Awning fixed to existing brick retaining wall

Question

I am constructing a flat roofed (scillion) awning. The highest point of the awning is attacked to the house and the lowest point is supported by 90 x 90 timber posts. These posts are on metal feet which are sitting on top of a existing brick retaining wall which is about 700mm high and 300mm thick.
My question is, how long of a bolt will I have to use to attach these metal feet to the wall or how deep will I have to drill and use a threaded rod to aquire sufficient strenght to stop the up draft effect from lifting up the awning.
Hope you can help
Regards Shane