These developed as a matter of course; the earlier asylums routed all pipework through the ceiling space creating a cluttered and untidy look. With the advent of gas, and then electricity, the need for dedicated service tunnels became more pressing, and the larger asylums at the turn of the century had impressive networks of wide and airy tunnels.

Some underground spaces were found under the corridor asylum, although nothing contiguous, and it looked like most services were located at head-height in the main corridors.

Severalls was the complete opposite with an impressive system of tunnels, which thread under the main corridors and stretch over the entire site.