• Sections over 50,000 sq/ft must be
drained by two independent down
pipes
• Roof areas with different types of
roofing materials should not be joined
into a common collector pipe
Siphonic Design Rules cont'd…
• Roof areas with different pitches or on
different levels should not be drained
via a single down pipe
• Faulty project planning and general
ignorance can result in errors
Siphonic Design Rules cont'd…
• All troughs in a roof must be fitted with
at least one siphonic drain
• Maximum distance between drains is
65ft
=<65ft
Siphonic Design Rules cont'd…
• Length of the horizontal collector
pipe must not exceed 20 times the
height of the building
• Delta h dimension (the distance from
drain to horizontal collector) should be at
least 3 feet or the system needs to be
checked for priming.
• The variation between available
pressure and pressure loss in the
calculation of pressure loss for a flow
path can only amount to 1.47 psi
• Numerical value for the vacuum
pressure must not be less than px = 13 PSI
• Kinetic energy of the siphon pressure
must be converted so that the
velocity of flow is not higher than
8.2 ft/sec
=<8.2 ft/s
• To ensure the self-cleaning capacity
of the pipe system, a flow velocity of
at least
3 ft/sec is required
=> 3 ft/s
Siphonic System Questions and
Considerations
We will require building plans including roof layout and
building sections as a DWG file. Additionally the
below questions must be answered:
• Roof construction and measurements of
sections
• Ground plans for building sections
•
•
•
•
•
•
Rainfall data
Location of drains and down pipes
Type of pipe and drain
Details of other pipes and installations
Requests for rainwater harvesting
If overflow drains are required
Siphonic Estimate
• To do determine the number of
drains
1.Use the Zurn rainfall chart to select the number of
drain based on Square feet and rainfall data.
2. Select location of the drains on the roof
3 Select the location of the down pipe
4 As a rule, the length of the collector pipe cannot be
greater than 20 times the height of the building.
5 Maximum distance between siphonic drains is 65
ft.
6 Draw to scale and send to Zurn representative for
calculation.
7 Maximum 50,000 sq/ft per down pipe.
Siphonic Estimate
Siphonic System Specification and Installation
Siphonic Installation: Points to
Remember
• Install in accordance with industry
practice, governing codes and
regulations, and manufacturers’
instructions
• Siphonic drainage should be treated
as an engineered system
• Performance related to pipe
material, diameters, lengths,
elevations; and placement of fittings
• Contact Design Engineer if changes
are required
• Materials, fittings, and joining methods shall comply with ASPE Siphonic
Drainage Design Standard 45 in
Table 2.1
• Use fittings and components listed under applicable ASTM standard;
fittings shall be of the drainage, waste, and vent (DWV) type
• Manufacturers of siphonic roof drains
are required to test and certify their
products in accordance to ANSI/ASTM
112.6.9 Siphonic Roof Drains.
• Local plumbing and building code
requirements apply when selecting
conventional roof drainage materials
• ASPE publishes the Plumbing
Engineering and Design Standard,
Siphonic Roof Drainage (ASPE 45)
• Summary Benefits of Siphonic:
• No pitch requirement in piping to induce flow.
• Smaller pipe diameters get equal flow rates.
• Maximum Flow Rates of Zurn Siphonic: 2“ 147 GPM, 3“ 380 GPM, 4“
704 GPM.
• Vertical stack placement is flexible.
• Higher flow velocities help to clean pipes. No cleanouts necessary
in system.
• Green Benefits for siphonic construction
• More efficient than conventional drainage
• Use of recycled materials
The Zurn Siphonic Roof Drain System provides
green benefits to the building owner. Zurn
Siphonic Roof Drain design can help
buildings reduce energy consumption,
conserve water, reduce the depletion of
natural resources, and reduce construction
costs.
• Reduces site disturbance by collecting
multiple drain outlets below the roof instead
of underground.
• Reduces storm water runoff by reducing the
number of discharge points. Zurn Siphonic
Drains can discharge multiple roof drain
outlets into one vertical runoff pipe.
• Manufactured from post-consumer recycled
materials. All Zurn cast iron, plumbing, and
drainage products contain post-consumer
recycled materials.
• Provides an innovative design solution that
reduces the amount of drainage pipe,
reduces the diameter of the drainage pipe,
and provides more free space per square
footage in the building.
• Significant cost savings can be achieved by
using a well-planned Zurn Siphonic Drainage
design.