The Definitive Guide to:
How much a House Extension costs in 2018


“How much
will a
kitchen
extension
cost me?”


Find out more

     

     

    Introduction

    In this article we give guidance regarding the current cost indications for an extension.

     

    Contents

    1 Rule of Thumb
    2 Cost Indicator
    3 Cost Guide with Case Studies
    4 Conclusion
    5 Contact Us
    6 Glossary as Footnote
    7 Other Viewing

     

    1 as a rule of thumb


    This year you would be looking at about:

     

    London:

    rest of UK:

    £1,550 – £2,100 per m2

    £1,250 – £1,600 per m2

     

     

    2 simple cost indicator

    Average, budget build

    – standard windows & sanitary ware, no special joiner work.
    Cost: under £2,000 m² (London)

    Medium to high end build

    – designed by architects, lots of glass, cladding and nice kitchen & bathrooms.
    Cost: from £2,650 m² (London)

    Top class build

    – luxury materials, incorporation of basement or part basement, German kitchen design.
    Cost: from £3,100 m² (expensive London postcode)

    pricing image for blog on cost of extensions
     
     

    3 your guide to current extension pricing


    PRICE
    SAMPLES

    Some of the prices below are
    bang up to date, as they were
    completed September 2018.

    For the sake of comparison,
    there are one or two examples
    from 2016-17
    [i.e. pre-Brexit for the
    quotation stages].

    See the dates by the examples.


    START PLANNING
    YOUR EXTENSION

     

    example 1 in detail

    Project DESCRIPTION

    extension image for blog on cost of extensionsStylish asymmetrical rear extension in South Croydon.

    This was an exciting project with a new client who wanted a contemporary design. We assigned Seren, one of our creative architectural designers to create some options. One of her designs had a double apex – however we wanted to show consideration to the neighbours – so we went with this asymmetrical alternative. We think it which actually looks better. For explanations of pricing detail, see footnote.

    SIZES

    Existing: 151.7m2 GIA (Gross Internal Area)
    New Work: 21m2 GEA (Gross External Area)
    Proposed: 172.7m2 GIA (Gross Internal Area)

     

    BUILD COST

    £122,300 + VAT
    £128,415 incl. VAT

    FINISH

    Medium to high end

    Single Storey Rear Extension
    and Landscaping,
    South Croydon.

    Date:
    Summer 2018

    Decorated letter T for article on cost of extensions by Extension Architecturegrand total
    £122,300 + VAT

     

    the details

    Decorated letter P for for article on cost of extensions by Extension Architecturepreliminaries  £10K

    Decorated letter S for article on cost of extensions by Extension Architecturescaffolding  £2.5K

    Decorated letter E for article on cost of extensions by Extension Architectureexisting
    house work
      £3K

    Decorated letter S for article on cost of extensions by Extension Architecturesingle storey extension  £46.3K

    Decorated letter E for article on cost of extensions by Extension Architectureexternal doors  £7.25K

    Decorated letter I for article on cost of extensions by Extension Architectureinternal doors  £2K

    Decorated letter E for article on cost of extensions by Extension Architectureexternal windows  £5.5K

    Decorated letter S for article on cost of extensions by Extension Architecturestructural /
    steel work
      £7K

    Decorated letter J for article on cost of extensions by Extension Architecturejoiner work  £5K

    Decorated letter R for article on cost of extensions by Extension Architecturerainwater provision   £2K

    Decorated letter K for article on cost of extensions by Extension Architecturekitchen
    client to supply
      £2.25K

    Decorated letter U for article on cost of extensions by Extension Architectureutility room
    client to supply
      £0.75K

    Decorated letter P for for article on cost of extensions by Extension Architectureplumbing
    1st fix
      £2K

    Decorated letter P for for article on cost of extensions by Extension Architectureplastering   £7K

    Decorated letter F for article on cost of extensions by Extension Architecture

    fire protection £0.5K

    Decorated letter H for blog on glossary by Extension Architectureheating  £7K

    Decorated letter E for article on cost of extensions by Extension Architectureelectrical  £8K

    Decorated letter E for article on cost of extensions by Extension Architectureflooring & wall  £7K

    Decorated letter D for article on cost of extensions by Extension Architecturedecorating  £1.75K

    Decorated letter N for article on cost of extensions by Extension Architecturenegotiation  £-4.5K

     

    note

    This was quite a high-end finish, so the price was a little more than average. The build cost does not include architect fees, but you can contact us for a free quote.


     

    example 2 in brief

    extension image for blog on cost of extensionsRear extension for a new cutting-edge kitchen.

    Project DESCRIPTION

    Our client wanted a single storey rear extension for a new, state-of-the-art kitchen that used the latest developments in kitchen technology.

    SIZES

    Existing: 48.06m2 GIA (Gross Internal Area)
    New Work: 18.57m2 GEA (Gross External Area)
    Proposed: 66.62m2 GIA (Gross Internal Area)

     

    BUILD COST

    £67,510 + VAT
    £81,012 incl VAT

    FINISH

    Medium – high

     

    Single Storey Rear Extension,
    Worcester Park.

    Date:
    2017

    Decorated letter T for article on cost of extensions by Extension Architecturegrand total
    £67,510 + VAT

     

    note

    This was also quite a high-end finish, so the price would be above average. These build costs exclude planning fees, so contact us for a free indication.


