By Jude Njoku & Kingsley Adegboye
Mr Denis Ndegbu had the choice of buying a plot of dry land in Agbara, a Lagos suburb but rather opted to buy a water-logged land near Ijanikin, a nearby neighbourhood. Two factors influenced his decision – the cost of the two plots and their proximity to the road. The water-logged parcel of land was by far cheaper than the dry land and closer to the road.
Without doing any soil tests or engaging the services of any built environment professional, Mr. Ndegbu started to work on the site. He later discovered that he made a wrong decision after-all as the cost of sand-filling the land alone could have taken him far, if he had bought the dry land. When Mr Ndegbu ran out of funds, he decided to abandon the project.
The plight of Mr. Ndegbu is synonymous to what many Lagosians go through on regular basis because most parts of the city are water-logged and marshy. Some of those who succeeded, erected shanties that are at best, good for the habitation of wild animals.
Swamps are forested wetlands. Like marshes, they are often found near rivers or lakes and have mineral soil that drains very slowly. But unlike marshes, they have trees and bushes. They may have water in them for the whole year or for only part of the year.
Experts posit that the construction of houses on swamps require special attention. Either the soil is removed or strengthened by suitable means after ascertaining its (soil) properties. Building houses in challenging terrain and swamps requires special attention when compared to construction in ordinary soil. This is because swampy or marshy lands are periodically and at times permanently inundated by water.
Against this backdrop, the CEO of Ethical Business and Management Associates EBAM, Mr Afolabi Adedeji, a Civil Engineer, advised those who have bought swampy land to ensure that the foundation of their buildings rests on sound soil so that when the super structure (building) is completed, the weight would be evenly spread.
One of the first steps to take, according to Engr Adedeji is to sand-fill the swampy land so that it would become firm. When this is done, you should put a raft foundation to carry the building. The EBAM chairman was quick to point out that it is not in all cases that raft foundation will be effective.
“Sometimes, the swamp or what we call potopoto will be too deep that using the raft foundation will not solve the problem. In that case, you should go for a pile foundation,” he said, adding that there are two types of pile foundation – end-bearing pile foundation and friction pile foundation.
Adedeji who stated that it is preferable to look for virgin land that is firm because it costs less, however noted that in a place like Lagos where it is becoming increasingly difficult to get dry land to build, you cannot run away from building on swamps.
“What we should do is to apply engineering methods and techniques to get nature to suit our purpose,” he said, adding that most of Lekki and Ajah were swamps that have been turned into highbrow residential neighbourhood.
Also speaking on how to effectively utilise a swampy land, past chairman, Nigerian Institute of Building NIOB Lagos State Branch and National Publicity Secretary of the Institute, Mr. Kunle Awobodu explained that building on swampy land requires soil investigation.
He noted that where the water table is high, one needs to determine its capacity. Once these have been determined, the builder would now be left with the choice of the type of foundation that will be suitable on the land. The choice, he said, is between the raft foundation and piling.
Awobodu advised builders on swampy soil to equally take the future level of the road around the premises into consideration. He pointed out that if the level of the road is higher than the level of the foundation, the house will have drainage challenges.
Explaining that water from the ground will also pose a challenge to the building, he said this is why from the onset, the developer should use water resisting membrane to check dampness of the walls. According to him, the type of filling done before doing the foundation matters a great deal.
He advised developers on such land to avoid clay materials or soil when filling water logged areas. This is because when the water table diminishes, the clay will shrink thereby creating a space underneath the slab and causing cracks on the building in future. He further noted that in constructing the fence round the building, concrete must be used on the lower part of the fence above the proper floor level.
Finally, Awobodu said painting of the external walls of the structure shouldt be done with premium quality paint to prevent moisture on the building.