How Much Does a House Extension Cost?

How much does a house extension cost? It’s almost always once of the first questions that we get asked when attending a homeowner’s property, so we thought it would be a good idea to do a short post on the topic with the aim of trying to answer it.

We’ll break the post down into three sections; the first section will cover the cost for a single storey extension, then we’ll touch on two storey extensions and finally we’ll discuss other costs that need to be factored into your project.

Single Storey Extension

As a general rule of thumb, we’d allow £1,200 per m2 for a standard traditionally built single storey extension. If you opted for a higher end specification then this could increase to around £1,500 per m2.

Bearing in mind the average extension is around 4m x 5m (20m2); this gives a rough build cost of £24,000 (based on a lower specification).

VAT at 20% will add another £4,800 onto the build cost.

Build cost only for a single storey extension: £28,800

What about a two-storey extension?

We’d allow an extra 50% onto the build cost of a single storey extension. At the end of the day, the only difference between a single storey and two storey is some additional brick/block work, some ceiling joists and extra internal doors and windows, along with some stud walls and electrical and plumbing bits.

So, based on a 20m2 two-storey extension at a rate of £1,800 you would be looking at £36,000 for a two-storey build.

Once again, VAT is to be added on: £7,200

Build cost only for a two-storey extension: £43,200

What other costs do you need to factor in?

Professional Fees

The first step in your project would be to get planning and building regulation drawings compiled. Allow £650.00 for a full set of plans for a single-storey extension and £850.00 for a two-storey extension.

You then need to submit a planning application to the local authority. The fee for a domestic household application is £172.00.

A full building regulation application will then need to be submitted. You can either submit it to the local building control office or use an approved inspector. Allow between £450-£520 for their fees.

If you are knocking down a load bearing wall or creating an opening through the rear elevation, then you will require a structural engineer to design and specify structural steels. You’d be looking at £180-300 for this service, dependant upon the number of steels required.


Kitchens and Bathrooms

On top of the build costs we’d factor in a £5,000 sum for a bathroom suite. Obviously, this could be reduced to around £2,500 for a lower specification bathroom or increased significantly if you opted for top shelf sanitary ware and finishes.

Kitchen costs can also vary significantly (we have worked on a project where the kitchen cost in excess of £50,000!) However, if you’re looking for a ballpark figure then we’d allow £10,000 for a medium range kitchen, from say Howden’s.

Fixtures and Fittings

Again, it is difficult to put a price on the cost of internal fixtures and fittings as the prices vary significantly.

Do you want solid oak internal doors or are you happy with cheaper moulded doors? Farrow and Ball or Dulux paint? White plastic faceplates or expensive polished chrome plates? The list goes on….

We’d recommend you sit down and decide upon what kind of specification fixtures and fittings you require, breaking each individual component down.

Anything else?

The cost of building an extension in London compared to Newcastle would be significantly different; therefore, location will be a leading cost factor.

You can attempt to cut costs by opting for different materials. For example, building an extension in block work with a render finish, in lieu of block and brick, would reduce labour and material costs. Likewise, opting for attic roof trusses instead of a traditional two-storey extension would create cost savings, but not compromise on space.

Always allow a 15% contingency sum when planning your budget for unforeseen works. This will ensure you have a buffer should something unexpected crop up during the build.

The first step in your project is to get a good designer on board, who can listen to your requirements before advising on the pros and cons of the different options that are available to you.

If you’re thinking of having an extension and require some further advice, then we offer a free consultation to run through the different options available to you.

Simply drop us an email or give us a call
0191 290 3742

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