     

    example 3 in brief

    extension image for blog on cost of extensionsThis extension features an attractive lightwell courtyard.

    Project DESCRIPTION

    These clients had the intention of extending the flat they owned as a buy-to-let investment. They were about to move to North London but changed their mind when they realised the new design would be very contemporary and appealing. They moved into it themselves.

    SIZES

    Existing: 41.2m2 GIA (Gross Internal Area)
    New Work: 22.6m2 GEA (Gross External Area)
    Proposed: 63.8m2 GIA (Gross Internal Area)

     

    BUILD COST

    £102,148 + VAT
    £122,578 incl VAT

    FINISH

    Medium

     

    Single Storey Rear Extension,
    Tooting Bec.

    Date:
    2017

    Decorated letter T for article on cost of extensions by Extension Architecturegrand total
    £102,148 + VAT

     

    note

    This was a medium to high finish, so the pricing would be slightly above average. These build costs exclude planning fees, so contact us for a free indication.


     

    example 4 in brief

    extension image for blog on cost of extensionsWe also did landscaping to go with this new extension.

    Project DESCRIPTION

    This family were referred by one of our largest clients for their domestic home improvement. They wanted a new extended kitchen with comprehensive landscaping for their garden. They were hoping to have it finished in time for a family wedding so they could host some of the relatives! (Note: it is never really ideal to rush on builds because it may cause compromising on contingency issues which otherwise need more time allocated.)

    SIZES

    Existing: 55.9m2 GIA (Gross Internal Area)
    New Work: 10.4m2 GEA (Gross External Area)
    Proposed: 66.3m2 GIA (Gross Internal Area)

     

    BUILD COST

    £114,816 + VAT
    £137,779 incl VAT

    FINISH

    Medium to high

     

    Single Storey Rear Extension
    and Landscaping, Carshalton.

    Date:
    2016 – 2017

    Decorated letter T for article on cost of extensions by Extension Architecturegrand total
    £114,816 + VAT

     

    note

    This earlier example was also to a good finish, so the pricing would be higher than a budget extension. Also the price includes landscaping, but not architect fees, so contact us for a free indication.

     

    4 conclusion


    As you will have seen, planning for your extension is quite a considerable outlay.

    That said, it is cheaper than moving. Speak to your bank about finance options. The rates for this year are slightly higher than last year, but you will recoup your expenses via additional value in your property. Note also that with high-end finishes or smart home technology, your costs will be above average, albeit a worthwhile investment.

     

    5 contact us

    We hope this guide has given you a good idea of cost forecasts for an extension


    If you would like help to plan your budget, ask us for a free consultation. Call on 0203 409 4215 or fill your details so our planning team can arrange an appointment with you.

    Get in Touch

    6 glossary as footnote

    Here is what is meant by the phases in the pricing example 1, above:


    Preliminaries refers to the early stages of a project; for example the site set-up, insurance, protection, sealing off the site area, and Health & Safety equipment.

    Existing house work is fairly self-explanatory and means any works needed to make good on the host building; which are separate from the new extension.

    Single storey extension is clearly the body of new work, made up of stages such as: installing a suspended timber floor; applying insulation and sound-proofing; using airbricks to ventilate; rendering the exterior; brick-laying; adding cavity board; smooth plaster-skimming; using wall ties; digging for the concrete foundation; co-ordination with window supplier; connecting drainpipes to the manhole and Lead flashing.

    It would also need – for a flat roof – timber, joists, insulation, plasterboard, flashings, aluminium edging, and skimming. For a sloping roof in would entail: tiles & battens, a membrane & rafters, insulation, edging, flashings, a soffit ceiling, plasterboard, and skimming. For a stud wall you would need: timber studs, insulation, a damp control layer, fixings, plasterboard & skimming.

    Doors include your external doors which could be bi-fold doors and a hardwood front door. You could need a few internal doors in different styles.

    Windows would be several items in whichever style(s) you have received planning permission for.

    Steels and structural work are mainly your steel beams, also known as i-beams or RSJs (rolled steel joists). Also needed are lintels, a sleeper (load-bearing) wall, joist-checking; the inclusion of a hollow section and wind posts for the windows.

    Joiner finishes would include: the door mouldings, architraves, skirting, panelling; fixings, handles, shelves & cornicing; curtain rails; hinges, nails & linings

    Your rainwater provision means your downpipe guttering, soffit, flashings, pipe routes, drainage routes and channel to garden. The break-down for your kitchen (and utility room) would be to install the appliances and fit the units, worktops & splashbacks.

    Some phases are pretty self-explanatory; such as plastering which would include the new and existing building, according to need. Thus these examples are indicative as each project would vary according to its condition, size and needs. It is best to get a quote which can be adjusted after a site survey.

    Fire protection would be supplied to your steels, cables, and pipe-work. Heating is also variable as you may be having under-floor heating, regular heaters and / or a new boiler. Your electrics could include new wiring to your kitchen, living room, utility room & garden.

    Flooring and walls could be kitchen & utility room tiles, slabs for your patio & stairs, garden paving, work (if needed) to the neighbour boundary; and a patio boundary wall.

    Decorating and scaffolding are also pretty self-expanatory and the respective quotes would vary according to need and the size of your property.

     

    7 further viewing

    See some other extensions we have built, in our single storey extension portfolio. Please note our portfolio does not include price information, but if you would like an indication based on any of these,
    get in touch
    and we will get back to you with specific guide costs.

     

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