Designing Roof Drainage

Correct design of a roof drainage system is critical to the waterproofing of a building. This is a task that should only be carried out by a suitably qualified trade professional in accordance with the BCA and Australian Standards.

In the design and detailing of a roof drainage system, consideration must be given to a range of factors such as:

• rainfall intensity
• roof catchment area
• gutter size/capacity
• gutter fall
• gutter outlets (sumps, rain heads, nozzles)
• downpipe size, quantity and placement
• overflow consideration
• material selection and
• jointing

View information on the design of roof drainage systems:

• Download Office of Fair Trading Residential Gutters Quick Reference Installation Guide (174 KB)
• Download Using LYSAGHT® Roofing & Walling - Chapter 2 Design Preliminaries (1090 KB)
• Download Using LYSAGHT® Roofing & Walling - Chapter 6 Roof Drainage (541 KB)
• Download Gutter Overflow Leaflet (327 KB)

Downpipe Design

The downpipe size and spacing should be determined in accordance with AS/NZ3500.3.2:1998 National plumbing and drainage: Part 3.2: Stormwater drainage - Acceptable solutions.