Costs per square metre (2017)

We asked our community of architects and design professionals for their experience of domestic projects and how they estimate new jobs. For South East England (where costs are highest), we found the following to be a very rough average. Costs can vary greatly across the country, but if you are outside the South East area, the estimates could be a fair bit less

  • Refurbishment cost: £700-1000 m² 

  • Loft conversion cost: £1,500-2,000 

The ranges above vary significantly, as it is so dependant on the design and level of finish. Extensions in particular can be very difficult to estimate, so you may find this more detailed breakdown below helpful:

 

New build / extension costs:

  • Typical house-builder extension – <£2000 m² (no purpose made joinery, standard window sizes, standard bathroom suites etc)

  • Medium-high architect designed extension – £2600 m² (nice cladding, large expanses of glass, interesting bathroom / kitchen design)

  • Ultra high end extension £3000m² + (central London SW1 – basement construction, high end materials, oak, marble, german kitchens etc)

 

These figures are a very basic starting point and you should not base your expectations for your project on these alone. Speak to an architect about your specific property and design ideas to get a better understanding.

Here’s some sage advice on predicting costs from Suzanne and Kira, two of the architects below:

Suzanne: It is very hard to calculate cost per sq. m as it tends to confuse people. Most clients would make a mistake of only working with size of new extension and forget that entire ground floor is being effected by renovation. This is a huge miscalculation because they will often work with lets say 30 sq m instead of 75 for example. 

Kira: I’d strongly advise homeowners to include a contingency fund of at least 15% of the construction budget. It can be hard to predict what will be discovered in the existing property, once the demolition work has started. With a contingency sum in place, the client is able to mange risks more effectively.

 

Renovation and extensions – case studies

As the number of variables for house renovation projects are so great, we have asked some architects on Design for Me to share some recent case studies with us. This may well be more helpful than a basic cost per square metre, as you can see how these projects compare to your own renovation and extension plans.

 

Case study 1: Ground floor renovation and extension in London, SE9

Project by Suzanne – See her profile here and shortlist her for your project.

extension project costs

Project description

Rear extension to Georgian terrace to create large open plan family space that would include modern kitchen with island and breakfast bar, dining space, living room space with extra storage for children, ground floor WC with shower and utility room.

Project size

Addition to existing ground floor was 5.5m x 5.5m overall and ground floor area being refurbished was 60 square metres.

Construction costs

Cost of ‘second fix’ items (including new kitchen, appliances, worktops, bathroom fittings & fixtures, tiles, lighting etc. £49,951 exc. VAT. 
Cost of works from contractor: £82,020 excl. VAT
Cost of large aluminium bi-fold doors: £7,150 excl. VAT
Cost of wet underfloor heating for entire ground floor: £1,400 excl VAT
Cost of architectural fees: £17,600 inc. VAT,
Cost of contract administration and construction observation for 16 weeks: £4,500 inc. VAT
Cost of structural engineer: £1,250 inc. VAT
Cost of party wall surveyors for three properties: £5,252 inc VAT
Cost of building control: £900 inc. VAT
Cost of Thames water agreement: £1,125 inc. VAT

Level of finish

Medium

 

 

Case study 2: Rear extension, double storey side extension and loft conversion in Bromley

Project by Kira – See her profile here and shortlist her for your project.

extension costs

Project description

Demolition of the attached garage and kitchen extension with addition of two-storey side extension, single-storey rear extension and loft conversion to provide master bedroom with en-suite bathroom.
The project is located in the borough of Bromley. The existing property is 1930s detached house with attached garage (about 1950s) and very poorly planned kitchen extension. Client’s brief asked for open plan kitchen-diner, clever in-build storage solution, additional en-suite on the first floor and loft conversion to provide large master bedroom with en-suite bathroom and walk-in wardrobe.
The clients were keen on high quality modern glazing, costs for which formed a large chunk of their budget.

Project size

260 square metres (100 sq m – new build; 160 sq m – refurbished)

Construction costs

£250,000 (excl. VAT)

Level of finish

Medium – High

 

With this particular project, there was a very creative money saving solution. Although the construction cost remained the same, it freed up month-to-month cash flow for the clients, enabling them to do more. Due to the extensive construction works, the family of four would have had to move out and rent elsewhere for few months. The rent budget would have been lost without any gain. I suggested the design of a garden outbuilding where the family could reside during the construction (under temporary ‘change of use’ rules) and at the later date the outbuilding could be used as an office, gym or hobby room. Modular design made sure the space would be very flexible for the later variety of uses. My clients followed the advice and felt that they gained an amazing asset (which they would be planning in the future anyway), increased the value of their property and had an advantage of over-viewing the construction process 24/7.

extension costs

 

 

Case study 3: Extension and refurbishment in Bristol

Project by Stephen – See his profile here and shortlist him for your project.

