Average price guide for Loft and Extensions

PLEASE NOTE : These are estimates prices, free quotation visit is always compulsory

House extensions

A house extension can be the best investment you ever make. An extension can add far more value to your house than you spend on it.

Average Extension Build Costs In £ per m² + VAT
  (Costs for 2016 in London area, other builders)
  Basic Spec Medium Spec High Spec
Single Storey Extensions £1,450 £1,825 £2,500
Double Storey Extensions £1,000 £1,600 £2,200
Basement Extensions £2,000 £3,000 £4,000
Refurbishments £500 £1,250 £2,000
Action Build can offer fixed 5 % discount for every specification until 31 May 2018

In recent years in London area have gone up a bit. The build cost for a simple extension can be £ 1000 - 1500 per square metre OF CREATED FLOOR SPACE. For glass extensions or high spec design allow bigger budget.



The cost of a single storey can vary from £ 1250 per m2 for simple build ans spec, to 2500 for a high spec build. Single storey rear extensions or side return extensions will often included the cost of a new kitchen.



The cost for square metre will be less, because they share the below ground work. The cost can vary from £ 1000 to 2300 per m2 high specification project.


Site Costs

  • Location. The cost of labour will vary across the areas. London is the most expensive, and this could add 5 % to costs. If you can provide parking and welfare this can help reduce it.
  • Type of House. Access to the back of a terraced house is not easy, so there may be some extra labour costs. You can offset this a bit by allowing us to use part of the house for storage and materials.
  • Planning Conditions. If the house is Listed or in a Conservation Area build costs will go up. The best bet here is to work with your architect on a design that meets both Planning and Budget.

Build Costs

  • Extension Size. This will affect the cost more than any other factor. You can think of house extension costs in £ per m², anywhere in the range of £1,000 – £3,000. A small change in size will have a big effect
  • Main Features. If it is a kitchen extension you will need to factor in the cost of the kitchen fittings, which can add quite a bit. The best bet is to look at the level of spec and make sure it works with your budget.

Extra Costs

  • Refurbishment. It makes sense to renovate while the extension is being built. This is great but refurb costs are high compared with build costs, so it’s good to estimate this properly to keep to budget.
  • High Spec Finish. A kitchen can be £10000 or £50000; patio doors can be £5000 or £25000; a floor can be £20 per m² or £200 per m². Choose each of these with care and you will be on the right track. Action Build can fit anything from cheap to expensive, as long as it meeting basic buidling spec standards.
  • Extra Features. Keep in mind that extras like under floor heating, high spec lighting and ceiling speakers can bump up the cost. To stay on budget it’s good to look at these costs in more detail.

Loft Conversion

Depending on the roof structure and planning constraints, a loft conversion is one of the most straightforward ways of getting extra space. Almost all houses can benefit from this extension with a bit of basic planning

A standard room in loft conversion is the cheapest and could start at around £ 10000. This will usually involve: the reinforcement of the floor, a couple of skylights, added insulation, a staircase to the loft , electrics, lighting and heating, fire safety measures to comply with Building Regulations such as fire doors and smoke alarms.

Dormer loft extension, second option which does not require dramatic changes to the roof is to do the above first option and add dormer windows. This will increase the useable floorspace and can be used to add head height which gives you more options when it comes to placement of the stairs. This will cost upwards of £ 20000. However dormer loft conversion with a double bedroom and en suite costs about £ 30 K to 50K.


Loft conversions which involve raising the roof or even changin the roof structure. This options is the most expensive as i require the removal and rebuild of the existing roof. It also requires planning permission approval so your local planning permission aplication is a must. Another added expense will be the additional design work that may be needed as it is more compicated that a room in roof, or dormer loft conversion. This type of work is lekley to cost well in excess of £ 40000.

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"We have been very pleased with Action Build Services’ refurbishment of our kitchen, which included structural and decorating work as well as fitting new kitchen units.  Their workmanship was of a high standard; and they went out of their way to discuss and to resolve inventively the complications which inevitably arise with such things.  Wherever possible they did this within their original, competitive, quotation.  The boss, Michael, kept in close touch with us and with progress on the job, to ensure that all was done to meet our and his expectations; and the team   carrying out the work were professional, friendly and unfailingly helpful."

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