I am definately NOT and expert on this area, but I know that when joining an existing house wiring when alum to copper fixtures, special care is required on the wire nut, the additive that you squeeze in to the wire nut and the fact that alum to copper joints need to be very very tight. Alum has a bad tendence to loosen as it heats and cools off and then you have problems.
Get the correct information when you home is alum wiring.