it is not the survey issue (kadastrovyj plan) but zoning and by-law. survey is the "picture" of your land and the dwelling (if any )on it.there is certain coverage of the land (usually up to 30 %0, as well as side backs).it is not up to rieltor to know all the by-laws.building on the exsisting foundaion is WAY cheaper than to build from the ground up. also, you do not to have to pay sewers, hydro water fees, etc. you can youse the same plate as your foundation in those areas affected by certain by-laws (lot coverage, set-backs, shadowing, trees, etc)