The house is not heritage, but is double brick with solid foundations.
I started with the architect as he is a friend of a friend so easy first contact. Very helpful guy, lots of info but didn't mention a knock down. So will now have chat with a of couple builders and see what they suggest.
Even thought the land is the expensive part, the only reason we would demolish and start again is if it was going to be more cost effective. Existing house has good street appeal and, as above, is of solid construction.
Is there a rule of thumb cost for demo, per square m2?
