Nbn En 12056-3 Jun 2026

Providing a step-by-step method to assess if non-siphonic roof drainage components (gutters and downpipes) are large enough to handle expected rainfall.

A steep pitched roof has a larger sloped area, but rain falls vertically. Using the sloped area oversizes the system, leading to unnecessary cost. The standard says: use the only. nbn en 12056-3

Importantly, it cover siphonic roof drainage (which falls under a separate technical agreement, often EN 12566 or specific national approvals) or drainage of paved areas at ground level. Providing a step-by-step method to assess if non-siphonic