Things down the drain (Part 2)

By Benjamin Brits

Continuing the feature from the April issue, and having spoken with several plumbers in the industry, we aim to answer these questions around drainage.

Drainage is something that most people do not even think about yet it is vital, as drainage allows the removal of waste and wastewater, creating a safer and healthier environment for us to live in.Drainage is something that most people do not even think about yet it is vital, as drainage allows the removal of waste and wastewater, creating a safer and healthier environment for us to live in.


Concrete drainage pipes that have been laid at Heathrow Airport, UK.

What are the correct standards in terms of vents?

The answer in this case can also be found in SANS10400-P. The following are some important aspects that relate to the DTSR:

  • There must be a 100mm-diameter open vent pipe at the highest, furthest point of the drainage system of a building.
  • All branch drains longer than 6m shall have a vent pipe of at least 50mm in diameter. This is a minimum requirement.
  • The vent pipes shall rise beyond the roof and above all windows as detailed in SANS10400-P.
  • It is very important that a vent valve shall also be situated above the window and above the roof.
  • A two-way valve shall not be installed inside a building.


Why is the quality of materials important?

The basis of the NBR is health and safety, and quality directly relates to health and safety. It also relates to longevity (lifespan and durability) and it relates to operation, maintenance, and costs.

Inferior quality of materials can be dangerous and require more costly maintenance and may be a health threat. Low-quality piping has caused serious technical problems, costly replacements, and expansive water wastage. The SABS standards for materials and many other international standards are for good quality, safe, and economic installations.

When it comes to the installation and management of drainage, it is crucial to consider not only the obvious health risks, but when using products of a lower quality that do not last, the risk of human contact becomes greater, which leads to greater probability of health issues. This includes the risk of leaks contaminating potable water supply or boreholes, which not only affects a single point but can harm entire communities.

Better quality, or best quality, is important for a long-lasting system. The general lifespan of a commercial building is between 20 and 25 years and the quality of piping, fixtures, and equipment must be able to last for this period. Updated standard development requires piping to last as long as 50 years.


An HDPE drainage installation in a commercial building.


A typical drainage installation for a public restroom.

What is the correct preparation for pipe beddings and compaction?

SANS1200 contains the necessary information on this topic. There are a number of important elements, such as the following:

  • The ‘excavation’: The trench must not be over-excavated, deeper than the invert levels, and then backfilled with soil with no compaction.
  • The bottom of the trench must be the same density as the adjoining material and not be able to subside when water penetrates the trench later on, causing the pipe to subside, and therefore resulting in not being straight — which causes blockages.
  • If necessary, the bottom of the trench must be compacted.The bedding of the piping is clearly specified in the standard and other pipe manufacturers’ manuals. However, the best pipe bedding is river sand and normally at least 100mm thick under the barrel of the pipe and around to the middle of the pipe.
  • Once the pipe is pressure tested, then the pipe is covered with river sand (in the absence of river sand, a granular material free from stone can be used as specified in the standard) to 300mm above the top of the pipe. This cover of 300mm over the pipe can be lightly compacted.
  • Once the pipe is covered with the 300mm thick cover, then the rest of the backfilling can take place, in layers of about 150mm thick, and each layer is to be compacted to the same density as the adjacent soil.
  • Always refer to the engineer’s specifications (if the design was done by an engineer), as well as the pipe manufacturer’s specifications, as these may vary depending on application.
  • The above mentioned is relevant for areas where there is no traffic, and in traffic-bearing installations, the pipe must be protected with a concrete slab over the 300mm cover.


What will happen with new technology like no-flow or low-flow devices?

These types of fixtures are still not officially approved and therefore will not be specified in SANS10400-P, but it is important for the future of drainage to find solutions for our water shortages, as well as other alternatives.

One solution may be the adaptation and development of systems to use greywater, and low-flow toilets and urinals, which will also significantly alter the design and workings of a drainage system, as additional elements would need to be specified and implemented, such as treatment facilities per property. There is a new SANS document forthcoming that will address water conservation, which includes lesser flow rates for fixtures.

An interesting concept was discussed at the end of last year between the Water Research Commission and the Department of Science and Technology as they evaluate decentralised wastewater treatment units even for residential units. This would essentially mean that sewage would be treated at the source rather than conveying it to wastewater treatment plants that are already unable to handle current volumes.


What elements does the inspector look at and why does the installation typically fail?

It is both a regulation and a legal requirement that a building inspector must/shall inspect a drain before it is closed and be present when the pipe is pressure tested. Only on the final inspection will he or she issue the certificate of compliance (CoC).

The building inspector is supposed to inspect the total installation to ensure it complies with the deem-to-satisfy rules if it is not a rational design. If it is a rational design, then the engineer is responsible for approval.

It is important to note that the building inspector does not inspect the water installation; he or she only has to inspect the hot-water generation and the elements pertaining to SANS10400-XA.

The most common problems are:

  • Incorrect gradients of the discharge pipes and drain pipes.
  • Water pipes that fail because of a leak.
  • Hot-water systems that are incorrectly designed and incorrectly installed.
  • Contractors who appoint unqualified plumbers to do the work and then completely ignore the design drawings, with the result of a hugely and costly failed installation.


What elements are involved in the design approvals?

The only design drawings that are relevant or required for approval, are the drawings on the sanitary drainage system. In SANS10400-A, all the information required on the drainage drawings is stipulated. The important elements are:

  • The site plan
  • The building’s floor plan
  • The relevant elevations
  • The relevant sections.

The drainage piping must be indicated on all the floors and sections, the elevations with all the piping and piping elements with pipe sizes must be indicated, and ventilation piping with all the gradients in all the prescribed colours must also be indicated. 

The design must only be done by a person who is termed ‘competent’ by having the technical and theoretical qualification, experience, and understanding of all of the elements of a drainage system.



With drainage, if it is done correctly, everything flows as it should, but when done incorrectly, it has a negative impact that results in major health risks. This feature only covered the basic principles of a regular building and has not even touched on hotels, high-rise offices, or specialist facilities. If you would like any further information or more detail on any aspects of this particular feature, please get in touch by sending an email to This email address is being protected from spambots. You need JavaScript enabled to view it.. 


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