Single storey rear extension

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In the middle of purchasing a property and looking to extend it to the rear between 3.5 metres to 4 metres deep, 5.5 metres wide with a height of 2.5 metres with a flat roof (ply, roof membrane – felt ). The roof will be finished with parapet with with joists deep enough to accommodate a future first floor extension.

Therefore when I come to build the first floor extension if the need arises all I need to do is take the capping off the parapets, rip the felt off and extend up to my wall plate height.

The building works will be undertaken by my Dad who is a retired builder with my help on site. As hes not undertaken any building works for a number of years hes totally out of keeping with build costs. I talked to a friend who works for a building company and he stated the average going rate for an extension with labour is roughly £1000-1250/m2 which would be around 22-28k for my proposed extension.

Considering that there will be no labour cost would anyone have an idea of what the build cost would be?

Regarding Architect drawings a friend is drawing up plans.
I will be dealing with the planning application and building control application.
Party wall act I am aware of and can deal with that.

The house is a timber frame brick skinned dating from the 1970s and this may require some steel work when extending according to the building control off I spoke with today.
 
Seems rather dear for a foundation, 4 walls a bit of steel, and a flat roof.
What ground is the house on, do you need to pile?
Is your friend a chartered engineer, regarding the actual need for steelwork, as drawings won't be remotely helpful without knowing what's going in them?
 
The friend works for a national building company and manages all the building regs on large new estates. I would need to employ a engineer once I have spoken to Building Control on whats required
 
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a friend of mine who builds extensions reckons its roughly 1/3 materials 2/3 labour, going by that on a normal property you'd be looking at £8-£9k
as yours is timber framed prices could be a bit different.
he's nearly finished a 3mx3m on his own house and he's looking at ~£6k for the finished job, but that included some other mates working 'for a drink', i even got roped in myself to push some wheelbarrows of readymix round the back for the footings
 
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Can't help you with the build costs, we had a similar sized single storey flat roof extension 2 years ago and the total cost was 22k getting a lot of the building materials at cost, and paying normal labour costs.

This included extending the heating into the room, new rad, 2 meter upvc patio doors and sidelights, single door, 3 roof lights, flooring, electrics, lighting, boarding and skim.

Not sure if that helps at all...
 
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The price per metre square seems rather high if my memory serves correct. I know that £1k/m2 is the value a lot of developers tend to aim for when they do social/budget housing. Yours shouldn't be far off that.

You will definitely need structural engineering drawings and calcs to submit to Building Control. You will also need a drainage engineer's drawings/proposal for that aspect. Could well be the same person/company doing those two.

Do make it clear you want the whole thing designed to allow future extension!
 
1000 sqm is what I'd use for shell only
1500 sqm for a basic spec
2000 sqm for a good spec

Take 50/50 labour and materials and you shouldn't be far wrong with some change.

There is 10s of factors that could change it though so with your little detail will be rough guesses.

If you want a proper labour plant material split pm me
 
I had a shell done only and that cost £1000 per square meter. (brick build, windows, pitched roof and vaulted ceiling).

That did not include plumbing and electrics and gas, the later two been done by registered professionals.

Plaster on top of that and flooring.

It was better for me as I could spread the cost, however I do wish it could have been all done by one person for ease.
 
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