House extensions in North London, from the foundations to the kitchen.
Single and double-storey rear extensions, side returns and wrap-arounds, built with the structural engineer, the architect and Building Control lined up before the ground is broken. Bayocorp coordinates the consultants alongside our own trades so the drawings and the site work agree.
An extension is groundwork, structure and services before it is a room.
Most of what decides the cost and the programme of an extension sits below and behind the finished room: the foundations and what the ground turns out to be, the drainage that often runs exactly where the extension is going, the steelwork that opens the existing house into the new space, and the heating and electrics that have to be extended to reach it. We price those properly at the start rather than leaving them as allowances that grow.
Above ground it is the decisions that make the room work: the glazing, rooflights or a lantern, the floor build-up and whether it carries underfloor heating, and the kitchen layout that most rear extensions are built around. We fit kitchens from Wren Kitchens and Howdens, or a bespoke design of your own.
- Single-storey and double-storey rear extensions
- Side return and wrap-around extensions
- Foundations, drainage, structural steelwork and openings into the existing house
- Roofing, glazing, rooflights, bi-folds and underfloor heating
- Open-plan kitchen-diners and the finishes that tie the new and old together
Read more: 10 things that can increase the cost of a London house extension
Permitted development, prior approval and when you need a full application.
Some extensions to houses can be built under permitted development. The Planning Portal's limits for a single-storey rear extension are 3 metres beyond the original rear wall on an attached house and 4 metres on a detached one, no more than 4 metres high, and no more than 3 metres at the eaves within 2 metres of a boundary. A larger single-storey extension, up to 6 or 8 metres, is possible through the prior approval process, where the council is notified and neighbours can comment.
The limits tighten in a conservation area: every side extension needs householder planning permission, every rear extension of more than one storey does too, and cladding the outside is not permitted development. Flats and maisonettes have no householder permitted development rights at all. Much of inner North London is in conservation areas, so we check the address before anything is drawn to the wrong rules.
Party walls and building on the boundary.
A rear or side return extension on a terraced or semi-detached house often means building on or at the boundary, cutting into the party wall for steel, or digging foundations near the neighbour's. All of those are notifiable under the Party Wall etc. Act 1996. GOV.UK guidance is that notice is served between two months and a year before work starts. We plan the notices into the programme from the first meeting, because they set the earliest start date.
Building Control, dutyholders and the Principal Designer.
Planning permission or permitted development decides whether the extension can be built. Building Regulations decide how, and an extension brings several regulated elements together at once: the foundations, the steel opening into the existing house, drainage, the thermal performance of the new walls, floor, roof and glazing, and on a two-storey extension the fire escape from the upper floor. Building Control inspects at stages, so the programme is built around those visits.
The 2023 dutyholder rules apply to every extension: the client, the Principal Designer and the Principal Contractor are each named, with declarations at application and at completion. Where an architect has drawn the scheme but nobody has been appointed Principal Designer, we can take the role on under a formal appointment.
- Building Regulations application, inspections and the completion certificate
- Liaising with Building Control throughout the work, not only at the end
- Dutyholder forms completed at application and at completion
- Principal Designer role taken on by formal appointment where you have none
Read more: Building Regulations for structural alterations and extensions
Real extension work on the site today.
Our Acton case study combined a two-storey rear extension with converting the office space upstairs into a two-bedroom flat, above an estate agency that kept trading throughout. Structural work, new service routes and fresh water supply had to be threaded through the working shop below, which is the same discipline a rear extension needs on a terraced street with a family living in the house.
How Bayocorp runs the work.
Site visit and constraints
Ground, drainage, boundaries, access for materials and whether the street is in a conservation area. This decides the approval route before anything is drawn.
Design, engineer and approvals
We coordinate the architect and structural engineer, then planning or prior approval, Building Regulations and party wall notices in the right order.
Scope and cost plan
Priced from the drawings and the engineer's design, with the groundwork and drainage priced properly rather than left as an allowance.
Build and hand over
Foundations, structure, roof and glazing, services, then the kitchen and finishes, with Building Control inspections at each stage and the completion certificate at the end.
What changes across North London for an extension.
Terraced streets in Islington, Camden and Hackney tend to mean side returns, shared party walls on both sides and tight access through the house. Barnet and Enfield have more semi-detached and detached houses, where a wider extension or a wrap-around becomes possible and the permitted development limits are different. Either way the conservation area question comes first.
House Extensions questions we hear often.
How far can I extend without planning permission?
Under permitted development the Planning Portal limit for a single-storey rear extension is 3 metres on an attached house and 4 metres on a detached one, with height limits. Larger single-storey extensions can go through prior approval. Conservation areas and flats are treated differently, so we check your address first.
Do I need a structural engineer for an extension?
Almost always. The foundations, any steel opening the existing house into the extension, and the roof all need a structural design, and Building Control will expect calculations. We coordinate the engineer so the design and the build information agree.
Will the drains be a problem?
Often they are the first thing found. Rear extensions are frequently built over or beside the drainage that serves the house, and a public sewer can need the water company's agreement. We look for it at the first visit rather than when the ground is opened.
Do I need a party wall agreement for a rear extension?
If you are building on the boundary, cutting into the party wall or excavating near your neighbour's foundations, yes. Notice must be served in writing before work starts, and a neighbour who does not respond has not agreed. We build this into the programme.
Who handles Building Control and the dutyholder forms?
We do. We make the Building Regulations application, arrange the inspections, complete the dutyholder forms at application and completion, and where you have not appointed a Principal Designer we can take on that role under a formal appointment.
Rooflights or a roof lantern?
It depends on the roof, the light you want and how the room will be used. Our Advice Hub has a full comparison, and we talk it through on site because the choice affects the roof structure as well as the look.
Further reading before you start.
10 things that can increase the cost of a London house extension
A practical guide from the Bayocorp Advice Hub.
Read the guide →Rooflights vs roof lanterns for an extension
A practical guide from the Bayocorp Advice Hub.
Read the guide →Underfloor heating or radiators?
A practical guide from the Bayocorp Advice Hub.
Read the guide →Building Regulations for structural alterations
A practical guide from the Bayocorp Advice Hub.
Read the guide →Other work this often goes with.
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Kitchen refurbishment and installation in North London.
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Contractor-side quantity surveying and estimating in London.
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Send the details, a few photos or a floor plan, and we will tell you what the work involves and the right next step.
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Bayocorp, Flat 22 Eddison Court, 253 Sussex Way, London N19 4DW · 02039 10 00 01 · info@bayocorp.uk · Federation of Master Builders member