Home & Garden cost guide

House Extension Costs

How much will an extension to your house cost?

An extension to your house can be a easier option to moving for gaining more living space, but how much will it cost for types of extension of different sizes?

As a rough idea you can typically say that it will cost between £1,600 – £3,000 excl VAT per m2 including basic plumbing and electrical work (although we’ve have seen higher and lower prices depending on circumstances of the build). This price is per unit area of internal floor space and so a 5x4m single floor extension will have a total floor area of 20m2 and a double storey will have 40m2.

The price for a home extension depends on several factors

  • Where you are in the country
  • How busy the appropriate trades are
  • Are there any building requirements like using a specific type of brick or stone?
  • Are special foundations required?
  • How much work you will do on the project
  • Does it include electrical/plumbing work?
  • Does it include a fitted kitchen?
  • Does it include a new bathroom, shower room or WC?
  • Finish: Tiled floors, walls, render all extra.
  • Flat roof or pitched roof.

As an example the final cost of the project could comprise of

  • Plannings costs – £1,500-£5,000
  • Shell build costs – £1000 – £1,800 per m2
  • Fixtures and fittings – £600 – £1,200 per m2 
  • Decoration finishing – £40-60 per m2

The fixtures and fittings aren’t just electrical and plumbing work but all the plastering and floor work. The shell build includes the windows and external doors plus roof.

A general process for getting an extension built might be

  1. Sketch out some plans/ideas yourself.
  2. Approach an architect and get some detailed drawings made.
  3. Apply for planning permission.
  4. Get some quotes in.
  5. Agree contract with builder. A useful suggestion that some people have done is to break down the payment into different sections based upon completion of job.

This is just a simplified overview, you will also need to get building regulations approval and permission (at least no dispute) from your neighbours as well.

Please try our extension calculator which will estimate the cost of your extension based on external dimensions, roof type and number of storeys.

Below are some prices submitted by WhatPrice? users and personal research. The amount of information submitted varies and what you see is what we get. If you have any of your own prices then please fill out the form at the bottom of the table and help this project.

Single storey extension cost

Typically, a single storey extension will cost more per metre squared than a double storey. In theory a triple storey would cost less still. In practise the difference in cost may be small though. The price per square metre also depends on the size of the property. There are basic costs that don’t increase too much with size and hence the cost per square metre will decrease as the floor area increases.

Total cost of project and m2 costs for having a single floor extension added to your home. The area of the house is usually specified by its internal floor area though sometimes it can be the external area. Also, pay attention in the detailed comments to what was and wasn’t included in the build costs. A simple construction may be just a shell structure (basic plumbing, electrics and building work) whereas many people will specify the actual cost i.e. after you have put in all the fittings (e.g. new kitchen or bathroom/shower suite) furnished and decorated (including carpets or other type of flooring) the extension.

User submitted single storey extension costs

Extension typeRoof typeApprox size (m²)DescriptionPriceUnitsRegionUpdated
Single storeyFlat roof23m²

ground floor 2.650 metres by 8.700 metres goal post shape. 2 room. play room and kitchen knock into existing kitchen to in large. first floor. bedroom. en-suite knock into existing bedroom 4 radiators

(£1,522 per m2)

Total priceEast Midlands2023
Single storeyPitched roof15m²

3m x 5m external size price for basic shell of a pitched roof single storey extension


Per m²East of England2023
Single storeyPitched roof24m²

Single storey extension. Remove existing conservatory and build a 24 sq m extension with pitched roof to house modern kitchen/diner. Included all plastering, decorating, electrics, tiling and kitchen fitting with island.

(£1,733 per m2)

Total priceLondon2023
Single storeyFlat roof56m²

Extension 7000×8000 2 radiators bifold door 5100×2300 pitched roof with 4 velux 780×980 vailant boiler steel supported roof

(£1,714 per m2)

Total priceSouth East2023
Single storeyFlat roof19m²

Single storey (supply and build) included kitchen fit out (labour only)


Per m²South East2023
Single storeyPitched roof15m²

flemish bond single storey extension, basic plumbing and electrics, gas central heating


Per m²East of England2023
Single storeyFlat roof20m²

4m x 5m kitchen / dining area. 4 m of bi-fold doors + under floor heating, full decoration, electrics & plumbing.

(£2,050 per m2)

Total priceSouth East2023
Single storeyFlat roof18m²

Had a rear kitchen extension, 6M x 3M all electrics, & plumbing, plastering, etc, the full Monty, we supplied rads & fittings, included a knock through and some RSJs, extra £350 to have it painted but worth it.


Per m²North West2023
Single storeyPitched roof21m²

Single storey rear l shape extension, lounge extended by 3m, upvc french doors 1900mm with sidelites & top openers, kitchen area by 6m, two windows, part of existing kitchen turned into a shower room, with window, new 4 ft high retaining garden wall, with steps 30 ft long, 25m2 600mm by 600mm slabs for patio area. existing hallway enlarged into old storm porch area. New 2.4m by 1.0m front brick porch, with door and sidelites. two side entry timber gates, concrete marley roof tiles, kitchen and shower room fitting & tiling included, new valiant 32kw boiler.

(£1,962 per m2)

Total priceWest Midlands2023
Single storeyPitched roof2m²

Downstairs toilet 1m x 2m with macerator, lean to roof, toilet, basin, plumbing, electrics [light/switch], floor tiles, door x 1, small window, paint walls and ceiling, skirting.

