Mandatory soil test looms for developers before construction

Soil testing is now mandatory before construction, as stipulated in the National Building Code 2024, which took effect in March. The code provides more strict standards to the industry, including the provision of sanitary facilities and a changing room at the construction site.

The facilities, which should be done at a ratio of one for every 30 workers, must also be kept clean at all times.

The long-awaited code replaces the 1968 laws that players in the construction space had long lamented for being outdated and not cognisant of the emerging building technologies in the wake of climate change.

The National Construction Authority (NCA) is currently doing sensitisation of the code among industry players.

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In case a structure is being set up on a slope or unstable soil, the approving authority will inform the contractor or developer.

“Where the owner is informed under sub-paragraph (1), and if any unstable soil or unstable slope is evident within the construction site, the owner shall submit to the approving authority a statement prepared by an engineer specifying the measures necessary to provide for any differential movements or other effects on the construction site referred to in sub-paragraph (1), which may be detrimental to the building,” the code reads in part.

It states that the soil in a construction site, defined as in KS ISO 11074 (soil quality vocabulary), shall be treated in accordance with the recommendations of KS 999.

KS999 are the specified methods of tests for civil engineering purposes as provided by the Kenya Bureau of Standards (Kebs).

It further insists that a soil test is procedural for a structure that is meant to house more than four floors.

“A design of a foundation for a building of more than four storeys shall be preceded by a geotechnical report determining the critical design parameters, including—(a) allowable bearing pressure; (b) cohesion of the soil; and (c) content of chlorides and sulphates in the soil,” the code says.

It adds that soil structure should also be considered when putting up the foundation of a load-bearing structure of a single-story building, constructed as a strip foundation (shallow foundation) of plain concrete situated centrally under the walls or piers. This shall be constructed in such a manner that no weaker soil exists below the foundation.

The foundation should also be able to withstand pressure according to the type and condition of the soil as specified.

“If a single-storey residential building is constructed with external walls of a thickness of 150mm, the thickness of the concrete used in the strip foundation may be reduced to at least 150mm if the bearing capacity of the subsoil is at least 75kN/m2,” the code says.

In cases of black cotton soil, which is known for expanding and shrinking, the code has stricter specifications.

“Where a floor is to be constructed on a construction site consisting of black cotton soil, the black cotton soil shall be entirely removed down to rock level or removed to such other level as may be approved by an engineer,” says NCA in the code.

It adds that for floors constructed on black cotton soil subject to excavation, the area shall be filled with suitable hardcore consolidated and blinded with fine material to a level finish.

“Where, the depth of the black cotton soil referred to in subparagraph (1) does not exceed 1.8m— (a) the soil shall be removed to a depth of at least 0.9m; (b) a construction site overlay of 100mm thick of consolidated murram, or 75mm thick of concrete of a strength of at least 1:4:8 shall be laid; and (c) the remaining excavation shall be filled in the manner described in sub-paragraph (2),” the code states.The code also requires the owner of the development to put up not only a contractor’s shed but also sanitary facilities for the personnel. Failure to do this can lead to suspension of the work by NCA.

“An owner shall not engage in construction works without providing sanitary facilities for all personnel employed on or in connection with the construction works,” the code says in paragraph 57 (2).

It adds that these facilities should be clean and hygienic at all times.“When the sanitary facilities have not been provided in accordance with sub-paragraph (2), the approving authority shall direct the suspension of construction works until the required facilities are made available,” the code reads.

If the approving authority considers that the construction works are not per the code, it may order investigations and order the owner of the building to provide proof that the dealings are in order.

It can also issue a test to be carried out or, as specified in paragraph 53(1)(c), cause the construction works to be cut into, laid open, or demolished to the extent required by the approving authority. An owner who has been ordered to cause construction works to be cut into, laid open, demolished, or tested shall not continue with any works affected unless authorised by the approving authority.

“Where a cutting into laying open, demolishing, or testing reveals contravention of this code or any approval granted, or if the necessity for cutting into laying open, demolishing, or testing is attributable wholly or partly to a contravention of this code, the cost of the works shall be borne by the owner,” the code states.