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Single storey extension costing.

(16 Posts)
catpark Mon 20-Jun-11 17:07:08

We would really like an extension on our house as due to the property market we can't really afford to move. We currently live in a lower villa and all we want is our bathroom to become a shower room and hallway leading to the extension which would be a bedroom and new bathroom. In total it's only 16m2 (Footprint inside is just over 14m2) in total. We would want all electics, bathroom fittings etc. done as well.

We have contacted a few builders to get an idea on the costing before we get an architect to make drawings etc. incase it isn't affordable. But they won't give us an idea without the drawings ! Only one did and told us it would be £35 to £45 thousand ! Which considering the small size of the extension seems alot.

Anyone have a proper idea what sort of cost we could be looking at ? Also one of the mums at the school has told me that architects charge at least 20% of the build cost for drawings which seems excessive to me, any thoughts on this ?

Thanks in advance.x

said Mon 20-Jun-11 19:56:11

If you're clear on what you want, and don't think you need input from an architect, you can get drawings done by a structural engineer or an architect's technician (think that's what they're called) Basically, if you just need drawings you don't need an architect

Fizzylemonade Mon 20-Jun-11 21:34:30

I did my own drawing which the architect basically copied. I had already spoken to a builder as we knew him already.

Anyhooo he said basic costing for a single storey extension is £1k per 1msq. Then add £1k for the roof. So for my kitchen extension which is 2.5m wide by 3m long it would be £8.5k. That is for foundations, basic electrics and plumbing. I then have to factor in the cost of the kitchen units, flooring etc on top of that.

You can easily draw the extension yourself, I like to work with 1cm on the paper is 20cm on the ground so 5cm is 1m.

Your extension may involve moving drains and plumbing to drains, so that would cost more but only a few more thousand I would have thought. I think the £35-£45k mark may have been them covering themselves depending what you want.

Do your own drawing and go from there. My architect merely copied my drawing and submitted that to the planning office (kitchen extension and double garage conversion) charged me £400, then the builder project managed the garage conversion (kitchen not yet done, still saving up)

thisisyesterday Mon 20-Jun-11 21:36:45

we were told the same as fizzylemonade when we looked into it.

roughly £1k per sq.m

i think he also said that it doesn't cost that much more to do a double storey, because the main work is the foundations and roof and stuff...

jeanjeannie Tue 21-Jun-11 08:42:17

Yep - it's usually between £1k to £1.50K per Sq.m and thisisyesterday is right...the double storey doesn't cost that much more because of the reasons stated. Also building materials and things like skip hire have gone through the roof in the last 3 personally, I think you're better off going for £1.25k as an estimate.

You shouldn't need an architect....we use Google Sketch up as a rough starting point for people and it really makes it quick to see what you want in 3d.

Pendeen Tue 21-Jun-11 09:15:08

A very broad maxim is that, generally speaking, the smaller the project the greater the cost per sq m. I have worked on various extensions that varied in finished cost from £800 up to over £2,500 per sq m. There are so many other factors to consider as well.

BTW just be aware that Google sketchup or any of the free DIY drawing software, although useful and fun to play with will only produce what is no more than a picture - it is not a design. When it comes to the construction detail or obtaining Building Regulation approval, leaving such matters up to your builder can be risky unless you know them very well indeed.

Having said that (and not wishing to put me out of work) I have to agree with jj - for such a small job you may not need an Architect (but talking to someone with at least 7 years of education and intensive training behind them might be useful)!

vintageteacups Tue 21-Jun-11 09:25:15

We've worked out roughly that it'll cost between £40000 - £80000 to do our 2 storey extension, which will make a large kitchen diner with utility downstairs and vaulted ceiling master suite upstairs and new bathroom/landing/spare room layout upstairs.

I think your quote seems a lot but it hard to say.

jrg67 Tue 21-Jun-11 09:43:50

I am RIBA Chartered Architect, I would advise that you get a minimum of three separate prices from three builders. All should be given the same information, and asked to return there quotes at the same time. In addition I would advise that you use a "Minor Works" or "Intermediate" form of contract between you and the builder. You may choose not to use an architect, but I would suggest to you that you ensure that should you use a technician/plan drawer, that you ensure that they have the appropriate insurance in place to cover their work. On another point - if the works are finance by your bank/building society they may require the works to be inspected and signed off by an architect at various stages.

catpark Tue 21-Jun-11 09:52:40

Thanks all, can't get a 2 storey extension as it's a lower villa we live in so can't go up any further than half the height of the building. It is basically a box we want added to the back of our house and a small part of the drain needs moved.

I know the quote we got was exessive as further up the road are relatively new built house with fancy bricks and 2 storey extensions there are getting put up for under £50,000 and are about 4/5 times the size that we want !

I do have a sketch of what we want and a neighbour had plans made up for a similar extension but didn't get it done so we have those.

Is it the m2 inside or the m2 outside that they use to calculate cost as that could make a big difference in price.


jrg67 Tue 21-Jun-11 10:00:40

I would advise you to go by the external dimension. Could you get way with a storey and a half - i.e. the upper level built into the roof. Is there scope to drop the floor level on the extended portion to give you just that extra bit of height.

catpark Tue 21-Jun-11 10:13:12

No couldn't do that, not enough space.
It's a lower villa we have. We live in Scotland, don't know what they are called elsewere.
Basically in our building is 4 houses. 2 at the bottom with own front/back doors and gardens. And 2 live above, with their front door in each side of the building with their garden down the side of the building. So I can only build up to the halfway point of the wall. Upstairs neighbour can't build on top of any extension I have either as I own all the garden leading out from the back of my house. He can extend to the side but has to retain an access route for me for wheelie bin etc.

jeanjeannie Tue 21-Jun-11 10:14:35

Oh yes...don't use something like Sketch up as a subsitute...but it just can help to focus your mind and therefore plan properly - so that you get better quotes because you are more accurate with what you want. Changing your mind throughout the build (as we find often happens when there is no architect involved) often costs quite a bit of money!

Pendeen Tue 21-Jun-11 10:17:35

I would agree with jrg67, if you do get to the stage of appointing a builder ensure you use a recognised 'Standard Form of Contract'.

This would go a long way to protect yourself from many of the common problems / misunderstandings that often arise between builder and customer.

There is a contract specifically for domestic projects; the JCT Homeowner form HO/B (or HO/C if you do end up using an Architect) obtainable from and click on 'Homeowner'

Pendeen Tue 21-Jun-11 10:18:53

Scotland? Didn't realise you lived there.

Oops - different forms of contract, building regulations and so on apply in Scotland sorry.

jrg67 Tue 21-Jun-11 10:19:09

Apologies. Seems like you will have to go single storey. On your original thread regarding fees - 20% does seem excessive. These days you should be able to get everything - and by that I mean any required structural input etc... for half that figure. That would also include the preparation and applications to planning and for building warrants etc...

Thewhale2903 Fri 18-May-18 13:41:26

Hi, I know you put this post on quite a few years ago now but I was wondering how this turned out for you. We are in exactly the same position a 4 in a block and live in Scotland. We want to add a room onto our kitchen to be our living room to make our current living room as a third bedroom. How hard was it to get planning permission and how much did you have to spend if you went ahead?

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