Article 4 direction on the specific address
- A scheme that exceeds the size limits, or projects beyond the front elevation
Any one of these, and you are filing a householder planning application, where the fee is £548 and the council assesses the design rather than just checking dimensions.
Why Two Neighbours Get Different Answers
This is what surprises Putney homeowners most. You can stand in your kitchen, look at an identical house three doors down with a lovely rear extension, and still find you need permission where they did not.
It happens because the conservation area boundary runs down the middle of many Putney streets, or because one house is a flat and the other a whole house, or because a previous owner already extended and spent the allowance. The houses look the same. Their planning positions are not.
So a neighbour’s finished extension tells you what was possible at their address, on their history. It is not a reliable guide to yours.
The Check That Settles It Before You Spend Anything
The single most useful thing you can do, before commissioning a design or taking a builder’s quote seriously, is establish which column your address is in.
That means three quick checks. Whether your property sits inside one of Putney’s conservation areas. Whether any Article 4 direction applies to it. And what the planning history shows about previous extensions and any conditions attached to them. All three are matters of record, and all three change the route entirely.
Get this wrong and the cost is real. People design a 6 metre extension, fall in love with it, then discover their conservation area street caps them at a smaller full application scheme, and the drawings have to start again.
What a Putney Single Storey Extension Costs
Whichever column you land in, the build itself is priced after a survey, because SW15’s period houses hide variables. As a 2026 guide,a single storey rear extension in Putney commonly starts around £50,000 for the build at the simpler end, and once design, planning, a quality finish and VAT are included, all-in figures for a larger scheme can run well into six figures. The spread is wide, which is exactly why a Putney extension is priced after a survey rather than off a headline rate.
The planning route affects the total too. A permitted development scheme saves the application fee and several weeks. A full application in a conservation area adds the fee, the design work to satisfy officers, and time.
Two costs people forget on Putney terraces: the structural work to open up the rear, which needs calculations for Building Control, and the party wall process with neighbours on a terrace. Neither is optional, and both are cheaper to plan for early than to discover mid build.
Getting a Putney Extension Right
The pattern across smooth Putney projects is that the planning position is settled first, the structure is understood early, and the design is shaped to fit both. A good single storey extension in SW15 is one designed around what the specific street and house actually allow, rather than a scheme drawn in hope and corrected later.
This is where having the right team matters. Extension Architecture runs architects, planning consultants and in-house structural engineers under one roof, so the conservation check, the design and the structural calculations move together rather than being handed between separate firms. On a period Putney terrace, that coordination is what keeps a project from stalling halfway.
The SW15 Takeaway
A single storey extension in Putney is genuinely simple on many central streets, and genuinely involved on the riverside and conservation streets. The build is similar either way. The paperwork is not.
Before you plan anything, find out which Putney you are in. If your street sits outside a conservation area and your house keeps its rights, you may be closer to breaking ground than you think. If it sits inside one, the project is still very achievable, it just starts with an application and a design made to earn its approval. Either way, knowing which column you are in is the difference between a project that runs to plan and one that resets halfway through.
