CASE STUDY FOR SITA DSS SIPHONIC
DRAINAGE SYSTEM AT HOE VALLEY
SCHOOL, WOKING
This new school sits on 4 acres of a 22 acre site and provides
modern, purpose built facilities for students needs for a 21st century
education. This is why careful consideration was given in choosing
the right drainage solution and as such the Sita Bauelemente GmbH
DSS Siphonic Drainage System was chosen.
Working in close cooperation with the our specialist contractor
IPS Group, who were responsible for the installation. This project
meets all the requirements to be able to protect the building and its
contents for the designed building life of 20 years and more.
DESIGN
For quality control all siphonic drainage systems are designed by
Sita’s fully trained technical consultants. That way we can assure that
design meets with all the associated British standards and the whole
design can be traced right back to original designer.
The first operation in calculating the effective rainwater run-off from
the roof was to calculate the rainfall intensity. In UK practice the RFI is
derived from a series of intensity – location graphs in national annex
NB of BS EN12056-3:2000. This detailed procedure takes a 2 minute,
5 year rainfall depth for the chosen location, then by means of
growth factor charts, converts this into 2 minute storm of the chosen
return period.
The return period is based on the building life, which in this case was
20 years. It is then multiplied by the factor of safety, which is typically
1.5 (CAT 2) or 4.5 (CAT 3), depending on the level of protection the
building requires.
Due to the nature of this project a CAT 3 category of risk was chosen
for the main drainage system, with a gravity fed emergency drainage
system as back up designed to drain 50% of the overall rainfall
intensity.
The RFI was calculated at 0.059l/s/m2 for the main drainage and the
information, along with the effective roof areas, was then used to
calculate the pipework configuration for the main drainage, using well
established hydraulic principles in compliance with BS8490:2007
and BS EN12056:3-2000, which gives accurate calculated results.
INSTALLATION - NO SPACE WASTED
One of the biggest challengers when installing siphonic drainage
systems is coordination with other services within the building. On a
building such as this there was limited space within the ceiling void
to accommodate all services and therefore careful consideration was
given to ensure that no clashes occurred.
Due to the limited ceiling void is was particularly important to pick
the right system. The Sita siphonic drainage system is suspended
from the troughs of the structural metal decking, at 0% gradient by
use of metal deck hangers. This provided a secure fixing point for
A total of 21no DSS Profi siphonic outlets were used for the main
drainage, with a further 13no SitaTrendy outlets providing gravity
fed emergency drainage to the building. To be confident that a
secure connection between Sita outlets and the waterproofing
layer is achieved Sita’s outlets came with a fully bonded membrane
connection flange using the same waterproofing material as the roof.
Due to rigorous in house testing methods Sita offer a standard 10
year guarantee on all roof drainage products. Sita outlets are also
regularly 3rd party tested and monitored by TUV Rheinland, which
confirms that they are manufactured in accordance with DIN 1253-
2:2015-03, that way you can be sure you are receiving a quality
product.
SITA SOLVES PROBLEMS
Sita’s calculation service is an elementary aid and a great starting point
for your project. On the basis of your specifications, Sita calculates
precisely how the siphonic system – covering the rainwater outlet,
pipe and fastening system – has to be designed for the particular
location and individual building type. Even if the requirements are
very complex.
Using a Sita siphonic system means that on average 70% less
downpipes are required, when compared to a gravity system. This
not only saves space within the building, but also means that there
is almost no need for underground pipelines and their associated
groundworks.
That coupled with the expert knowledge of the installation provided
by IPS Group means, that when specifying Sita Bauelemente GmbH
you can confident you are receiving the highest quality products.
For more information visit www.sita-bauelemente.de
IPS had to work with the M & E sub-contractors and other trades
and work in a co-ordinated manor to ensure all parties could work
together in a structured and efficient way.
the Sita DSS rail system that supports the HDPE pipework. This is an
important architectural benefit because the lack of gradient meant it
took up less space.