The Lemon Fool

Hi

I'm considering buying a house which has planning permission for a 2 storey rear extension meausuring 5m x 9m. Assuming for the purposes of this conversation a build cost of £1500 per square metre, does that give me a build cost of £67.5k or £135k, i.e. is it based on footprint or total new square footage? I can speak to a builder on Monday but just thought I'd ask on here, couldn't find a definitive answer elsewhere.

Obviously this is just the build cost and there are many other costs to consider but I can probably handle that on the first price, not the second. I've a funny feeling though the answer is the second.

thanks
heathmount

Two stories if you're in the industry

£60/FT2 + 15% vat x 10.77 x 2 = £1,486/m2

AiY(D)

Hi AIY

Thanks for responding. I assume you're showing me that £60 a square foot is the same as £1500 a square metre. Not sure what "Two stories if you're in the industry" means. Think I still need an explanation

Sorry.

For clarity that's the build cost for two stories - very broad brush of course - and that's for builders. Margin and overheads will increase that number.

9 x 5 = 45m2 - one floor x £750/m2 = 34K
45 x 2 = 90m2 - two floors x £750/m2 = £68K

£60/FT2 + vat = £69/FT2

When measuring FT2 (Quantity Surveyors & House Builders) measure internal floor area on both floors and multiply by the price per FT2 or M2. So the price you have been given "should" be to build two floors or 90m2. Failing which you live in the middle of London (somewhere like Chelsea) and the price is double what it should be.

Depending where you are, the specification, the design and the difficulty getting plant and materials around the site this "ball park figure" will move quite dramatically.

There's a huge amount of price inflation in the industry currently and I suspect the FT/2 price has edged up accordingly.

I live in Yorkshire and I'd budget that sort of build at £100K. There are so many variables though.

AiY(D)

AsleepInYorkshire wrote:I live in Yorkshire and I'd budget that sort of build at £100K. There are so many variables though.

We did a conversion of the barn at the back of our house in Devon. It was about 1,000 square feet with 3 bedrooms and 2 bathrooms. The quote was in the region of £120,000 so that sounds like the same ballpark.

Access was a little tricky, via a narrow lane down the side of the house, small vehicles only, so that probably added a bit.

heathmount wrote:Hi

I'm considering buying a house which has planning permission for a 2 storey rear extension meausuring 5m x 9m. Assuming for the purposes of this conversation a build cost of £1500 per square metre, does that give me a build cost of £67.5k or £135k, i.e. is it based on footprint or total new square footage? I can speak to a builder on Monday but just thought I'd ask on here, couldn't find a definitive answer elsewhere.

Obviously this is just the build cost and there are many other costs to consider but I can probably handle that on the first price, not the second. I've a funny feeling though the answer is the second.

thanks
heathmount

£135k based on your assumption. But where does that assumption come from?

(The use of both metres and feet just confuses.)

It's not just a question of the extension as works will probably be required to the original building to accommodate stairs and presumably to knock down a cavity wall between the existing and new structures plus various drainage and plumbing alterations. Thus an estimate based on the square footage of the new structure could be wildly inaccurate.

Hi, thanks for the responses.
We’re not going ahead with purchase for various reasons which aren’t relevant for this conversation. However I think anyone reading this thread whose hasn’t done an extension would still be confused.

So: I’m not saying £1500 a square metre is an accurate estimate. I’m not even asking what £1500 a square meter will get you outside of a brick structure and (possibly) a roof. I don’t care about windows/bathrooms/ electrics/plumbing/ skips/insurance/ etc.

I’m just asking when The Internet fairly consistently says that the average 2 storey extension costs £1500 a square metre (subject to quality of finish and location) then if I have an extension that has a footprint of 5m x 9m then is that 45 square metres or 90 square metres.

AiY suggest it is 45
Dealtn suggests it is 90

Clearly in practise I would speak to a builder for a quote but as the £1500 figure is bandied about on the internet so often I would imagined there would be a standard answer.

Thanks
Heathmount

heathmount wrote:Hi, thanks for the responses.
We’re not going ahead with purchase for various reasons which aren’t relevant for this conversation. However I think anyone reading this thread whose hasn’t done an extension would still be confused.

So: I’m not saying £1500 a square metre is an accurate estimate. I’m not even asking what £1500 a square meter will get you outside of a brick structure and (possibly) a roof. I don’t care about windows/bathrooms/ electrics/plumbing/ skips/insurance/ etc.

I’m just asking when The Internet fairly consistently says that the average 2 storey extension costs £1500 a square metre (subject to quality of finish and location) then if I have an extension that has a footprint of 5m x 9m then is that 45 square metres or 90 square metres.

AiY suggest it is 45
Dealtn suggests it is 90

Clearly in practise I would speak to a builder for a quote but as the £1500 figure is bandied about on the internet so often I would imagined there would be a standard answer.

Thanks
Heathmount

I've worked in construction for 42 years. I started life as a Trainee Quantity Surveyor.

I'm sorry there is no standard answer.

AiY(D)