The permitted development rules for rear extensions
On a house, a single-storey rear extension is permitted development if it projects no more than 3 m from the original rear wall on a terraced or semi-detached house, or 4 m on a detached house, is no higher than 4 m, has eaves no higher than 3 m where it comes within 2 m of a boundary, and uses materials similar in appearance to the house. The larger home extension route allows 6 m or 8 m through a 42-day prior approval, where the council consults the neighbours.
Flats and maisonettes have no householder permitted development rights, so any rear extension to a flat needs planning permission. Previous extensions count against the allowance, and the larger home extension route is not available in conservation areas.
What changes in Islington
In a conservation area a single-storey rear extension can still be permitted development within the 3 m or 4 m limit, but cladding it in materials that differ from the house is not, and the 6 m and 8 m prior approval route is closed.
The local constraints that most often decide the route in Islington are listed below, taken from our Islington area page. Each one is a reason to confirm the address on Islington's constraints map before relying on permitted development.
- Conservation areas. Around 40 conservation areas cover roughly half of Islington, including Barnsbury, Canonbury, Highbury Fields, Clerkenwell Green, Tufnell Park and Hillrise. Roof extensions and cladding in these areas need planning permission rather than permitted development. Check the council's constraints map for your address before assuming PD applies. Source
- Article 4 directions. Islington has a Class MA Article 4 direction covering the Central Activities Zone and its town centres, removing the commercial-to-residential prior approval route there, and Article 4 directions in several conservation areas removing permitted development for front alterations. We confirm coverage for your address with the council. Source
- Listed buildings. Barnsbury, Canonbury, Clerkenwell and the Georgian squares contain many listed terraces. Listed houses need listed building consent for almost any alteration, internal or external, and extensions to neighbours are judged on their effect on the setting of the listed terrace.
What Islington planning officers look for
Islington is one of the stricter London authorities on householder design and applies the Urban Design Guide closely. Rear extensions are generally expected to be single storey and no deeper than 3 m on terraces, side returns must keep parapets low against the neighbour's garden and roof extensions in conservation areas are frequently refused unless they follow an established pattern on the terrace. Mansards are accepted where the terrace already has them; front dormers are not. Pre-application advice is available for a fee and, in our experience, is worth using for anything in Barnsbury or Canonbury and for all basements.
Fees and timelines
The council fee for a householder application is £528 and for a Lawful Development Certificate £264 (England, from 1 April 2025; verify before applying). Both are decided within 8 weeks of validation.
Our own fee for the drawings and the application is fixed once quoted and depends on the project type, its size and the constraints above. Answer six questions in the quote tool and we email you an indicative figure within minutes, then a written fixed-fee quote within 24 hours.
