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BEAM P
LUS FOR
E
XISTING
B
UILDINGS
I
NDOOR
E
NVIRONMENTAL
Q
UALITY
(I
EQ
)
V
ERSION
1.2
I
EQ
2 P
LUMBING AND
D
RAINAGE
Copyright © 2012 BEAM Society Limited. All rights reserved.
Page 112
multi-level drainage systems. The main ways that air passes a trap are:
system pressure variations cause air-entrained bubbles to pass
through the water seal; and/or
complete or partial trap seal loss.
Unless water is replenished, from time to time, by the building users or
through discharge of waste water cross-contamination is likely. Viruses
can enter indoor spaces through water traps if water seals are dried out
or contaminated, or there is leakage in pipework. Under working and test
conditions traps should retain a minimum seal of 25mm of water or
equivalent.
I
NSTALLATIONS
Leaky joints and broken drainage pipes are the result of lack of regular
inspection and maintenance. Pipework needs to be as accessible as
possible in order to carry out such work, and building management
should be provided with means for regular inspection, maintenance and
repair of building drainage systems.
V
ENTILATION
Where mechanical ventilation in the form of an extractor fan is provided,
such as in bathrooms and lavatories, care should be taken to ensure that
water seals are intact and operate according to the design intent [2].
Consideration should be given to the quality and quantity of air intake,
air-flow path and fan capacity.
The Environmental Health Team of the World Health Organisation
(WHO) has advised that the optimum volume for bathroom ventilation is
2 cfm/sq ft (10.2 l/s per sq. metre). WHO is of the view that a larger
volume does not add much on the comfort side and has the hidden risk
of building up negative pressure. Designers are advised to provide an
opening to bathrooms and lavatories for make-up air, such as an
undercut to the door or an opening with a louvre at the door or wall, in
order to minimise the build-up of negative pressure where an extractor
fan is used for ventilation. The airflow path created should avoid
circuiting of the ingress and exhaust air.
2
Buildings Department. Practice Note for Authorized Persons, Registered Structural Engineers and Registered
Geotechnical Engineers, PNAP No. ADV-25 Extractor Fans in Bathrooms and Lavatories in Domestic Buildings.
http://www.bd.gov.hk/english/documents/pnap/ADV/ADV025.pdf