Imperial College London's main student accommodation comprises six first-year undergraduate halls of residence around West London, primarily South Kensington and North Acton. Accommodation in these halls is generally for first-year undergraduates only, although some students may return as "hall seniors" with operational responsibilities and there are three halls available for continuing students. Halls are run by wardens who are members of staff, along with sub-wardens who are PhD students. Silwood Park halls are postgraduate, but only cater for students studying on the Silwood Park postgraduate site in Berkshire.