To protect a building in Dar es Salaam from heavy rain and flooding, raise the ground floor above the expected flood level, slope the ground and paving away from the building, build drains that can carry heavy downpours, and make sure the roof, gutters and walls shed water quickly. Good drainage is far cheaper to build at the start than repairs after a flood. The measures below work for both new buildings and existing ones.
Why is flooding a risk in Dar es Salaam?
Dar es Salaam is low-lying and coastal, with many areas close to rivers and valleys such as the Msimbazi. During the long rains (masika, roughly March to May) and the short rains (vuli, roughly October to December), heavy downpours can overwhelm drains, especially where plots have been raised or paved around them. Water that cannot run off collects around buildings and enters floors and walls.
How do you choose a safe site and floor level?
- Ask about past floods. Neighbours and local leaders often know where water collects.
- Check the land level compared to the road and neighbouring plots.
- Raise the plinth. Set the ground floor level comfortably above the highest known water level, with steps at the entrances.
- Avoid building in valleys or river reserves, which are also legally restricted.
The Tanzania Meteorological Authority publishes seasonal rainfall outlooks that help you plan construction around the rains.
What drainage does a building need?
Water must leave the plot quickly and in a controlled way:
- Slope the ground away from the building on all sides.
- Build a concrete apron around the walls so water does not soak into the foundation.
- Install open or covered drains along the boundaries, sized for heavy storms.
- Connect drains to a safe outlet, such as a public drain, soakaway or storage tank.
- Keep drains clean, especially before the rainy season.
How do you protect the walls and floors?
| Measure | What it does |
|---|---|
| Damp proof course (DPC) | Stops ground moisture rising into the walls |
| Damp proof membrane under slab | Keeps moisture out of the ground floor |
| Water-resistant plaster at the base | Protects the lower wall from splashing |
| Raised door thresholds | Keep surface water out of rooms |
| Tiled or sealed floors | Make cleaning easier if water enters |
How do you make the roof handle heavy rain?
The roof collects a large volume of water in a short time. Use gutters and downpipes sized for heavy downpours, with downpipes that discharge into drains and away from the walls. Wide roof overhangs protect walls from driving rain. Flat concrete roofs need a proper fall to outlets and good waterproofing; see our guide on waterproofing roofs and walls.
Can rainwater be collected instead of wasted?
Yes. Rainwater harvesting tanks connected to the gutters reduce the water reaching the ground during storms and give you a useful supply for cleaning and gardening.
What should you do for an existing building that floods?
- Map where water enters and where it collects.
- Improve the slope and add an apron and drains.
- Raise thresholds and seal gaps at doors.
- Repair cracks and damp walls only after fixing the water source.
- If flooding is severe, ask an engineer about raising floor levels or adding a retaining wall.
Frequently asked questions
How high should the ground floor be above the ground?
It depends on the site. On flood-prone plots, an engineer sets the floor level above the highest expected water level, often with several steps up to the entrance.
Does flooding damage foundations?
Yes. Repeated wetting softens the soil, and on clay soils it causes swelling and shrinking that cracks walls. Read about black cotton soil foundations.
Can I build on a plot that floods?
Sometimes, with the right engineering, such as raised floors and proper drainage. But plots in river valleys or reserves should be avoided.
What is the cheapest way to reduce flooding around a house?
Correct ground slopes, a concrete apron and clean, well-sized drains are the most cost-effective measures.
Build for the rainy season
Vika Construction designs site levels, drainage and foundations that suit Dar es Salaam's rains. See our civil works services or contact us.
