Part P of SANS 10400 sets the deemed-to-satisfy rules for drainage: how to size and lay soil and waste pipes, the gradients drains must fall at, where access (rodding eyes) must go, and the rules for septic tanks, conservancy tanks and French drains where there is no municipal sewer. SANS stands for South African National Standard, the standard the National Building Regulations (the NBR, under the National Building Regulations and Building Standards Act of 1977) call up. Deemed-to-satisfy means the prescriptive route: follow the published rules and you are deemed to comply without a separate calculation. Part P is read alongside SANS 10252-2 for drainage and SANS 10252-1 for water supply.
The numbers below come from public summaries and archived copies of the paywalled SABS text (SABS is the South African Bureau of Standards) and the gazetted regulations. Treat them as plain-English orientation, not a definitive spec, and confirm the exact current values with your local authority and the SABS SANS 10400-P text before you build or submit plans.
What this Part covers
SANS 10400-P (the brief references the 2010 edition, 3) covers waste and soil pipe sizing, drain gradients, access for rodding, traps and gullies, ventilation of soil pipes, and on-site sewage handling where the stand is not connected to a municipal sewer. That last group, septic tanks, conservancy tanks and French drains, is the part most often got wrong on rural and peri-urban stands.
A drainage installation drawing forms part of the building plans, showing pipe sizes, gradients, rodding eyes, gully positions and any septic or conservancy tank detail. The local authority assesses it at plan approval and inspects the pipework before it is covered.
Key requirements (plain English)
Keep the caveat above in mind: these are orientation figures from public summaries and archived copies of the paywalled SABS text, so confirm the current values with the SABS Part P text and your local authority before building.
- Toilet pan connection. The WC connector must fall toward the soil pipe at a gradient of at least 1:40.
- Pipe joints. Joints must stay watertight at an internal pressure of 50 kPa and resist external water pressure of 30 kPa.
- Drain size and gradient. The minimum nominal drain diameter is 100 mm. Exact sizing comes from the hydraulic loading (fixture unit) tables in the standard. As a guide from the brief, a single WC on a 100 mm drain should fall no flatter than 1:40 for low flows under 1 litre per second; where peak flow is over 1 litre per second with at least one WC connected, a 100 mm pipe may be laid at 1:80.
- Rodding eyes (access points). Provide a rodding eye at every change of direction greater than 45 degrees, within 1,5 m of the connection to a sewer, septic tank or conservancy tank, at the highest point of the drain, and at intervals not exceeding 25 m measured along the drain.
- Traps. Every fixture must discharge through a trap with a water seal of at least 25 mm. A food waste disposal unit needs a P-trap with at least a 75 mm seal.
- Gullies. All waste water from outside a building (yard, patio) must pass through a trapped gully before it enters the drain.
- Ventilation. Discharge stacks must vent to open air at their highest point. Where the self-siphoning criteria in the standard are not met, trap vents are required.
For on-site sewage where there is no municipal sewer:
- Septic tanks. Minimum capacity is about 1,5 cubic metres for a dwelling house or unit and about 5,1 cubic metres for other buildings, retaining sewage for one day (dwelling) or three days (other). Site the tank at least 2,0 m from any boundary or structure. It must be liquid-tight, vented above eaves level, and easy to clear, and its effluent must discharge to a French drain.
- French drains (soakaways). Keep them at least 3 m from any building or boundary, no deeper than 1,8 m, and only where a percolation test gives a result of 30 minutes or less. They are sized from flow rate, application rate, width and height, and include an inspection pipe.
- Conservancy tanks. Capacity is set by the local authority. The tank must be liquid-tight, accessible for a vacuum tanker, and sited near the driveway.
When you need a competent person or plan approval
A competent person is someone qualified by education, training and experience, registered in their field. For drainage the law refers to a Competent Person (Sanitation): a registered Professional Engineer or Engineering Technologist with a civil or mechanical qualification and demonstrated sanitation experience.
You need rational design by a Competent Person (Sanitation) for any installation that does not meet the deemed-to-satisfy rules. Rational design means an engineered design and calculation in place of the prescriptive route. Examples from the brief include systems serving more than 10 dwelling units, commercial kitchens, industrial effluent, and pumped drainage. Day-to-day domestic drainage that stays inside the deemed-to-satisfy rules is installed by a registered plumber (trained plumber, minimum NQF Level 3 in construction plumbing) and approved through the normal plan process.
Common mistakes
- Missing or buried rodding eyes. No access within 25 m along the drain, or an access cover under permanent finishes, both fail inspection.
- Gradient too flat. Laying a 100 mm drain flatter than 1:40 where the flow does not justify the 1:80 option.
- Septic tank too close. Sited under 2,0 m from a boundary or structure.
- No percolation test. A French drain built in clay where the percolation time is over 30 minutes will clog and fail.
- Untrapped yard gully. Outside waste water running straight into the drain with no trapped gully.
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