Smaller pipe diameters with a siphonic system can be used, reducing material costs.
Full-bore flow within the piping reduces pipe diameter as compared to open-channel, traditional gravity flow. The smaller pipe size equates to savings in material. For example, a traditionally designed system calls for an eight (8”) inch pipe, a siphonic system of equal drainage capacity may need only a four (4”) inch or six (6”) inch pipe to drain the same quantity of water.
Siphonic action permits level pipe installations allowing fewer vertical stacks, saving ground work and building costs.
Traditional systems are designed to be atmospheric throughout and rely on pipe gradient or pitch to induce flow to the point of discharge. This pitch necessitates the pipe elevation to become increasingly lower as it runs laterally. Full-bore flow is achieved independently of pipe gradient in a siphonic system. The piping can be installed flat like any other mechanical system such as sprinklers and it simplifies coordination with other building elements. With siphonic piping being horizontal, the building height may be reduced by 3 to 4 feet, saving on construction costs.
Driving head of the siphonic system is up to 100 times that of a traditional system (i.e. height of building vs. depth on roof).
Siphonic roof drainage systems make full use of a building’s roof height to drive the drainage capacity. The resulting higher operating velocities (3 ft/sec up to 30 ft/sec) of a siphonic system further reduce pipe size and promotes self-cleaning of debris.
In a siphonic system, below-slab installation costs are minimized, thus reducing excavation, backfill costs and exterior underground piping.
Level installation allows for longer lateral runs overhead thereby reducing or eliminating pipe installed below slab and the associated costs of excavation, bedding and backfill. If overhead, traditional drainage pipe has to quickly drop vertically to avoid a conflict with the ceiling, structural elements or HVAC systems. If below grade, the longer the horizontal run, the deeper the pipe trench must go to accommodate pitch. Siphonic systems reduce or eliminate these issues. This means there are lower site preparation costs.
Within a siphonic roof drain system, stack and horizontal pipe locations are highly flexible.
Level installation and freedom of placement of vertical stacks reduces buried pipe depths and the associated costs of trenching, bedding, shoring, and dewatering. The flexibility of stack placement also facilitates on-site rainwater harvesting by allowing flexibility for cistern locations either below or above ground.
A siphonic system allows for maximum use of open space without intrusion of drainage piping.
Smaller diameter piping conforming to structural and architectural lines present a less intrusive presence in an open area. Level installation and freedom of placement of vertical stacks reduces the size of exterior storm sewer infrastructure. The point of discharge for the roof can be concentrated to one corner typically rather than out the building at several points.
These benefits enable significant savings in terms of time and money. Large roof construction similar to those found on factories, warehouses, airports, convention centers, stadiums and “big box” retailers will realize the benefits of siphonic roof drainage and favor this type of roof drainage system. However, all buildings regardless of size or height can realize the economic and technical benefits offered by siphonic roof drainage.
