Calculating house extension cost (rough)

3 Jun 2016
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United Kingdom

I'm buying my first house and already have some idea's about extending it. Basically it already has a ground floor half width kitchen extension and I'd like to extend all the way to the right of it across the back. I'd also like to add a two floor extension which would take the kitchen out another 8-10ft to the left and add a bedroom above, this would also require roof modifications.

Before I even start getting plans and builders giving quotes it would be really useful if I had some idea of the potential costs. Is there anyway of getting some approx costs. I'm not even sure if I'd be looking at 25K or 75K+ at the moment having never been involved with building work before.

Also any info on web sites with example extension plans or that help with producing rough plans so I could jot down some idea's would be most welcome. Something where I could draw the layout of the house, place sinks, toilets and so on really.

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Approx £1000-1200 per m2. Any break-throughs from the existing house, kitchens or bathrooms and all fees on top.
I haven't seen a website with actual plans on for extensions but there is a Youtube film with some different configurations which I found helpful. Taking a walk round your road is also useful.

The Housebuilders Bible is very good and even though it is primarily about new build extensions are covered in full. It is very good on how to cost a project.
Ah Ok thanks for the info, I will also take a look at the bible. I assume by m2 that is based on the floor area but I'm not sure how a 2nd story and roof work comes in to that ?
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swebb just be aware that with an older house there will be all sorts of complications and it is often a good idea to not rush into anything.

Common ones are moving the gas and electric meters, a new concrete floor in kitchen plus a new ceiling. Then you might need a new fusebox plus there are a few bits of damp to sort and before you know it you are looking at a lot of extras.

Something they don't tell you is builders always quote ex VAT.

I am not saying don't do it but as the kitchen is a very expensive area it will come out at the high end of your estimate unless you can do some of the work yourself.
Thanks for the info fella's. I plan to have a good think about any work on the house when I move in and decide what the priorities are and what I am willing to spend. The point about the gas and fuse boxes is useful as I hadn't even considered that!

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