Two-storey extensions, designed, approved and built

Guide from £56,000Learn more

Two-storey rear extensions

A two-storey rear extension is a new two-floor addition built onto the back of your house, usually giving a larger kitchen or living space on the ground floor and one or two bedrooms or a bathroom above.

Two-storey side extensions

A two-storey side extension is a new two-floor addition built into the space beside your house, often over a driveway or side passage.

Guide from £86,000Learn more

Two-storey wraparound extensions

A two-storey wraparound extension is an L-shaped addition that extends both the side and the rear of your house, on two floors.

Guide from £120,500Learn more

Part single, part two-storey extensions

A part single, part two-storey extension is an extension where the ground floor is wider or deeper than the floor above, so only part of it rises to two storeys.

Guide from £72,000Learn more

Extensions over a garage

An extension over a garage is a new first-floor room built on top of an existing attached garage, usually a bedroom, en-suite or study.

Guide from £31,500Learn more

First-floor extensions

A first-floor extension is a new upstairs room built on top of an existing single-storey part of your house, such as a rear kitchen extension, a utility or a side annexe.

Guide from £25,000Learn more

Two-storey front extensions

A two-storey front extension is an addition built forward of the front wall of your house on both floors, often a deeper hall or study below and a larger bedroom above.

Guide from £26,500Learn more

By house type

Guide from £56,000Learn more

Two-storey extensions for semi-detached houses

A two-storey extension for a semi-detached house is a two-floor addition to the rear, the open side, or both, designed around the attached neighbour on one side.

Two-storey extensions for detached houses

A two-storey extension for a detached house is a two-floor addition to the side, rear or both of a house that stands on its own plot.

Guide from £86,000Learn more

Two-storey extensions for end-of-terrace houses

A two-storey extension for an end-of-terrace house is a two-floor addition to the open side or the rear of the last house in a row.

Guide from £86,000Learn more

Rooms and uses

Guide from £56,000 (before kitchen units)Learn more

Kitchen extensions with bedrooms above

A kitchen extension with bedrooms above is a two-storey extension designed so the ground floor becomes a larger, usually open-plan kitchen and dining space, with one or two bedrooms or a bathroom on the first floor.

Extra bedroom and en-suite extensions

An extra bedroom and en-suite extension is a two-storey extension planned around a new double bedroom with its own shower room on the first floor, with a ground-floor room below.

Guide from £56,000 (plus en-suite)Learn more

Two-storey annexe extensions

A two-storey annexe extension is an attached extension laid out as self-contained living space on two floors, usually with a living area and kitchenette below and a bedroom and shower room above, for a relative living with the family.

Guide from £86,000 (plus fittings)Learn more

Garage conversions with a room above

A garage conversion with a room above is a project that turns an attached garage into living space and builds a new room on top, so you gain space on both floors in one build.

Guide from £31,500 (room above only)Learn more

Design and approvals

Two-storey extension plans and drawings

Two-storey extension plans involve a measured survey of your house, design options, and a set of scaled drawings showing the existing and proposed floor plans, elevations, a site plan and a location plan.

Planning permission for two-storey extensions

Getting planning permission for a two-storey extension involves checking whether permitted development applies, preparing drawings and supporting information, submitting a householder application to the council and dealing with questions until a decision is made.

Structural engineering for two-storey extensions

Structural engineering for a two-storey extension involves calculating how the new floors, walls and roof carry their loads down to the ground, and designing the beams, lintels, foundations and ties into the existing house to suit.

Building regulations for two-storey extensions

Building regulations approval for a two-storey extension involves preparing technical drawings and a specification that show how the extension meets the rules on structure, fire safety, insulation, ventilation, electrics and drainage, getting them approved and having the work inspected.

Party wall notices for extensions

A party wall notice is a formal written notice that you must give your neighbours under the Party Wall etc. Act 1996 before certain work on or near a shared wall or boundary in England and Wales.

Design and build two-storey extensions

A design and build project for a two-storey extension involves one team taking responsibility for the whole job: the survey, design, planning or permitted development, structural engineering, building regulations, party wall matters where they apply and the construction itself.

Guide price tool

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Permitted development checker

Answer a few questions about your house and plot to see whether a two-storey extension is likely to need planning permission where you live.

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What happens next

Free site visit
We look at your house, boundaries, access and drains, and talk through what you need.
Design and approval
Measured survey, drawings, then planning permission or a lawful development certificate.
Engineering and fixed price
Structural design and building regulations approval, then a fixed build price in writing.
Build and sign-off
Vetted teams working under S&K build it; we arrange the completion certificate.

How it works in detail

Reviews

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Guides

Straight answers on costs, rules and building work, written for homeowners.

How much does a two-storey extension cost in 2026?

A two-storey extension typically costs £2,000–£2,700 per m² of new floor area in 2026, including VAT, which puts a 28 m² rear extension at about £56,000–£75,500.

Do I need planning permission for a two-storey extension?

Often yes: a two-storey extension needs planning permission unless it meets the strict permitted development limits for your part of the UK, which in all four nations can allow some two-storey rear extensions.

Can I build a two-storey extension under permitted development in England?

Yes, in England a two-storey rear extension to a house can be permitted development if it extends no more than 3 m beyond the rear wall of the original house and stays at least 7 m from the boundary opposite that wall.

What are the rules for two-storey extensions in Wales?

In Wales, a two-storey rear or side extension can be built without planning permission if it meets the Welsh permitted development rules, which differ from England's.

What are the rules for two-storey extensions in Scotland?

In Scotland, a two-storey extension can be permitted development under Class 1B only if no part of it is within 10 m of any boundary, it is no higher than the existing house, it does not front a road, and the house is not a flat or in a conservation area.

What are the rules for two-storey extensions in Northern Ireland?

In Northern Ireland, a two-storey rear extension can be permitted development if it extends no more than 3 m beyond the rear wall of the original house and stays at least 7 m from the boundary opposite.