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Guidance Document 21 Guidance on selecting the correct rainfall intensity

Publication Year

2026

Document Status

Current

Abstract

Advice on safe and effective roof drainage systems design, covering UK Standards, risk categories and building lifespan, and rainfall graphs.

Document History

June 2026 edition. Supersedes 2022 edition. First published as Information Data Sheet GD 21 on July 2018.

Publisher Information

Metal Gutter Manufacturers Association

Formed in 1994, the Metal Gutter Manufacturers Association represents UK manufacturers of metal gutters.