Deem-to-satisfy rules and rational design

At Vollie’s birthday breakfast (back, from left): Colin Scott, David McIver, Fabio Conte, Dean Cane, Paulus Damen, Sarel Odendaal. Front (from left): Anthony Giurichic, Vollie Brink, Eddie Pretorius.

By Vollie Brink

What is the difference between deem-to-satisfy rules and rational design? And why is it important for you to know the difference?

We are working on South African National Standard (SANS) 10400-P to revise it and to ‘modernise’ it, but above all to make it relevant for today and to make it easy to understand and apply.

When we go back in to the history of the National Building Regulations (NBR) the first objective was to have national regulations, because in the days before 1977, every little town had its own home grown regulations. I remember that Bloemhof had a regulation that you are not allowed to crack a whip in the main street, and the main street of Bloemhof was made wide enough so that you could turn an ox wagon around in it.

Many other towns had their own peculiar building regulations and it was difficult to do a design before you went to the building inspector to find out what their regulations were. And the building inspector could make and change ‘his’ regulations as he wished. The result was that there were no common standards and what was allowed in one town was not allowed in another town.

The NBR of 1977 brought an end to this chaos and made the life of the designer and plumber much easier.

When the national regulations were presented to the public there was a large meeting held at the SABS and one building inspector of a large city stood up and said, “I will still apply my rules.” This gentleman had a broad belt around his waist, as well as trouser suspenders to make sure his pants stayed up regardless, and that was how he managed his office.

There was much confusion about how to interpret these new regulations and it led to many arguments.

My company allowed me to spend time on studying each item and interpret it in terms of a full set of diagrammatic drawings which were approved by the SABS, and they were requested and used by building inspectors all over the country, and as far as Windhoek. These diagrammatic drawings settled many disputes, explaining adequately what was written in SANS10400-P, and were used for many years.

This lack of a boundary has caused many serious disputes, review board cases and animosity.

You must be aware that the deem-to-satisfy-rules (DTSR) in SANS 10400-P were meant to be used as a recipe or a method to comply with the performance requirements of the regulations. The DTSRs were meant to be used by anybody so that you don’t need and engineer to design non-complicated engineering services. This is a crucial element of the NBR, and over the years this has been forgotten.

There was a critical element that was never addressed in the original NBR or in the later revisions, and so there was, and still is, no clear descriptive boundary between what DTSR is and what is supposed to be rational design.

The only direct indication is that if the building control officer deems it necessary, the design must be rational design. Second, the owner has the right to choose the design to be a rational design, but otherwise there is no clear-cut definition of a boundary for the DTSRs in SANS 10400-A or SANS 10400-P. This lack of a boundary has caused many serious disputes, review board cases and animosity.

In the first instance, SANS10400-P refers to two types of buildings: residential buildings and office buildings, and there are no specific rules for the design of large footprint buildings such as hospitals, shopping centres and the like.

Another very important indication is what you are not allowed to do, such as the following:

  1. You are not allowed to have a bend under a floor that is situated underneath a floor.
  2. You are not allowed to change direction under such a floor.
  3. You are not allowed to change gradient under such a floor.
  4. You are not allowed to have connections between pipes under such a floor.
  5. You are not allowed to have access such as a manhole or inspection chamber in a building.

These five rules are basically the most important indication of a boundary between a DTSR design and a rational design as per the present SANS10400-P. The implication is that with the DTSR you have to keep the drainage pipe above floor and discharge it directly to a stack pipe, stub-stack or gulley.

The anomaly is that the present SANS10400-P has rules for high-rise buildings such as residential and office buildings that really require a rational design by a competent person, which was indicted to be a registered engineer, technologist or technician. The working group has grappled with this issue of a boundary where the DTSR ends, where the rational design should begin, and the competency required in terms of design.

SANS 10400-A and P require a competent person to do a rational design, which then implies that the DTSR design does not need a competent person, but it requires the plumber to be competent. The question now is how can the above-mentioned five items be resolved in a rational design?

It is important that these five items refer to piping that is to be designed and installed to be buried under the ground, under a floor or structure, and which is covered by a concrete floor and therefore not accessible once it is installed.

Vollie recently celebrated his 80th birthday, and
Plumbing Africa would like to wish him all the best. An industry stalwart himself, Vollie marked the occasion by sharing a breakfast with other industry stalwarts.


It is a fact that the situation in a hospital or large shopping centre or other large building with a large footprint will require internal piping which will be situated under a floor and buried in the ground, therefore it will need an innovative rational design solution. The question is, what is the solution?

The most important thing is that all bends must be long radius or at least a bend made up of two 45 degree bends with a length of piping of 1m in-between forming a radius of not less than r=600.

All junctions under such a floor must also be done with large radius connections and rodding eyes must be provided in ducts where possible, but the piping must be serviceable from above the floor and floor drains and stub-stacks that terminate on floor level is a handy solution and works well. This floor level stub-stack has been used in many buildings over many years.

The stub-stack is an excellent solution for many buildings from housing to office blocks and shopping centres and hospitals and, what I call a floor-stub-stack is merely a stub-stack that is terminated at floor level with connections level with the floor. Any fixture can be connected to it and it can also be used as a connection for a stack pipe to collect drainage fromm a floor above the ground level such as the case of a mezzanine.

There are many other innovative solutions such as an overflow fixture to prevent back flow into a building, which prevents unpleasant situations inside a building and allows the unpleasant situation to happen outside instead.

This overflow fixture consists of a simple junction with a cap on top that can pop open when there is a blockage either up or downstream and discharge the soil outside the building. This overflow fixture is very handy, particularly in the case of hospitals, to prevent back flow into the waste water system which then pops out of the shower, bath and floor drain – a clear health risk.

I have proposed that we develop a set of standard details that everybody in the industry can use, and so develop higher standards for the industry.

Pin It
PA PD TP PO SA Plumbers Handbook Logo Plumbing newsletter

Talk to us


Connect with us

Keep in touch via your favourite social media