Extension cost

[David2749]

My daughter just bought a house that she wants to extend on the back of. It's basically knock down the small extension that's there now and built the full width of the back of the house , 5.5 x 3m single story with a rsj supporting the external back wall of the house with a flat roof.
I realise it's difficult giving me some idea of what it might cost, but the estimates she has been given to date are £22k and £55k.

What's your thoughts?

 

[RandomGrinch]

I'm not an expert, but I'm sure the cost could be anywhere in that range (and above!), depending on your choices (although 22k sounds a bit cheap!).
If you were to make the rear wall a fully opening bi-fold door system, then it's definitely nearer the top-end!
We might not have enough information to go on yet!

 

[David2749]

Thanks for your feedback, I agree it's difficult without seeing what's to be done, but after having 3 quotes there seems such a variance from top to bottom. Each builder is from a reputable company apparently!!

 

[RandomGrinch]

Thanks for your feedback, I agree it's difficult without seeing what's to be done, but after having 3 quotes there seems such a variance from top to bottom. Each builder is from a reputable company apparently!!

Has there been a proper set of plans drawn up?
If so, the variance is quite dramatic. The builders should be quoting from the plans.
If not, it is understanable, they may be picking numbers from the air and the true cost could be quite different!

 

[David2749]

There haven't been any plans drawn up yet, so that's my concern. I've not spoken to any if the builders as I don't live close to my daughters place, but such a variance is questionable.
I know bi folding doors are expensive but a friend has one fitted which was a 5 door and this cost £5k. So not cheap.

 

[RandomGrinch]

Ok,
Without plans, you are not comparing 'eggs with eggs'!
That variance is understandable.
Personally, I would get plans drawn up and a structural engineer to specify the RSJ. (This info will probably be needed for building control etc. anyway)
Without plans you are relying completely on the builders competance and experience.
That is not always the best idea!

...also, if you want a better range of responses, try posting in the 'building' forum.

 

[opps]

I know bi folding doors are expensive but a friend has one fitted which was a 5 door and this cost £5k. So not cheap.

The house where I am working they were £20K (three panel sliding, approx 3m tall).

I have to agree with the replies above which state that each builder might be quoting for something slightly different.

 

[cwhaley]

I am having an extension of exactly the same size (3m x 5.5m) which is nearing completion. I cleared the site and dug the foundations to 1m, which was two full weekends of work.

I asked the builders to complete as a shell, which includes walls, roof, French door, two windows, one skylight and a concrete floor. Total cost was £14.5k, not including the cost of building control and Severn Trent (combined cost of about £890).

Like you my quotes varied by up to £10k north of that figure! I don't have plans from an architect as it's such a small project, but having something to go from is essential so I knocked up a dated scaled drawing of each elevation on Google Sketchup. It meant we could refer to something as it was being built.

Should we want to open up what was the old back of the house in the future (unsure yet due to room layout) several builders quoted between £1k and £2k (span of only three metres).

The rest of the work will be completed by myself, apart from the electrics which will be done by a qualified spark. I've budgeted £10k which I'm hoping is more than enough!

 

[sxturbo]

My parents had an extension this size 2 years ago, cost them 35k, that was only upto a plastered finish and a new consumer unit, a new boiler and 2 rads installed and working in the extension. My dad installed the kitchen done the painting and all the architraves and skirting.

This was in Southend which is considered London waiting, so the prices are probably dearer than the north.

That price now would be roughly 45-50k

 

[Bonni]

My daughter just bought a house that she wants to extend on the back of. It's basically knock down the small extension that's there now and built the full width of the back of the house , 5.5 x 3m single story with a rsj supporting the external back wall of the house with a flat roof.
I realise it's difficult giving me some idea of what it might cost, but the estimates she has been given to date are £22k and £55k.

What's your thoughts?

Without seeing the plans, £33,000 to £39,000. But that's up North price and will exclude any bi-fold door cost as these vary. With the price of wood etc.. you might be surprised at the cost price of a warm flat roof.