When I bought this 40-yr old 2-storey house (here in Canada) a couple of
years ago, was told the floor area is 1800 sq ft. Lately I measured from
inside wall-to-wall for getting estimate for attic insulation, it's smaller
than that (less than 1750). I think this is the "interior floor area" used
for "house for sale". Is there a standard way for the measurement?

Thanks,

John