how to price a House Extension -
costs estimator to help you
Helping you to understand the costs of your house extension |

This is a general guide to assist you understanding how much your home extension my cost.
No two extensions are ever the same, so many variables are involved but this will help you consider what is involved.
We work with clients and our suppliers to keep costs to a minimum without impacting on the quality of our work.
A basic 4m x 4m (single) story extension
A common estimation of £1,000 - £1,300 per m2 will allow you to gauge an approximation for building work on your home.
These estimations include All Materials, Expenses and Trade expenses to get the property finished to a state where all Walls are Plastered and all Fixtures and Fittings are in place.
Your 4mx4m extension can be build from £16,000
+ Add on 10-15% for other professional fees of your Architect, Planning Application, Building Regulations, Structural Engineer)
+ VAT 20%
Single story extension = £20,600
No two extensions are ever the same, so many variables are involved but this will help you consider what is involved.
We work with clients and our suppliers to keep costs to a minimum without impacting on the quality of our work.
A basic 4m x 4m (single) story extension
A common estimation of £1,000 - £1,300 per m2 will allow you to gauge an approximation for building work on your home.
These estimations include All Materials, Expenses and Trade expenses to get the property finished to a state where all Walls are Plastered and all Fixtures and Fittings are in place.
Your 4mx4m extension can be build from £16,000
+ Add on 10-15% for other professional fees of your Architect, Planning Application, Building Regulations, Structural Engineer)
+ VAT 20%
Single story extension = £20,600
What about if you are considering a double story extension?
As a rule of thumb you can add 50% extra to the build cost of a single story extension.
So, £16,000 +50% = £24,000
+ Add on 10-15% for professional fees (architect, planning application, building regs, structural engineer)
+ VAT 20%
Double Story Extension = £31,200
As a rule of thumb you can add 50% extra to the build cost of a single story extension.
So, £16,000 +50% = £24,000
+ Add on 10-15% for professional fees (architect, planning application, building regs, structural engineer)
+ VAT 20%
Double Story Extension = £31,200
These estimations are for a very nice but relatively straight forward extension to your 'soon to be warm' home. As soon as you start adding additions such as Velux windows, large sliding rear doors leading to your garden with modern (non-standard) radiators you will notice this price going up.
If you plan on including a Bathroom or Kitchen:
+ Add £4,000 for a bathroom again depending on finish that you are looking for.
+ Add £6-10,000+ for a kitchen, again depends on finish you are going for. £6,000 will get you a mid-range kitchen with appliances.
If you plan on including a Bathroom or Kitchen:
+ Add £4,000 for a bathroom again depending on finish that you are looking for.
+ Add £6-10,000+ for a kitchen, again depends on finish you are going for. £6,000 will get you a mid-range kitchen with appliances.
Finishes & Fittings
Above costs assume modest finishes, fittings, electrics and lighting.
+ Decoration costs are in addition to these figures
Above costs assume modest finishes, fittings, electrics and lighting.
+ Decoration costs are in addition to these figures
- Painted/Wall-papered walls
- Carpet floors or Wood Floors all need to be included
Are there any complex site constraints?
Your builder will need to include additional costs in their quotation if any of the following apply:
+ Your soil type and ground conditions may present more costly construction methods / techniques.
+ Limited access to the site. Will it be easy for the builder to bring in tools and machinery easily?
+ Existing structure. Are you removing any structural walls? If so there will likely be additional costs for steelwork.
+ Are you moving any pipework, drainage, gas meters?
Your builder will need to include additional costs in their quotation if any of the following apply:
+ Your soil type and ground conditions may present more costly construction methods / techniques.
+ Limited access to the site. Will it be easy for the builder to bring in tools and machinery easily?
+ Existing structure. Are you removing any structural walls? If so there will likely be additional costs for steelwork.
+ Are you moving any pipework, drainage, gas meters?
Location
+ As already mentioned above, in the South East you can expect to pay more than the rest of the UK, and notably more in London.
Materials and construction techniques
+ Consider the type/quality of construction materials involved and the type of construction.
+ As already mentioned above, in the South East you can expect to pay more than the rest of the UK, and notably more in London.
Materials and construction techniques
+ Consider the type/quality of construction materials involved and the type of construction.
Managing or reducing your project costs
- It pays to get professional advice from a good architect ask friends/neighbors if they know of anyone who assisted them. They could help you realise obstacles they came up against.
- When in touch with a good builder speak to them to ask for their opinion/advice where costs could be saved/better spent but be very careful they know all works will have to be signed off by building control.
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And finally, NEVER pay-out to much money in stage payments, always retain some money until after all works and snagging lists are complete and you are completely happy. Looking for a great architect view a great selection of professionals at Local Architects Direct |