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What will it cost to build?

Estimating build costs is always one of the first questions we are asked. It is also a very difficult question to answer as there are many factors that need to be considered, such as the size of the project, the materials used and client’s desired specification. This article puts together some indicative costs based on our previous experience, to try and give some understanding of what you might expect.

House extension costs

We estimate approximately £2,500 – £3,750 per square metre

The above figure is representative of a well designed and executed single storey extension in the South East area. The range represents the difference in finish from a standard to high end. A Victorian terrace ‘Side Return’ extension would be considerably higher because of the additional complexities involved in the build.

Modern rear renovation frameless rooflight kitchen design
Listed oxfordshire farmhouse extension

Internal alterations and modifications

We estimate approximately £800 – £1,200 per square metre

Invariably extension projects tend to creep back into the rest of the house and as such if you are intending to remodel and alter the rest of the house, it is prudent to also budget a square meterage cost for any further work that may be required.

Modern family home renovation architects bucks

Kitchen extension

Extending a kitchen can cost anywhere between £15,000 and upwards of £80,000

The actual kitchen tends to be viewed as a separate break out item when it comes to costing because the cost can vary so considerably. The choice between a Swedish flat packed kitchen and a hand made English kitchen designed to fill the same space can impact the final Project cost considerably.

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Luxury kitchen rear renovation design

Loft Conversion

Loft conversions can cost anywhere between £50,000 and £120,000

A budget loft conversion company can produce a dormer loft conversion for between £40,000 and £50,000. Depending on your final specification, a HollandGreen designed loft extension tends to range between £50,000 for a classic dormer to £120,000 for a large glazed ‘L-Shaped’ dormer with multiple rooms.

Light filled family home architecture

Basement Conversion

Providing there is adequate headroom, turning an existing cellar into extra living space would cost around the same as for a simple loft conversion, at around £1000 – £1,350/m².  It is only when you have to start lowering the floor level to increase headroom, involving digging out the ground beneath the house and underpinning the foundations, that the work starts to get expensive at £2000 – £4,000/m².

For indicative costs of a basement conversion:

  • Conversion of existing cellar – £1,150 – £1,450/m²
  • Lowering floor level and underpinning in existing cellar – £1,500 – £2,000/m²
  • Digging new basement space and underpinning – £2,000 – £3,000/m²
  • Digging new basement space beneath the garden – £1,750 – £2,250/m²
  • Creating a lightwell/external access – £5,500 – £9,500 each
  • Engineers fees – £1,000 – £1,500
  • Planning application (where required) – £172
  • Building Regulations application – £750 upwards according to value of works
  • Party Wall surveys (where required) – £700 per neighbour
  • VAT – 20% (added to the cost of all work by a VAT-registered contractor and all fees by VAT-registered consultant)


Additional factors that can add costs when converting your basement:

  • You may need to divert drains currently situated beneath your house
  • Your home may have solid concrete rather than timber subfloors
  • Your home may sit on difficult ground conditions such as clay, made-up ground, sand or marsh
  • The local water table may be high, necessitating constant pumping
  • Access to the site may be difficult which can result in additional costs
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New build home sunken basement luxury games room