Single Storey Extensions

A single story extension is typically the best way to add value to your property.

There are two types of single storey extensions:

Rear Extension

The rise of the kitchen at the heart of the house creates a very liveable home and a kitchen/dining/living space is easy to create with a rear extension. Up to 8 metres (for a detached house)/6 meters (for a semi-detached/terraced house) from the original rear of the property can be typically achieved via Permitted Development. However, larger single-storey rear extensions are subject to the Neighbour Consultation Scheme.

Side Extension

Side extensions are good for creating secondary type rooms – maybe a utility, a study or if you have the space a bedroom. Side extensions can be built up to half the width of your house.

For an average single storey extension of 20 square metres, the build cost would be from £30,000 for basic quality build costs

How much does a single storey extension cost?

Build Costs

A good place to start is to work out how big the extension will be. This is the main governing factor of the cost of an extension – typically if you worked out a square meter at £1500, that’s a good base price for basic quality build costs.

For an average single storey extension of 20 square metres, the build cost would be from £30,000 for basic quality build costs

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Interior Fit-Out Costs

  • Kitchen
    Budget from £7,000 to £15,000 – the biggest cost factor is the appliances – the better the appliances, the higher the cost

  • Bathroom
    Budget around £5,000 assuming you can connect to existing pipework

  • Utility Room
    Budget from £1,500 to £11,000 depending on size and quality of appliances

  • New Boiler
    Budget from £2,000 to £3,000 depending if the boiler is being fitted in an existing or new location

  • Flooring
    Budget from £25 to £100 per square metre

  • Wall and Ceiling Finishes
    Budget around £85 per square metre for plaster or dry-lining plus paint

  • Bi-fold or Sliding Doors
    Budget from £1,500 to £2,000 per linear metre

Additional Costs

  • Professional Fees (builders, architects, tradesmen)
    An extension of 20 square metres at a build cost of £30,000 could potentially attract professional fees from £12,000
  • Permission Fees (planning permission £206 /permitted development £103)
  • Other (insurance, shared drains/walls, building regulations approval or specific environmental/ecological reports for your property)
    All together, it’s worth setting aside at least £2,000 to cover any fees for permissions and sign off

A single storey extension of 20 square metres of basic quality, will cost a minimum of £44,000 including most fees, but excluding interior fit-out costs.

To calculate the cost of your extension, Yoop Architects take a measured survey of your property, which captures all the information. Then we draw it all up in 3D and create sketches to show sometimes five or six options if it’s not entirely clear how you want to achieve your brief.

A lot of the times there are different ways of achieving your desired result and the more you work with the building, the cheaper, easier and faster your build will be. Once you’ve got a favorite scheme or a couple of favorite schemes, we have a phase called ‘Meet the Builders’. That’s when we can introduce you to a couple of builders, they visit the property and they give you a ballpark figure.


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