Grandad annex - cost to add an upstairs

Furn462

I am currently at the very early stages of planning a new build grandad annex and looking at designs and costs. We have settled on having a single storey design with a pitched roof. We are keen to make the annex as flexible as possible going forward and are therefore investigating adding a first floor to half of the building (sort of a mezzanine style) with the other half being double height.

Does anybody know, in percentage terms, how much adding the first floor is likely to add on to the cost of building a straight bungalow? I would hope that given that the roof structure is there anyway the additional costs wouldn't exceed 50% of the bungalow cost alone.

Many thanks in advance.

iamcornholio

Upper floors will be roughly 2/3 the m2 cost of the ground floor. But it all depends on the design.

I don't fully understand your concept of "adding a first floor to half of the building ..... with the other half being double height". If you add any floor, wont all the building become double height? Introducing complex, or non-standard design could well add extra cost

But remember that older people and stairs don't mix too well, and best to avoid double storey granny annexes if possible