An extension planned around the existing home

Rear, side-return and wraparound extensions

The build can bring together foundations, structure, walls, roofing, openings and the connection to the existing house. The design has to resolve levels, drainage, glazing and how the new space meets the old.

Tell us whether the kitchen, utility room or bathroom will move. A new room still needs practical routes for services, deliveries and everyday use.

Malvern Mews during construction, with herringbone brickwork, dark cladding, scaffolding and a boarded entrance — Malvern Mews during construction. Our director’s previous project-management experience, before Vayton.

Shell construction or a finished space

Decide whether you want a structural shell, a weather-tight envelope or a completed interior. Windows, doors, rooflights, kitchen fitting, heating, electrical work, plastering and decoration should each have a clear supply and installation responsibility.

A shell price and a finished-extension price are not directly comparable. We set out the intended handover condition so you can see which work is included and which remains.

What needs to be ready before construction?

Planning permission, permitted-development conditions and building regulations are separate considerations. Most extensions need building regulations approval, and the planning route depends on the design and property. The appropriate advisers should review structural information, drainage requirements and any party-wall matters.

Before final pricing, agree the drawing revision, structural details, key selections and access arrangements. Ground conditions, existing foundations and hidden services can affect the work. Where something cannot yet be confirmed, the quotation should state the assumption or provisional allowance and how it will be resolved.

What affects house extension costs?

For typical London prices by extension type, VAT and a worked budget, see house extension cost in London.

Area is a useful starting point, but a price per square metre does not capture every interface with the existing building or the chosen interior.

For broad UK context, a single-storey extension typically costs £1,800–£3,000 per m². This is a typical market figure, checked on 28 October 2026, not a Vayton rate or a London quotation. Confirm the inclusions and tax basis before using it.

An extension budget also has to cover the chosen kitchen or bathroom, glazing, changes to the original house, professional fees and any work excluded from the building package. Compare quotations against the same drawings and finish schedule.

Quotation item	What to make clear
Ground and structure	Foundations, excavation access, drainage changes, steelwork and existing-building alterations.
Building envelope	Wall and roof construction, insulation, glazing, external doors and rooflights.
Internal fit-out	Kitchen or bathroom scope, heating, electrical work, plastering, flooring and decoration.
Access and project costs	Protection, temporary arrangements, waste, professional fees and approval fees where included.

The written quotation identifies inclusions, exclusions, supply responsibilities and any provisional items. Confirm VAT treatment and payment stages for the agreed package.

Compare quotation scopes

What small-extension quotation examples actually cover

Small additions often sit inside a larger refurbishment or conversion. Their schedule allocations are useful evidence of scope, but shared costs mean they are not standalone extension offers.

Historical quotation	Price including VAT	What the figure describes
Rear bathroom formation · June 2026	£12,600 (£10,500 plus £2,100 VAT)	Approximately 8 m² of new bathroom formation: joist floor, one external wall build-up, roof covering, insulated lining and agreed fit-out/plumbing. An item within a larger refurbishment, not a complete independently priced extension.
Garage conversion with compact side WC extension · July 2026	£38,940 (£32,450 plus £6,490 VAT)	The entire coordinated conversion, room reconfiguration, standard kitchen, canted bay and approximately 1.26 m² WC extension package. The quote assumed straightforward foundations/drainage and retention of a sound garage roof.

These are dated quotation examples from our director’s earlier business. They are not completed Vayton projects or current offers. Client names and addresses are omitted.

The July package carried an indicative seven-to-nine-working-week programme after approvals and design release. That duration belongs to the stated combined scope. It is not a promise for a rear, wraparound or double-storey extension.

For a new rear, side-return, wraparound or double-storey project, get a design-specific quotation covering foundations, structural openings, roof, glazing, services and finishes. We have not converted these small additions into generic type-by-type rates.

Explore garage conversions · See the wider refurbishment examples

Planning permission, permitted development and party walls

Some house extensions can proceed under permitted development, provided the proposal meets every relevant condition and the property has those rights. Other designs need planning permission. Flats do not have the same householder rights. Your designer should establish the route for your address before the programme is fixed.

Building regulations and any party-wall procedures are separate from planning. Where work affects a shared wall or involves excavation near a neighbouring building, establish the party-wall position with the appropriate adviser before construction.

Check the householder permitted-development guidance ↗

The government’s party-wall guidance explains when notices or agreements may be needed.

Read the party-wall guidance ↗

How long does a house extension take?

Construction of a standard extension typically takes around three to six months. Design, approvals and the lead-in before site work are additional. Treat that as broad context, because the size, specification, access and work to the existing house determine the programme for your project.

Agree the main stages before starting: site preparation and foundations; structure and roof; windows and weatherproofing; first-fix services; linings and finishes; kitchen or bathroom fitting; and snagging. We also agree when the existing house will be opened up, which facilities will be unavailable and which deliveries control the next stage.

Questions before you start

Can we contact you before planning is approved?

Yes. An early conversation can help define the construction brief. A start date and firm package depend on the design, approvals, scope and availability being ready.

Can we stay at home during the build?

That depends on the separation of the work, access and the facilities affected. Talk to us about the kitchen, bathroom, heating and routes through the house before agreeing the programme.

Can we supply the kitchen or glazing ourselves?

Yes, subject to agreement. Confirm dimensions, specification, delivery dates, storage, installation responsibilities and how delays or product issues will be handled.

What to send for a useful quotation

Send the postcode, proposed and existing plans, planning status, structural information and your preferred timing. Include the intended rooms, key products, site access and whether you want shell construction or a finished interior.

Related work

Structural alterations

Kitchen installation and refurbishment

Patios and external works

Further guidance

Planning Portal: extension permissions and building regulations ↗

Before disturbing existing textured ceilings or concealed materials, resolve the relevant survey information. Read our Artex and asbestos preparation guidance.

House extension builders in London

Tell us about your extension.