Cost of Building Bedroom Extension

I was thinking of maybe having a bedroom extension built.
It would be on the 1st floor and on top of an already existing flat roof kitchen extension. I don't know if the foundations of the kitchen extension were designed to hold the weight of an additional floor as it was already built.
The extension would be approximately 7ft x 7ft built of blocks and pebble dashed. The wall of the house which would have to be knocked out to extend outwards would be (I assume) a load bearing wall as it is an external wall).
Was just wondering if anyone would know roughly what it might cost to build such a bedroom extension. Just a vague idea...
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SuzySue wrote:

Its impossible to say without knowing if the existing flat roofed kitchen extension would take the weight of the new 1st floor. Could be 10-20k for a simple job depending on where you live. A friend of mine had 2 rooms put on top of existing integral garage, which could take the weight. His is about double your floor area and it cost 30k, in the midlands.
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BillR wrote:

Budget at about 80 quid a square foot, and you won't be far off.

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7ft x 7ft I SqFt 49 x 80 = 3920
So, maybe 4000. That's not bad, I was thinking it might cost a lot more. If I could get it done for something like this, I might get a few builders in to give some quotes. BTW, I'm up north where I assume building work is possibly cheaper (?)
BTW, how do I know if the foundations of the existing kitchen extension are capable of holding an extension on top? Would the builders know, or would I have to get an architect or surveyor to do a survey?
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SuzySue wrote:

Even if they are not, the price quoted is for full demolish and redigging of foundations.
Unless its just a small area, its nearly always cheaper to prop, knock down and scrape rather than underpin.
What costs is not teh zie of teh work per se- materials are only at best 30% of teh cost. What costs is fiidly stuff - and detail finishing.
I could not envisage doing a kitchen fitout for much less than 2 grand, never mind the structure...
I think I was about halfway through the costs when I had a roofed structure with boarded out walls and wndows etc. The rest was in the fitout.
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SuzySue wrote:

A general point. Double the costs and timescales that a builder gives you. Experience shows this is about right mostly. Unless you go to a big firm and draw up an expensive contract, which will be for slightly more than double the amount that a jobbing builder quoted you, and estimated twice as long...:-)
The only other way is to do it a few times and take contol yourself. Then you can get it nearer estimates.
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Only the building control officer will tell you if your foundations are adequate - you will need a trial hole and perhaps a formal Building Regulation application to get him to comment officially.
Those rates appear way too low for even an approximate estimate. They do not account for working a first floor level, scaffold, new ceiling/floor joists, demolition and supports etc.
dg

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If the foundation needs underpinning then this can add 000's to the cost. Or even make it not viable (shifting clay or a raft required?)
If access is limited or there are other specific site conditions which mean the builder is going to spend an extra week there, then this too will bump up the price.
A pitched roof can be 33% more than a flat one.
So your 15,000 estimate quickly turns into a 30,000 quote. Or it puts you off doing it, when in fact you could get it done for 10,000
You really need a local builder to look at it and give an estimate based on his past experience.
You won't get an accurate/meaningful estimate here I'm afraid
dg

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