DESIGN: DEAR MR PLUMBER
25
Access to and into: Part 2
By
Vollie Brink
There are three important elements of the design of Building
Water Services (BWS): the sanitary drainage system, the domestic
water system and the fire water system of a building, positioned
either inside, outside or beneath the building. This is Part 2 of a
two-part series.
The question is, what is the solution? (Continued)
The only solution for all piping under the floor in ground is
the following:
• The design can only be a rational design.
• The waste-water pipe system and the soil-water pipe
system must be completely separate systems.
• All piping (wastewater and soilwater) under the
floor, in the ground, must be a minimum of 100mm
diameter.
• All piping must have access into the piping from above
to insert rodding equipment and camera equipment
for rodding and to inspect the total internal surfaces of
the piping.
• Access entry points must be provided at least 25m
apart, and where necessary, for rodding and camera
inspections. Access entry points must preferably be in
ducts which are 25m apart and must be rodding eyes
or cleaning eyes, which are 150mm above the height
of a WC pan.
• The testing of a piping system must include the
normal pressure test but also a camera inspection
and a smoke test and the actual invert levels shall be
surveyed by a competent person who is able to carry
out a survey and produce a set of ‘as-built’ drawings.
• Backflow/overflow facilities shall be provided at each
position where the drainage systems exit the building
and must be shown on the drawings.
• The drainage piping may have less fall than 1/60 from
where it exits the building, but it must be a hydraulic
designed system and designed as a ‘sewer’ and not as
a ‘drain’ as per SANS10400-P.
• Refer to SANS 1200 / 2001.
• Manholes are preferable for the external sewer.
• The ‘benching’ of manholes must be correctly and
carefully constructed as per the design detail drawing.
The rational design of these services requires intimate
knowledge of the hydraulic dynamic theory and pipe systems
and pipe materials, and senior competent plumbing artisans.
Water piping under a ground floor in-ground:
• If the domestic or fire water piping systems are
required to be situated under the ground floor in
ground, then it must also be a rational design by a
competent engineer.
• Water piping must not be installed and cast directly in
the concrete floor. It must be installed in pipe sleeves
as required in SANS 10252-1.
• The piping must be installed in sleeves in such a
manner to allow the piping to be removed to be fixed if
it leaks or is to be replaced when necessary.
Redundancy:
Due to the ever-escalating cost of developments, there
is much pressure on designers to cut costs, leading to
important design principles such as appropriate ‘redundancy’
not being provided for to save capital cost. However, in the
end this can cause serious operational and maintenance
costs and serious discomfort for the inhabitants.
A typical example is where you have only a single pump in
a pump-set. When this one pump fails, the total system fails
and this can be a serious discomfort for the inhabitants of
the building, specifically when it is a hotel or hospital.
Another example is where you have only one supply
pipeline from the hot water generation plant to the main
building where the water is reticulated, and the same goes
for the cold-water supply. If there is a problem, such as a
leak on these supply lines, then the system – such as in a
hospital or hotel – can be a serious matter. This could be
more expensive than to have provided redundancy in the
first place.
It is the duty of the designer to make the developer aware of
the consequences of not providing appropriate redundancy.
We had a saying in the office: If you have only one pump and
something goes wrong, then you have 100% nothing. But if
you have two pumps and something goes wrong, then you
have only 50% nothing! PA
Vollie Brink is one of the
industry’s longest-serving
wet services engineers.
He continues to serve on
SABS committees and
has been involved in the
Green Building Council’s
Green Star rating system.
Brink continues to consult
for various organisations
while enjoying a wellearned
retirement.
August 2020 Volume 26 I Number 06
www.plumbingafrica.co.za