This feels like a very dumb question , but we've been doing our house cost calculations on the basis of price per square metre, and all the way along, I've been measuring the dimensions of our floor plans from the outside.
I've just noticed that quite a number of project home floor plans measure internal floor space.
Is there an industry standard on whether $/m2 is on internal floor space or total building footprint?? Calculating on 200mm (minimum) thicknesses, external walls add up to many extra metres.
In our case, if I've been calculating things the wrong way, we could have extra tens of thousands to play with! I'd be delighted to find out I've stuffed up! But I suspect I won't be.
Yours hopefully
e.