DESIGN: DEAR MR PLUMBER
drain inspection: the pipe is laid on the bedding (still
uncovered) and a pressure test is done. The problem
with this test is that when the inspector walks away after
the inspection, the plumber will cover the piping and
then, in many cases, the pipe is damaged by stones and
other sharp material.
The process only consists of a visual inspection — to see
if the pipe is laid straight on the bedding — and the air
test. The inspector does not test the gradient. He or she
does not check the invert levels, because in most cases
the invert levels are not indicated on the drawings. The
gradient is just indicated as 1 in 60 — and the actual
gradient is found to be nothing but 1 in 60. When the
two actual invert levels are connected, you find the actual
gradient works out to be 1 in 1 000.
I have seen drainage with a fall of 1:1 000, inspected
and signed off by the building inspector and, therefore,
also approved.
The inspections which the “competent engineer” require
are the following:
1. The correct setting out as per the design drawing.
2. Check the pipe and the materials.
3. The corrected excavation levels (make sure the
4.
5.
6.
7.
8.
9.
10.
11.
37
contractor did not over-excavate and fill the trench
with loose material up to the correct invert level).
The pipe bedding material.
The pipe as laid.
Pressure test of the open pipe.
Cover of the pipe with the first layer as specified.
Pressure test of the covered pipe (most important test).
The backfilling as specified.
The “as-built” drawings.
The CoC from the contractor.
When it comes to a building drainage system,
SANS 10400-P is the only legal document in terms of
the NBR, but it seems as if the SABS is bent on collecting
documents that are extremely confusing, as they clash
with the SA documents. The following documents all talk
about drainage:
• SANS 52056-1:2010
• EN 12056-1:2000
• South African National Standard
• Gravity drainage systems inside buildings – Part 1:
General and performance requirements.
There are five more such documents. Why and what for? If
litigation is required, then SANS 10400-P will be the only
document relevant and then only the regulations from P1
to P7, or am I wrong? PA
When it comes
to a building
drainage
system,
SANS 10400-P
is the only legal
document
in terms of
the NBR.
January 2018 Volume 23 I Number 11