another extension question

[silverfrog]

we are looking at getting some work done on our (old, crumbling) house.

the main thing we want to do is extend, but not building an extension as such.

the house as it is is 3 storeys. the ground floor has had an extension built already (the kitchen - about 8ft by 14 foot). we want to push out the upper 2 floors of the house to make the back of the house square, iyswim. currently there is a steep roof pitch down to the kitchen ceiling, then a slightly shallower roof for the ground floor.

what sort of cost would we be looking at for adding these upper levels? I know typical extension costs = £1-1.5k/sq m for a single storey, but we alreadu have that. we want the current roof taking out, the walls of the 1st/2nd floor pushing back, and then re-roofing in appropriate manner - what sort of rough guide should we use for pricing that?

also, we would ideally have some internal remodelling done - what sort of costs for taking out walls and putting in rsjs? we had similar work done on a previous house, but it was done chaotically and piecemeal (there was a lot going on in our lives at the time) and I think we paid massively over the odds - would like to avoid that this time (we are unfortunately in an area which attracts an instant postcode price hike)

I think the biggest question (and therefore impact on cost) would be whether the current foundations for the ground floor extension are deep enough to support 3 storeys. I doubt they would be unless whoever had them done originally intended to go up at a later stage. Must stress I am not an expert by any means but I think you probably need to check that before anyone can give you even a rough estimate.

the foundations are probably ok (obviosuly we need to verify this)

it is likely that the kitchen is original, rathe rthan an extension (I described it that way as easier to picture what I meant). most houses in the road (all built within 20 years of each other originally) have done similar, ours is one of the last to not have been extended/built up. none have had problems with foundations.