Floods reveal hidden structural flaws in Kenya’s real estate

Prof Siphila Wanjiku, Dean of the Faculty of Engineering at the University of Nairobi, says the intensity and persistence of the rains are pushing buildings beyond what they were designed to handle.

“These buildings are supposed to be rigid whether it's wet or not, because the foundation is meant to be strong from the ground. Even when there is flooding, the water is expected to wet the wall, but naturally, the wall should dry,” she says.

She explains that prolonged exposure to water compromises both the visible parts of a building and its structural integrity. When water penetrates walls and foundations, it can cause long-term deterioration, making buildings unsafe even after the floods subside.

Once water seeps through construction materials, especially in poorly built or unprotected structures, it weakens the bonds within walls and can lead to gradual failure.

“The signs of irreversible structural damage include misalignment, where a building that was vertical begins to bend, and cracks that were not there before,” she says.

While repainting may improve appearance, it does not address the underlying structural and safety risks.

“When water penetrates, it weakens the integrity of materials over time, and in some cases leads to cracks or deterioration that may not be immediately visible,” she adds.

She cautions that before any cosmetic repairs are done, buildings must be thoroughly dried and assessed, especially because flooding can also affect electrical systems.

On construction materials, Prof Wanjiku notes that most standard materials can withstand moisture if used correctly.

“Masonry, concrete and steel can survive exposure to water because they are designed to resist humidity. However, materials like cardboard will not. Even with water-resistant materials, if the design is poor and elements are not properly tied together, the building will still be damaged,” she says.

Zoning also plays a critical role in determining how vulnerable buildings are to flooding.

“When zoning is not properly enforced, people build in areas prone to flooding, such as riparian zones, wetlands and low-lying areas.

These spaces are meant to absorb excess water, but construction interferes with natural flow and increases flood risk,” she says.
In extreme cases, oversaturated soil loses its ability to support structures, leading to partial or total collapse.

Poor planning

Stephen Lutta, an architect and sustainability consultant at Bomani Consulting Group, says the flooding crisis reflects poor planning and uncoordinated development.

“The biggest gap is the lack of a coordinated master plan that aligns development with infrastructure such as drainage, sewer systems and waste management. The city is growing faster than the plans in place,” he says.

He notes that some developments sit on drainage paths or block natural water flow. “When infrastructure is not planned, people end up building on drainage channels. When heavy rains come, the system cannot cope.”

Waste management further worsens the situation.

“Garbage blocks drainage systems, and when floods occur, that waste spreads across neighbourhoods and into rivers. The existing infrastructure was not designed for the current population, so it becomes overwhelmed,” he says.

Lutta also raises concerns about construction quality.

“Many buildings are put up by unregistered professionals who take shortcuts. They focus on the structure without considering the surrounding environment. In low-lying areas, buildings should be elevated and supported by proper drainage. Without that, they become vulnerable.”

He emphasises that even well-designed buildings depend on proper infrastructure.

“Climate resilience starts with infrastructure. You can have a well-designed building, but if drainage, sewer and road systems are inadequate, it will still be affected.”

He points to cities such as Kuala Lumpur as examples of effective flood management.

“They receive more rainfall than Nairobi but have managed flooding through proper planning, large drainage channels and strict waste control. These are lessons we can adopt,” he says.

“We are building first and adding infrastructure later. That approach will keep exposing us to the same problems every rainy season.”

The damage caused by flooding is also influencing real estate decisions, with property values increasingly tied to flood risk.

Floods and valuation

Eric Nyadimo, President of the Institution of Surveyors of Kenya, says location is becoming more critical in valuation.

“If an area is prone to flooding, investors shy away because floods damage property, which directly affects value,” he says.

Over time, areas frequently affected by floods lose their appeal.

“Investors avoid them, and land use becomes limited because only certain developments can be done safely.”

Soil composition is another key factor in how buildings respond to heavy rains.

“You need well-draining soil. Clay soil retains water and becomes waterlogged, meaning developers must dig deeper to reach stable ground. If this is not addressed, the building is at risk,” he says.

Unstable soils

He also points to loose soils such as volcanic ash found in parts of Kajiado and Naivasha, which are unstable and affect how structures sit.

Beyond soil, drainage remains one of the most overlooked aspects of development.

“When putting up a development, water must be directed into proper channels. Flooding happens when drainage points are too few, too small or blocked,” he says.

Flooding, he adds, is not always about the volume of rain, but how water is managed.

“You may find an area flooded, then a few hours later, the water clears. That shows the problem is often the inability of drainage systems to handle large volumes at once.”

He adds that development on previously swampy land is possible, but only with proper planning.

“Nairobi itself was once a swamp, and measures such as planting eucalyptus trees helped absorb excess water. The problem comes when development happens without proper engineering and planning.”

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