Technical Booklet C Site Preparation and Resistance to Contaminants and Moisture·Page 23·5.12
Suspended timber ground floors – general requirements
Suspended timber ground floors must resist moisture passage from the ground through ground coverage, ventilated air space, and damp proof courses between timber and moisture-carrying materials.
Any suspended timber floor next to the ground should meet the requirement to resist the passage of moisture from the ground if – (a) the ground is covered so as to resist moisture and prevent plant growth; (b) there is an adequately ventilated air space between the ground cover and the timber; and (c) there are damp proof courses between the timber and any material which can carry moisture from the ground.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet C - Site Preparation and Resistance to Contaminants and Moisture.pdf