A Joburg afternoon thunderstorm can dump 30 mm of rain in 20 minutes. On an average 400 m² Sandton roof, that's 12,000 litres of water — all of which has to go somewhere in a hurry. If your stormwater drainage isn't sized right and isn't clear, that water ends up against your foundations, in the garage, or in a flooded driveway.
Why stormwater is a plumbing problem
Foul drainage (toilets, basins, kitchen) and stormwater drainage (roof, paving, driveway) are separate systems by law. They shouldn't connect. But in older Joburg homes we constantly find the two illegally linked, which overloads the foul line in heavy rain and causes sewage to back up into bathrooms during a storm. A proper drainage survey separates and fixes this.
The four things that fail
- Blocked gutters and downpipes — water cascades over the eaves onto the wall heads.
- Downpipes discharging into flowerbeds — water saturates the soil right against the foundation.
- Stormwater gullies blocked with sand, leaves and paving silt — driveway floods, water enters the garage.
- Undersized stormwater main — common in 1970s homes that have since added a pool, patio roof and extra paving.
What a proper fix looks like
- Seamless aluminium gutters with the right fall (1:300) and proper outlet count.
- Downpipes piped underground in 110 mm PVC to a stormwater main, not dumped on the lawn.
- Channel drains at garage doors and gate openings, draining to the stormwater main.
- Catch pits with leaf baskets that can be cleaned without lifting paving.
- A discharge point to the street kerb that's compliant with Johannesburg Water bylaws.
French drains: when and where
French drains (a perforated pipe in a stone-filled trench) are useful where you can't easily get to a kerb discharge — typical for back gardens that slope into the house. They work brilliantly on Joburg's sandy soils but block within 3 years on heavy clay if installed without a geotextile sock. We design and install both gravity French drains and pumped sumps for low-lying garden levels.
Cost expectations
- Full gutter and downpipe clean: R950 – R1,800
- Stormwater gully and main jet: R1,400 – R2,800
- New 110 mm stormwater main to kerb (per metre, trenched): R650 – R950
- 10 m French drain with geotextile and 19 mm stone: R8,500 – R14,000
Standing water around the house after a storm? Phone 082 886 9119 for a free on-site drainage assessment in Sandton, Midrand and Fourways.