Technical Booklet C Site Preparation and Resistance to Contaminants and Moisture·Page 37·7.1
General requirements for roofs
Roofs must resist moisture from weather entering the building and prevent water damage to any building components.
Roofs should –
(a) resist the passage of moisture caused by the weather to the inside of the building; and
(b) not be damaged by the weather and not carry precipitation to any part of the building which would be damaged by it.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet C - Site Preparation and Resistance to Contaminants and Moisture.pdf