DESIGN: DEAR MR PLUMBER
21
Notes on a drawing: Part 1
By Vollie Brink
In the past, I have been asked to review the design drawings of
other, shall I just say ‘designers’, and to comment on the design.
When I review the drawings of other people then it
is important, not to see if it complies with my view,
but if it complies with the regulations. This is Part 1
of a two-part series.
The regulations as stated in the National Building
Regulations (NBR), which you will find in the relevant
Addendums, and which are the most important part of
the NBR, describe ‘how the system must perform’, and
it is basically the specifications for the designed and
constructed system.
However, it is extremely important that these specifications
for the performance be clearly built into the design and the
design must comply with the agreement with the owner /
developer, which in most cases is the PROCSA agreement,
which stipulate all the phases of design and construction
in detail.
Any design must comprise of detailed drawings and
‘specific detailed specifications’ – and this is where I find
problems. Many ‘designers’ cover themselves by means
of ‘notes’ on the drawings, such as: ‘The drainage system
shall comply with SANS 10400-P’ or ‘The domestic water
system shall comply with SANS 10252-1’. However, SANS
10400-P and SANS 10252-1 consist of many options,
raising the question of which option the plumber must
comply with?
I encountered someone who had just indicated by means
of a note that the gradient must be 1:60 and the actual
gradient installed was 1:1000 and the reason for it was
that the space in the building only allowed this 1:1000
gradient. This meant that the designer did not actually
check if the pipe can be installed as per the ‘note’ on the
drawing. If an appropriate Quality Assurance (QA) system
was applied, then the abovementioned problem should
have been found and rectified before the building was
occupied. However, the problem should have been found
earlier by means of a ‘Design QA’ system by the designer.
It seems the designer and the plumber lack training in QA.
SANS 10252-1 is inherently a Design Manual with
some installation rules. If the designer puts a ‘note’ on
the drawing that the installation must comply with this
document, does that mean the plumber must do the
design? In the case of this document we deliberately
designed the tables with ‘ranges’ of ‘flow rates’ and
‘volumes’ and pressures, and more.
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 well-
earned retirement.
These ‘ranges’ were devised so as to force the designer
to select a flow rate and pressure and volume to suit the
specific project. We also deliberately used litres per minute
and not litres per second because litres per minute is
full figures and not figures with decimals and easier to
calculate without a calculator. PA
There is a Table for gradients for discharge pipes inside
buildings and there is a Table for drains which must
connect the building with the municipal sewer. These
gradients of the piping inside and outside the buildings
must be carefully calculated to convey the effluent from the
fixtures in the building, through the building, through the
drains outside the building up to the sewer connection and
even further down to the sewage treatment plant, which
as mostly kilometres away from the property, and if there
is not enough gradient and water the municipal system
cannot function.
By the way, all the Tables for sizing of the piping and
gradients in SANS 10400-P and SANS 10252-2, are
‘wrong’. All the invert levels, gradients, dimensions and
access positions must all be correctly indicated on the
design drawings, and you cannot get away with a note.
March 2020 Volume 26 I Number 01
You cannot get away with a ‘note’ on the drawing that all
pipes must have a fall of 1 in 60. You must calculate and
indicate the exact positions and exact invert levels on the
drawings and it must relate to the levels of the building or
to a peg on the site with a specific level. In one instance
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