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Drainage
While standing water has no effect on Sarnafil membranes, it is always good practice to try and ensure that a roof drains as efficiently as possible.
This prevents the accumulation of airborne dirt and dust and, with the increasing building density, improves the aesthetics of the roof.
To assist the designer in the provision of a suitable gravity drainage system and in accordance with BS EN 12056 – 3: 2000 ‘Gravity drainage Systems inside buildings. Part 3 Roof drainage, layout and calculation’ and the Building Regulations Approved document Part H, Sarnafil offer a drainage calculation service based on our standard rainwater outlet range.
This has been tested to BS EN 1253 : 2000, to enable the accurate provision of rainwater calculations. For siphonic drainage systems, Sarnafil can provide whole system solutions with the assistance of Branded Product Partner Dallmer Ltd.
Whilst a green roof will retain approximately 50% + of the incident rainfall and delay the discharge, reducing the number of rainwater outlets on a project requires a number of factors to be carefully considered. These include, but are not limited to:
- The roof pitch
- The green roof system type
- Drainage onto the roof from higher levels
- The type of growing medium
- The commitment to keep the roof in place and greened for the life of the building
In all instances, where a reduction in rainwater outlets is utilised, tell-tales or overflows should be installed to prevent problems in the event of the system reaching 100% saturation.
All of the following information is required to enable Sarnafil to make drainage calculations:
- Can water safely overflow from the roof?
- If yes, the type and size of overflows
- Limitation on number of outlets
- Risk factor in accordance with BS EN 12056 – 3:2000
- Category of building use e.g. hospital operating theatre, computer/comms centre, storage for irreplaceable art works, or production line where interruption will be very costly.
- Sketch plan of the roof showing preferred outlet locations and plan areas marked-up on the drawing, including any vertical wall areas that could drain onto the roof.
Request drainage calculation
© 2006 Sarnafil Ltd. Legal Disclaimer
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