Budget Extensions

Detailed Extension Budget Estimate

When you are satisfied that you have explored as many aspects of your house extension design ideas as you can, and established some reasonably acceptable price parameters for your new build home improvements, contact Simply Build Extensions for a free set of detailed budget prices. 

These are indicative quotations are provided to help you make your final building design and specification choices.


Considering Detailed Extension Budget Costs

Individually taken off and prepared specifically for your extension or conversion project, they are available entirely without obligation. They set out a series of alternative building envelope make ups and give suggestions for a number of additional material supplies and on site works, like roofing, windows, external cladding, stairs and so on..

Typical House Extension Building Costs in 2010

Costs of Planning           £ 5,132     Range£1K    - £27K   

Ground floor extension   £21.123    Range £12K - £30K   Cost /m2   £500 - £1,560

Extension on two floors   £43,970    Range £30K - £115K  Cost /m2  £500 - £1,500

                                                                                                                  Source “What Price”

Why the Spread of Costs?

Builders quotations for a 60m2 house extension will be different if this is all on the ground floor, or spread over two (30m2 per floor) or even three floors (20m2 per floor).


Foundation & Roof Costs

Firstly, this is because the size of the foundations and roof for any building extension will change as the size of each floor gets smaller. Also different ground conditions may need different foundations depending on the height and weight of the rooms in the extended space

Additionally, planning requirements can determine the height & type of roof extension, as well as its covering.  All vary the quantities and prices of materials needed for the project.


House Extension Foundation Costs

House Extension Foundations


Design & Specification Costs (Unintended?)

Then there are things like shape complications, window and roof types, and levels of insulation required, to consider. The fact that, for example,, the price for a very basic uPVC window possibly quintupling for a triple glazed, split frame, high eco specification of the same size illustrates this point,

Crane Lifts House Extension Roof

Cost of Craning in House Roof


Access & Space Costs

Additionally things like how easy the site is to access, how much room there is to work around the building and store materials, what the new extension has to connect into, and how, can make a difference. 


House Race Limited Acces Space

Restricted Access & Space
ITV Houose Race
Bull Ring







Prices for Electrical, Plumbing, Heating & Utility Installations

These are often fairly ‘big ticket’ building costs, relating to the price of each item, like plugs, dimmer switches, boiler, radiator, bath/shower suite, kitchen fit out, etc.

The basic price for building the room space may not vary too much, but the more space you can spread these individual high cost items over, the less the price of building each metre square, or foot square, building becomes.


Small Room –v- Large Room Extension Costs

You can apply the same broad principle to the size and shape of the new rooms you need to give you the extra space, usability, and comfort the improvements to your home are intended to bring.

Within limits, the less walls, corners, complications and so on. The limits are:-

a)     the extent of the clear spans between supporting walls over which floors or roofs have to go. If these are very wide then special structural materials and designs may be needed at extra cost.

b)    the width, height, and extent of door and window openings. As in (a) if these are very large, then special structural design provisions may increase extension costs. 


Small -v- Large Hoouse Extension Costs
























Further Influences on Building Prices

As outlined, you can expect costs for a ground floor extension to be more per square meter (or square foot) of floor area than costs for a two storey extension with the same ground footprint.  Adding a third floor, particularly by using part of the roof space, may reduce this even more.

Extending Upwards - Penthouse Flat

Extending Upwards - Penthouse Flat

  Building prices will also be influenced by:-

  • Location. As with other things building costs vary throughout the UK
  • Order Books. If trades are not very busy you might get better prices, but if people have left the industry then then those that remain may be busier.
  • Design & Planning Conditions. Brick & tile prices, for instance, can vary by 200% to 300%
  • Own Labour, i.e. the amount of work you can do yourself.
  • Fittings – quality and manufacturer can make huge differences.  Kitchen costs, for example, can be anything between £7,000 and £45,000 for more or less the same provisions, but from different sources.
  • Joinery. In the same way the costs for your stairs, floors, doors, wardrobes, and so on in your extension could vary by 300% or more. 

Costs of Building and Extensions

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