A kitchen extension in London is the same construction as anywhere else and a different project. The difference is not the rate a builder charges, it is that the constraints arrive earlier and there are more of them: a shared boundary on at least one side, no side access, a conservation area more often than not, and a skip that needs a permit before it can stand on the street.
Access is the first cost, not the last
On a terrace with no side passage every bag of sand and every barrow of spoil goes through the house or over the roof of the existing rear projection. That changes the programme, the protection needed inside, and often the plant that can be used. Where a crane or a conveyor is needed, a road closure or a licence follows. This is the single biggest reason a London price looks different from the same drawings elsewhere.
Party walls come before planning
Most inner London kitchen extensions sit against at least one neighbour and involve excavation within the distances the Party Wall etc. Act cares about. Notices have response periods, and a dissenting neighbour means surveyors and an award. None of it is unusual and all of it takes time, so it belongs at the start of the programme rather than three weeks before the digger arrives.
Conservation areas and article 4 directions
Large parts of London are covered by conservation areas and some boroughs have removed permitted development rights by direction in particular streets. That does not stop the work, it means an application where a certificate would otherwise have done. Check the designation and any direction on the borough's own map before assuming your neighbour's precedent applies to you.
The western commuter belt is a different plot shape
Move out to the Thames suburbs and the constraint changes character. Plots are wider, side access often exists, and the party wall issue softens. In exchange you meet flood zone questions on the river side, larger gardens with mature trees and their root protection areas, and boroughs whose design guidance on rear extensions is specific. The construction is easier and the consenting is no simpler.
Kitchen extensions Weybridge and kitchen extensions Twickenham: the outer suburbs
Out here the stock is mostly interwar and post war semi detached and detached with side access and a garden that will take a rear extension without swallowing it, which is an easier build than the inner London terrace this page is mostly about. Two things still bite. Both areas carry conservation areas and, in places, article 4 directions, so the permitted development route you would expect is not guaranteed. And ground conditions vary enough across the Thames terraces that the foundation depth is a real variable rather than a standard figure, so ask for the foundations to be priced after a trial hole rather than assumed.
A single storey kitchen extension with skylights, and what the roof adds
Rooflights are what stop a deep rear kitchen from being dark at the back, and they are a structural and a thermal decision rather than a finish. Each opening needs trimming into the roof structure, so the size and position want settling at design stage and not on site. The glazing specification matters more than on a wall: a large horizontal or shallow pitched pane gains a great deal of heat in summer, so ask what the coating is and whether solar control glass is included in the price or offered as an upgrade later. Ask also how the upstands are detailed, because rooflight kerbs on a flat roof are a common source of leaks.
Questions people ask about kitchen extensions London
Why do London quotes vary so widely?
Because access, parking, permits, waste removal and party wall work vary hugely street by street, and different builders make different assumptions about all five.
Do I need a skip permit?
If the skip stands on the public highway, yes, from the borough. Where there is no off street space this is a recurring cost through the build.
Does a conservation area stop a rear extension?
Rarely. It usually means a planning application and more attention to materials, roof form and glazing than a certificate would have required.
Are trees a real constraint outside the city?
Yes. A protected tree or a root protection area can determine the foundation type and the position of the new wall, so establish it before the design is fixed.