Excavations and Basement Tanking for Buildings in Kenya.
Construction projects in Kenya have now advanced to a point where its feasible to make use of underground basements plus several high rise stories so as to increase the built up plinth area. As land becomes a scarce resource , Kenyan buildings are increasingly faced with the need to excavate and increase building plinth area downwards as well as upwards.
In most cases, excavated spaces are converted into basement car parks, which can go to several storey levels downwards. The NSSF Building near Jeevanjee that houses Nakumatt supermarket has the deepest basement in Kenya, several floors below ground floor level.
Excavation is done using excavators which load the soil into dump trucks for onward dumping into approved dumping sites around Nairobi.
Basement tanking refers to methods of water proofing the basement walls and floors from underground water. Nairobi and its surroundings sits on an area with very low water table so basement tanking is critical.
Water can damage the walls and floors, making the interiors unhealthy for human habitation due to mold and fungi. If in excess, it can also damage the structural integrity of the building.
The building that colapsed in Mlolongo a few years ago was on swamply ground.
The building that collapsed off Jogoo road last year was also on swamply ground.
Jogoo House, in Nairobi CBD, also has basement walls and floors that are in an area that is full of swampy water.
Waterproof membrane layers are fixed in between the walls to prevent the water from leaking into the building interior.
A water pump is then installed to pump out the seeped water.
Waterproof coating is stuck onto the wall and floor surface. Some coatings are full vapour such as epoxy and polyurethne, while some allow for breathing, which are mainly cement based. Tanking is good for areas without serious underground water amount and pressure. Most of Langata, CBD, jogoo road, Runda areas require more of lining rather than tanking since they have high underground water volumes.
Architect Francis Gichuhi Kamau.