Shielding will help reduce hum with single coils, but it will rarely reduce it completely. Obviously make sure the foil is properly grounded and don't forget to ground the underside of your scratchplate. I always do the whole undersurface. I run copper tape up from the control cavity (there's normally no gap between the control plate and the scratchplate so you can't see it) and across the top of the guitar to the neck pickup cavity, with plenty of copper around the neck pickup to make contact with the scratchplate copper.

Then it's all down to how electrically noisy your playing environment is. Playing at home I rarely get any noise from my single-coil guitars unless I'm too near the amp.