On the extension wall, bed a timber plate on sand and cement at the correct height all round to accept the new joists. This is held down with galvanised restraining straps minimum 1 m long at 1200mm centres and screwed and plugged into the masonry . On the house wall you could use masonry hangers let into the wall but it can be tricky to get a nice level floor or flat roof. I prefer to bolt a timber the same depth as the new joists to the wall. Bolt with 12 mm studs at 500mm centres and chemical anchor resin. Ensure it is at the correct height. Use jiffy hangers to connect the new joists to the plate.
I hope this is of some help, obviously I can’t see the job and I’m making some assumptions.
Always check with the building inspector or engineer if you are unsure, they are there to help and often have preferred methods.