Basement below rear extension - Cost approx?

14 Jul 2016
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United Kingdom

Am just in the process of drawing up some plans to extend my house. The original plan was for a single storey extension but the architect suggested a basement below the extension as the garden is on a downward hill.

I have sent some rough drawings to some local builders to get an estimate but wanted to get some ideas from the forum members on what to expect/look out for.

So the proposal is for a 4m x 11m single storey extension with a 6m x 11m basement extension. This will include underpinning the back wall of the current cost. The basement will include a utility and bathroom so will require plumbing and electrics etc.

Given the size - can someone give me a rough guideline price on what to expect to build such an extension?

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Your post is pretty vague, what is your spec of the underpinning and how much of is there to be done? That's 110m2 so pretty big, in my experience these kinds of jobs cost the earth and are generally not financially viable unless the house is a forever house or in a posh postcode. I'd expect £140k easy.
Sorry, I didn’t haven’t any more details as the architect needs to dig pilot holes to assess the current foundations, but he is confident that the current house foundations are already a metre and a half - 2m deep.

This is our forever house and we will eventually have our elderly Parents move in so the space would be very well utilised.

thank you doe the approx cost

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