Cost of Extension

[dogfonos]

Would appreciate opinions on the cost of a planned single storey extension.

I've seen a rule-of-thumb figure, based on external area of build, of £2,000 per sq meter for S.E. England in 2016 which excluded sanitary ware, kitchen units/sinks/appliances and decoration (not sure about windows/doors?).

I've received a couple of quotes so far for a 32 sqm extension (measured externally) and they're both in the region of £2,400 per sqm (excl. all windows and internal & external doors).

NB. Extension will be tiled pitched roof. Strip foundations need to be almost twice average depth in a couple of places. Beam and block flooring.

 

[noseall]

No idea, I live in the Midlands. We look at a typical figure of £1000 - £1200 p/m² up here. £1200 may be enough to include leccy and plumb and would definitely include windows.

 

[foxhole]

Lots of variables , have done most of my place and by those prices should have cost me £150,000 , have spent over £120,000 but doing most of it myself with help from builder son-in law who worked for a day rate. But just shifting the muck took 15 grab lorries at £260 a load plus a few skips.Flank wall we intended to hold up while we slipped in a large steel , but due the poor brickwork we ended up having to knock out the entire flank and rebuilding.Also my foundation hit a slurry of clay so we had to go deeper and also add steelwork to build a raft foundation which all came as unexpected costs.

 

[^woody^]

Who quotes and leaves out the windows?

None standard foundations can bump up costs disproportionately.

 

[dogfonos]

Thanks for your replies.

Interesting to note that rebuilding costs of the entire bungalow is given as £194,000 (for 103 sq meter footprint property and average quality fixtures & fittings in my S.E. England postcode) on the Royal Institution of Chartered Surveyors Building Cost Information Service domestic bld. calculator. The cost of the proposed finished build will clearly get into six figures. So increasing the space by just under a third will cost over half the price of rebuilding the entire property!

Who quotes and leaves out the windows?

There's a reason for that. I asked the builder for a quote that didn't include supply and fitting of windows and external doors because I've already sourced them. The window & door manufacturer/supplier only gives a guarantee if they fit them themselves and the quote the manufacturer/supplier has given me is for 'supply and fit'. Same situation with another door & window manufacturer/supplier that I was also considering.

 

[tomfe]

That calculator is very basic and does not take into consideration anything other than the building type.
It's more expensive to build small then large, so for example a 10m2 extension will not cost half that of a 20m2 extension.
I second around £1200-£1500 for a starting point however this, as already said, can change dramatically with access, how busy builders are, finish, construction type etc etc
Maybe pop your BC drawing up so we can give you a better indication of price.

 

[noseall]

Interesting to note that rebuilding costs of the entire bungalow is given as £194,000 .

Does that include demolitions, spoil removal etc?
Don't forget that the drains and foundations will already be in place on a re-build.

 

[stuart45]

The calculator does allow for new foundations and drainage. On the free one it makes assumptions, on the one you pay for you have to put in the length of drainage, number of manholes etc, plus perimeter wall details, paving etc.