I have a double brick and cavity type walls and I would like to build a second floor extension an top. The inner leaf of brickwork carries the concrete tiled roof at present. This wall is constructed from horizontally cored clay bricks. Is it possible to support the upper floor loads on this wall?
From the post, I'll make two assumptions. You're from, "down under" and you have no wood framing. I would consult a local engineer or architect for the weight bearing abilities of your construction.
Very few people who post on the internet know their rear end from their outback.
Any time you more than double the load, I would be very suspicious of the ability of a single leaf (or wythe) of brick supporting more than twice the vertical load.
Brick are really not cored horizontally, but are rotated 90 drgrees when laying for some reason (it could be for ventining a cavity), but the load capaicty is usually reduced. You probably have some Boral brick (manufactured by Boral or an acquired country), but the manufacturing process has not changed.
You need alocal structural engineer to give you some options.