Checklist for Siphonic Roof Drainage
Every Pipework has to fulfil the following 10 rules:
1. Downpipe
2. Vertical connection pipe
3. Start-up requirement
4. Pressure loss Calculation
5. Vacuum (static pressure)
6. Minimum flow velocity
7. Flow velocity in the transition area
8. Drainage capacity of roof outlets
9. Distance between the roof outlets
10. Drainage capacity in the planning stage
Commandment 1: Downpipe
In Siphonic Roof Drainage the diameter of the downpipe shall be same or smaller than the adjacent collecting pipe.
![Siphonic Roof Drainage pipework in the transition area from the horizontal collecting pipe to the downpipe.](https://www.keidel-drainstar.com/wp-content/uploads/2023/01/RULE-1.jpg)
Commandment 2: Vertical connection pipe
VDI 3806 – The diameter of the vertical connection pipe may be larger or smaller than the diameter of the vertical roof outlet spigot.
BS 8490:2007 – The diameter of the vertical connection pipe must not be larger than the diameter of the vertical roof outlet spigot.
![Siphonic Roof Drainage pipework with roof outlet, vertical and horizontal connection pipe.](https://www.keidel-drainstar.com/wp-content/uploads/2023/01/RULE-1a-2.jpg)
BS 8490:2007.
Commandment 3: Start-Up Requirement
The calculation of the start-up requirement must be carried out at start-up height of < 100cm.
![Siphonic Roof Drainage pipework in the area of a vertical roof outlet connection.](https://www.keidel-drainstar.com/wp-content/uploads/2023/01/RULE-2-5.jpg)
Commandment 4: Pressure Loss Calculation
In the planning stage of a siphonic roof drainge pipework, the variation between available pressure and pressure loss must be +- 100mbar.
![Flow path table with calculation values from a siphonic roof drainage pipework.](https://www.keidel-drainstar.com/wp-content/uploads/2023/01/RULE-3.jpg)
Commandment 5: Vacuum (Static Pressure) in Siphonic Roof Drainage
In the hydraulic calculations, the vacuum pressure must not be less than -900mbar. The operating pressure limits of the pipe system must be taken into account.
![Table with calculation values Static Pressure of section parts of a Siphonic Roof Drainage pipeworks.](https://www.keidel-drainstar.com/wp-content/uploads/2023/01/RULE-4.jpg)
Commandment 6: Minimum flow velocity
Flow velocity of at least 0.7m/s is required according to VDI 3806!
![Table with calculation values flow velocity of section parts of a Siphonic Roof Drainage pipeworks.](https://www.keidel-drainstar.com/wp-content/uploads/2023/01/RULE-5.jpg)
Commadment 7: Velocity of flow in the transition area
In the transition area from a siphonic system to an open drainage system, the flow velocity must not be higher than 2.5m/s.
![Table with calculation values flow velocity of flow in the transition area in a Siphonic Roof Drainage pipeworks.](https://www.keidel-drainstar.com/wp-content/uploads/2023/01/RULE-6.jpg)
Commandment 8: The drainage capacity of the roof outlet
The drainage capacity of the roof outlet in Siphonic Roof Drainage must not be selected as greater than the maximum drainage capacity of the relevant roof outlet.
![Dialog with display of nominal discharge capacity of a siphonic roof outlet and table of calculation values per flow path in a siphonic roof drainage pipe.](https://www.keidel-drainstar.com/wp-content/uploads/2023/01/Rule-8-NEU.jpg)
Commandment 9: Distance between the roof outlets
The distance between the roof outlets in a shared drainage axis must not exceed 20 meters.
![Isometric drawing of a Siphonic Roof Drainage pipework to control the distances between the roof outlets.](https://www.keidel-drainstar.com/wp-content/uploads/2023/01/RULE-8.jpg)
Commandment 10: Drainage capacity in the planning stage
In the planning stage of Siphonic Roof Drainage pipework, the effective drainage capacity of all the outlets allocated to a roof surface or roof segment is not allowed to fall short of the nominal drainage required by the calculation.
![Anzeige Dialog der erforderlichen und der berechneten drainage capacity von einem Siphonic Roof Drainage pipework.](https://www.keidel-drainstar.com/wp-content/uploads/2023/01/RULE-9.jpg)
Closing words
At the end of this blog I would like to ask all designers to follow and apply these 10 commandments. It should be second nature to you, as it is to any airplane pilot. There are other important rules, tips and tricks that I will come back to in other blogs. The examples in this blog were created using Keidel’s DrainStar® Siphonic Calculator, the compact software for sizing siphonic roof drainage.
DISCLAIMER – This Information is based on German laws, standards, and regulations (rules). We shall give no guarantee that the information is suitable for use in other countries or that it is in accordance with the rules in place there. Nevertheless, we are unable to guarantee the correctness, completeness and up-to-dateness of the information and therefore exclude any liability in this respect. Subject to change without notice. © Keidel DrainStar GmbH. All rights reserved. V 2110