(£4,670 per m2)

Total priceEast Midlands2023
Single storeyPitched roof22m²

Single storey side extension. Two rooms with radiators and patio doors and one unity room with washing machine fittings and extractor fan. Plastered throughout, tiled pitched room. Very good job. 22m2

(£1,068 per m2)

Total priceNorth West2023
Single storeyFlat roof36m²

6m x 6m kitchen dining extension in block work with flat roof, french doors and one window. Fit one radiator, plaster ready for decorating. Fit kitchen supplied.

(£1,861 per m2)

Total priceLondon2023
Single storeyPitched roof14m²

Single storey to rear of house, extension to kitchen knock down outside wall fit rsj. Extension bedroom, en suite very small. Side of building small utility room. Block and brick, no elec or central heating supplied by builder.

(£4,429 per m2)

Total priceSouth East2023
Single storeyFlat roof15m²

An average rear/side extension measures around 3X5 sq metres. All materials and labour. The walls are all insulated, radiators supplied and fitted, plumbing and electrical is done by certifieds. Boiler, kitchen units, appliances not included.

(£2,507 per m2)

Total priceLondon2023

Double storey extension cost

These are the prices we have received for the total cost either per metre squared or for the whole job of building a double storey extension onto your property. The total area of the job in square metres is the sum of the area of both the lower and upper floor. Usually it is considered to be the internal floor area rather than the external one. Obviously the price can vary considerably depending on the level of finish varying from a basic build which may just be for a shell to a complete finish including kitchen and bathroom fittings as an example. In general it is found that double storey extensions work out to be cheaper than single storey ones in terms of m2 costs – again depending on the level of finish.

User submitted double storey extension costs

Extension typeRoof typeApprox size (m²)DescriptionPriceUnitsRegionUpdated
Double storeyPitched roof40m²

double storey extension approx 40 square metres. bedroom upstairs with en-suite, and 3 rooms downstairs including wc.


Per m²East of England2023
Double storeyPitched roof11m²

Two storey domestic side /rear extension. Utility/laundry wc at ground floor and family bathroom at first floor. Internal size 2.2x5m with traditional cavity wall and pitched roof over. Including tiling to both rooms ,lighting and bathroom fittings

(£3,545 per m2)

Total priceWest Midlands2023
Double storeyPitched roof40m²

Double storey side extension (8m x 5m) plus loft conversion. 3 bathrooms which 2 of were wet rooms. Full new rewire/central heating system, underfloor heating, new kitchen supplied and fitted, house also rendered to complete finish.

(£3,050 per m2)

Total priceWest Midlands2023
Double storeyFlat roof32m²

demolish old extension build new two storey extension raising first floor level and raising second floor roof & ceilings to suit existing building floor area 32m2


Per m²North East2023
Double storeyPitched roof54m²

6.6m x 4.1m, downstairs toilet/shower room , small utility, large dining room, upstairs bedrooms, knock through upstairs to continue hallway, plaster-boarded, plaster finish, all electrics, plumbing included, chipboard flooring to first floor, pitched roof with gable.

(£1,315 per m2)

Total priceCymru Wales2023
Double storeyPitched roof48m²

88,500 including VAT to build 10 by 4.8 metres double story extension. This does not include any bathroom or kitchen fittings. This absolute basic. Expected to add another 35k for ground floor kitchen and upstairs bathroom at least

(£1,844 per m2)

Total priceNorth West2023
Double storeyFlat roof52m²

Including Foundations, Walls, windows, roof, plastering, 26m2 per level

(£1,250 per m2)

Total priceCymru Wales2023
Double storeyPitched roof48m²

48m2 double storey extension complete

(£2,188 per m2)

Total priceSouth East2023
Double storeyPitched roof61m²

New porch plus two storey extension to a semi-detached ex council house, comprising one lounge/diner, two bedrooms and an en-suite. Two standard doorway size external wall knock-throughs were required. 1.2m foundations. Pitched roof + gable end. External dimensions of extension: 4.5m x 6.8m. External dimensions of porch: 2.4m x 1.5m. Price included demolition of existing single storey extension, five external windows, one standard external door, a large set of patio doors. All electrical, plumbing, carpentry, plastering and tiling work included. Price also includes all planning and building regulation costs, which we sorted out ourselves (approximately £2500). Painting, carpets, furnishings etc. are not included. Our builder saved money by re-using materials where possible. There was also no VAT to pay, because his turnover falls below the VAT threshold (we paid for all materials and other trades directly).

(£946 per m2)

Total priceSouth West2023
Double storeyPitched roof30m²

Complete job side extension double storey plus porch and rear extension 5 x 3m full plaster electrics rads in each off rooms standard basic stuff.

(£1,700 per m2)

Total priceNorth East2023
Double storeyPitched roof44m²

Two storey extension, 22m2 per floor Ground floor – lounge two windows north & west elevation, double patio doors to south leading into garden. Fire place on east side of room for wood / duel fuel burner (connecting to existing fire place & chimney from room next door). First Floor – master bedroom with en suite shower, creating corridor from existing building. Relocate existing en suite to master bedroom. Quotes include first fit and second fit & making good.

(£1,409 per m2)

Total priceSouth West2023
Double storeyPitched roof91m²

5mtr sq double storey extension, single storey utility room, cloakroom and kitchen plus front porch. In all 91sq metre project build. Include all internal modifications, electrics and plumbing. All walls painted to top coat.

(£1,462 per m2)

Total priceWest Midlands2023
Double storeyPitched roof43m²

43 square metre extension bathroom utility wet room porch kitchen new heating plumbing electrics warm flat roof gravel dashed landscaping fencing painting outside of house finished project

(£1,342 per m2)

Total priceSouth West2023

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