Calculating size of extension

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Parazard2

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Hi got planning permission for a small single storey extension due to be built soon. The extension is 18.75m2 internal surface (4.075x4.600m) , 22m2 if the depth of the walls are taken into account in measuring it (4.600x4.600m). The planning permission states the extension is 18.75m2 but the builder is quoting for an extension that is 22m2. At 2k a m2 this is an expensive difference so I am wondering is there a consensus as to how the size of an extension is calculated?
 
I suspect that if you asked for a price based on the internal dimensions it would be exactly the same price - the price per m2 would be higher

I am sure the builder's cost is based on the amount of material and labour required and not a cost per m2
 
Planning deals with internal dimensions alright, builders usually include the overall size.

Get quotes from a few builders for comparison purposes. I'd be cautious with any builder just quoting 2k per sqm without a detailed works description, you might end with lots of extras that you assumed were included in the 2k!
 
The quote you got is for the internal floor area.
This is typical and the norm in the industry.

There's no such thing as a set price per square meter, its a rough figure to guide you in order to plan what size of an extension you can afford.

An 18.75 Sq. M extension is most likely coming in around the 45-50k mark i would imagine.
 
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