Newcastle Nobbys Signal Station has been recording rain since 1862: 1124.6 mm a year, spread across 98.1 days that reach a millimetre or more. Gutters, downpipes and flashings here are working equipment rather than trim. Licensing runs differently from the rest of the water trades, and the difference catches people out. The Home Building Act 1989's first limb of specialist work reads plumbing and drainage work other than roof plumbing work, so roof plumbing sits in residential building work as a trade category under the Home Building Regulation 2014 — and picks up the $5,000 threshold that ordinary plumbing never touches.
The category boundaries on a roof follow the material, and the Home Building Regulation 2014 draws them precisely. Roof plumbing covers the fixing, installation, renovation, alteration, repair and maintenance of guttering, downpipes, roof flashing and roof coverings — except coverings of non-metallic tiles and slates, glass, concrete, timber, thatching, or malthoid, bituminous or similar membrane. Those exceptions are why roof tiling and roof slating exist as separate trade categories, each with its own scope covering the fixing of tiles or slates and the associated flashing, sarking, batten and valley work. The register displays these as Roof Plumber, Roof Tiler and Roof Slater. In an apartment the line moves again: the statutory Common Property Memorandum places guttering and membranes on the owners corporation's side of the maintenance split, where the scheme's by-laws have adopted that memorandum, which puts most roof drainage work outside an individual owner's control.