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Minimum Freeboard Values

In gutters where overflow can enter the structure, it is necessary to have freeboard to allow for wave action, obstructions, and other unforeseen circumstances. Capacity Calculations allow for these minimum freeboard values.

Minimum Freeboard Values

Gutter TypeFreeboard
Internal gutters30 mm
Secret gutters15 mm
Valleys > 8°15 mm
Valleys < 8°20 mm
Asymmetrical valleys20 mm
External Gutters with OverflowNo freeboard required
External gutters with no overflow15 mm
 
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Revision Category: 
3 - Substantial change to recommendation
Revision Detail: 

Updated table Minimum Freeboard Values.