Primary System (Siphonic system)
As a safety precaution, it is recommended to provide overflow systems to gutters or roofs where risk of overflow (due to blockage or extreme rainfall) cannot be tolerated.
Overflow systems can generally be of 2 types;
- Overflow weirs
- Secondary piped systems.
In the case of roofs with secondary piped overflow systems, the primary system refers to the main system that is designed to work most of the time while the secondary system acts as a backup for either blockage or for extreme rainfall that exceeds the design capacity of the primary system.
Primary and secondary siphonic systems should operate completely independently of each other. The primary system can be designed to deal with all lower return period of storms up to specified rainfall intensity. Secondary system will deal with more intense storms up to the maximum design intensity for the scheme. This can be achieved by preventing flow from entering the outlets of the secondary system until water levels in the gutter or flat roof exceed a certain limit.[1]
References
- ↑ BS 8490:2007 Guide to siphonic roof drainage system