 

Extension costs per square metre

Extension costs per square metre

Extension costs per square metre

Project description

Contemporary extension and refurbishment of an ‘Arts and Crafts’ 1920s house. Works include: top floor roof extension to create fifth double bedroom, rear two-storey extension with corner to corner glazing, removal of load bearing walls to create open plan living, new kitchen and two new bathrooms. External works include new raised terrace and new rear terrace with retaining wall. Project works to commence Q1 2018.

Project size

Existing: 241sqm GIA
Proposed: 271.7sqm GIA
Proposed External Works: 43sqm GEA

Construction costs

£295,000 incl VAT

Level of finish

Medium to high finish with large areas of tiling in kitchen and bathrooms, standard kitchen carcasses with purpose made worktops and joinery elements to create unique kitchen
New electrics, lighting and decoration to refurbished areas.

 

 

Case study 4: Refurbishment and extensions in Henley

Project by James – See his profile here and shortlist him for your project

extension costs

extension costs

extension costs

extension costs

extension costs

extension costs

 

Project description

James worked for a family in South Oxfordshire to update and renovate their existing house, with new extensions and a total whole house refurbishment.

The project was to provide a new contemporary external feel to the house, as well as creating new open plan living spaces.

The house was completely renovated and stripped back to bear brick with new ground floors with under floor heating throughout, new electrics, feature lighting and contemporary doors/skirtings etc. To the first floor the roof was partially re-built to improve the energy efficiency of the house and new bathrooms and en-suites were designed to offer contemporary living.

The costs for the works were high due to the use of high finishes, however the simplicity of the finishes provided for great value. We also worked hard with the client to seek very competitive prices for the fixtures and fittings so helping to keep the costs under control. The high level of design and finish meant that the overall project was very good value for the clients.

Project size (floor area)

Total = 280 m2 (3,000 sqft)

Construction cost

£330,000 inc VAT

Level of finish

High

 

 

Case study 5: Park Crescent, Oxfordshire

Project by Allister – See his profile here and shortlist him for your project

rear extension costs

rear extension costs

Interior of Park Crescent is by Adam Carter/Real Homes | Exterior of Park Crescent is by Martin Bennett Photography

Project description

Extension and re-planning of a late Victorian suburban house. Work involved re-planning the rear of the property including replacing a poorly designed 1970s extension with a much larger one and repositioning the kitchen within to create a modern family space that addressed the garden. The floor in the hallway was dropped to heighten the drama when entering the space. Externally the extent and proportions of the new space is framed with metal cladding. It is an unashamedly modern approach that exploits the Victorian grandeur of the house. Clerestory and vertical slot windows also help capture late winter sun as well as providing glimpsed views of the garden from the new entrance porch.

Project size

93m2 of the £150k part of the project Allister was involved with. Of this figure 29m2 was new build.

Construction costs

The internal alterations associated with the extension and the extension itself were in the region of £150,000 ex. VAT. The client spent approximately £550,000 ex.VAT in total with the rest of refurbishment of the property.

 

 

Case study 6: Whole house refurb and new extensions in Bucks.

Project by James – See his profile here and shortlist him for your project

extension costs

extension costs

extension costs

Project description

Whole house refurbishment project and new extensions.To be completed Sept 2017.

Project size

Total = 280 m2 – 3,000 sqft

Construction costs

£295,000 inc VAT (roughly £212,000 excl. VAT)

= approx £757 per square metre

Level of finish

Medium/High

 

 

Controlling your budget

Getting professional advice is the best way to manage your budget. A good architect will work with you to make sure you are spending your budget in the right way and advise where costs would be unnecessary or could be minimised. For larger or more ambitious extensions, you may benefit from using a quantity surveyor too.

Make sure you get three to five quotes from recommended builders (your architect can help compile a tender list for you) to get a firm idea of the costs before starting work.

 

What is ‘Design for Me’?

Design for Me is a free platform to help you quickly find the right design professional for your home project. As a residential architect myself, I started Design for Me after finding that talented and innovative small firms and individuals, who are perfectly placed to design new homes, extensions and/or renovations, can often get buried under the online profiles of large commercial companies.

Before Design for Me, the right architect was very difficult to find!

Once you register your project, we’ll match it with 100s of top architects or architectural technicians, and you can see who may be available and eager to work on your project straight away.

Emily  Design for Me

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