cost of double storey extension

vlbrennan1980

7 years ago

hi, we are looking to design a small double storey extension of 2m x 5m, however we've been given 2 calculations for a rough guide for the extension (Inc plastered walls and basic electrics):
1 - width 2m x length 5m x £1,600 = £16,000 + 50% to do second level = £24,000. OR
2 - width 2m x length 5m x height 3m x £1,600 = £48,000 x 2 to do second level = £96,000
both plus vat plus 10% for wastage, BUT both seem extreme ends of cost spectrum (too cheap / too expensive), any idea how to get a rough idea and calculation to use????

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PRO

User

7 years ago

The general rule of thumb used to be 1000 per square metre, this has risen in recent years to around £1500 - finished, that includes all materials, plaster down to every socket and switch. There are a few online calculation tools available but i would imagine that you should be looking at around £40-60K depending on the roof type and finish expected. Just as a point of interest, your 2m width is very small. 2 metres would normally be the outside of the walls, and when you allow for block / brick and a void for the insulation to sit in the middle, then plaserboard, plaster etc, the interior size is going to be much less. If you want a floor area of 2 metres, make sure your builder understands that the external dimension still needs to be worked out. Or if you only have two metres of space to build on as your builder how much depth you're losing. I think the current standard minimum is 30cm ( 300mm ). Thus your internal would be 1.7m ( approx 1ft less space )

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Comments (6)

vlbrennan1980
Original Author
7 years ago
thank you so much, really appreciate your feedback and time, yeah it is a small width (just to do a small snug / home office on one half of the 5m and then in the other half a downstairs toilet / utility room), upstairs will be making a bedroom wider with a small ensuite :-)
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PRO
User
7 years ago
It all depends where are you based. In London £1,600 per square meter is a very decent price for a single storey, naturally + VAT. Second storey will be 50% more. In my opinion £24k is very reasonable and £96k is absolutely over the top!
PRO
Oasys Property Solutions
7 years ago
Magazines and television programmes love costing extensions on a square meter basis. However, I find this to be fairly inaccurate. For example, if you wanted to add a 1m2 pantry, this isn't going to cost £1600. Conversely, it's not going to cost 25% more to extend 5m instead of 4m on a rear extension. In short, whilst some elements are scalable (e.g. flooring), others are not (e.g. site facilities, including storage, toilet hire).

Your extension is a relatively small footprint and consequently any complications are going to have a far greater bearing on the cost. Examples include soil, party wall detailing (if applicable), floor construction, material choices etc., and of course location.

I would refer back to whoever drew up the plans, but with such a variance in price, perhaps it would be worth calling on the services of a quantity surveyor.
PRO
Style Within Limited
7 years ago
These comments are all helpful. A local builder will also have a shrewd understanding of how much things cost, and he or she will usually offer budgetary advice for free. We have gathered data over the past 11 years of our home renovations in the West Country and published actual prices from real projects on our website, which you may find of interest. All of the larger renovation prices were derived competitively. We have been sharing this information to help people understand the likely cost of renovation (before going too far) against a summary of what each project entailed - readers can then interpolate or extrapolate to budgetary figures for their particular project. - I hope this link works if you click on it, click here or just visit the Style Within website. Best wishes. Nick
katty smith
7 years ago
Great now I can see you too Dom.

cost of double storey extension

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vlbrennan1980
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cost of double storey extension

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vlbrennan1980Original Author

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vlbrennan1980
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