The existing window is either and oreil window supported by cantilever from the cavity wall in which case do not remove any brick/blockwork till you have temp supports for the bay.. or supported from the gallows brackets (more likely) but i would still prop the bay before you remove masonry..
Also you need to tie the new footings into the old by way of dowel bars and match the existing footing depth or the whole thing will move independant and crack internally..
Also you need to tie the new footings into the old by way of dowel bars and match the existing footing depth or the whole thing will move independant and crack internally..
