advice needed on price for a single storey back extension

4 years ago

We bought a house with a very long extension which is only half the width of the house. There is also a very small galley kitchen. The plan is to increase the floor space by knocking the side wall of the extension and take it right across the width of the house and to convert the existing kitchen into a shower room and utility room. The measurement of the new space at the back would be 31.70sqm and the new shower room/utility room would be 12.41sqm. How mu much would you expect to pay for such a renovation?? We live in Oxford and builders seem to be quite keen to charge a very high price. Has anyone got any advice??

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Maths Wife

4 years ago

Usual workings dependent on area are around £1500-2000 per sqm finished with walls plastered. That will not include your bathroom or utility fixtures, but would normally include standard light fittings ( white plastic ones ) and plug sockets. So I guess at the lower figure it would be around £65K and the upper figure £90k

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summerfieldapril7
Original Author
4 years ago
This is what the plan looks like. Disregards the U shaped kitchen as we will be having an L shaped one with an island.
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Are you aware that building a 'L' shape extension will need planning permission first, this will set you back another 3-4 months. Plus Building Regs would need reapplying for. Also, from my experience conservatories only need building regs approval if they are over 30sqm; which means most conservatories are shoddy built and the foundations are unlikely to be suitable for the transformation into a proper extension. Also, the floor is unlikely to have been insulated - sorry but conservatories can be a hornets nest of problems. My advice is yes you should have a door off the hallway into the new room, cost of that should be minimal as you are only looking at using a couple of standard concrete lintels which are cheap as chips! Although I would have put the shower room at the front as the current layout means friends and visitors end up going through your kitchen to use the convenience. It has the advantage the new reception room as a rear garden outlook. Hope that helps
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Maths Wife
4 years ago
last modified: 4 years ago
There's an estimating tool on this website, Home Builiding.co.uk you could try that.

It also explains what costs a lot, what doesn't , what to look out for and give you an idea of the overall cost.

Also, if you go on a website called www.mybuilder.co.uk you can post your project and get quotes from local builders as you already have plan.

I'm guessing that you weren't expecting it to cost what they're saying as you've had quotes already.

How much were the quotes out of interest? and, did they fall within the range that I gave you yesterday?
summerfieldapril7
Original Author
4 years ago
<?xml version="1.0" encoding="UTF-8"?><md>Hi Maths wife,
Thanks for the website where I can calculate the cost......I have just done it!!
Maths Wife
4 years ago
Can't read some of your post summerfield, but well done! What did it say?
summerfieldapril7
Original Author
4 years ago
the rest of the post said....quote given was £97000 for demolition/knockthrough and.......evaluation price for total project was £174411!!!
Maths Wife
4 years ago
The 97K I can well believe, it's a big extension, but £174K, what on earth did you add to get to that, wow!! That's a hell of a lot!
summerfieldapril7
Original Author
4 years ago
I did not add anything....the website did!!
PRO
i-architect
4 years ago
Hi Summerfield!

Different places have different price points depending on the availability of labour and the cost of living. I imagine Oxford would be relatively expensive.

Typically I use a £2k-£2.5k per square meter basic cost price as a guide for initial design ideas for new-build and expensive areas like kitchens and bathrooms. Then a lower figure per square meter for simple refurbishing and reconfiguration of existing areas - around £1.1k-1.8k depending a lot of quality of finish required, specialist work needed, etc. This is for Cheshire and Manchester, where I do most of my work and we have quite a lot of builders but limited numbers of really good builders.

After initial sketch design I would get some indicative costs, possibly as a quote from a builder or from an estimator, then reassess the design and make adjustments as necessary to meet the budget. This is typically called "value engineering" in the construction industry.

For you to get the best prices that you can then you will need to have detailed plans, at least building control level of detail. Because with less detail than this the builders will be making their own assumptions and you may or may not want things to be as they assume. Spending more time and money up front getting the design right and putting the information together for builders to price up will usually save you money in the long run.

Hope this helps. Jane :)
PRO
Projection Architects
4 years ago
Hello Summerfield,

Hope you are well and the process of choosing a builder and limiting the works to your budget is not being a pain for you.

In my experience, as Maths-wife and i-architect have said, the total cost of the construction depends on the quality you look for and the market situation or even availability of builders. Sometimes it is more expensive to build because they are busier and they ask more for the same work, or just because they don't have experience doing what you are asking them to do. Also, usually good builders are more expensive, because they know they will have work even if they ask for more money.

Independently of those circumstances, a good way to calculate the overall cost of the construction for a standard work would be the following:

For an extension we estimate around £1800-£2000/sqm. If you are extending/refurbishing around 40sqm, then it would be around £80k just for the foundation, structure, walls, (have in mind that you have a very long metal beam in the design, and it is more expensive to install too).

On top of that you have to add the cost of the kitchen (it could be around £15000 including appliances and the kitchen island), the utility and bathroom (£5k each), and the bifolding door (usually I estimate £1000 per panel as average, including supply and installation).

Finally, I add around £800-£1000 per skylight (supply and installation too).

Adding all of it you could have an idea of the maximum they should ask you for it. Obviously this is including their profit, labour, materials, etc and you can find something cheaper depending, as described above, on the market and each particular construction company.

Hope it helped.

Wish you all the best!
summerfieldapril7
Original Author
4 years ago
Thank you so much for all the advice. It is really useful.

advice needed on price for a single storey back extension

Maths Wife

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advice needed on price for a single storey back extension

Maths Wife

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