Experts explain why Gen Katumba banned use of timber in constructing slabs

Kampala, Uganda | THE INDEPENDENT | The National Building Review Board-NBRB has said that using steel-timber-concrete method to construct slabs is unsafe since there are no clear standards for the timber being used.

The clarification follows the 19th September 2022 ban by the Minister for Works and Transport Gen. Katumba Wamala on the use of Steel-Timber-Concrete (STC) composite building method.

According to the Executive Secretary of the NBRB Flavia Bwire, the STC composite building method is a patented method by a Ugandan she declined to name. She says that the board received information about a new method being used in the construction of storeyed building which was different from the conventional methods.

In this method, constructors use a combination of timber and concrete to lay the slab which is different from the conventional methods where the slab is composed of concrete and steel locally known as ngalama.

In 2020, Bwire says they embarked on a study to assess the safety of this building method by examining the viability of its various structural elements, evaluate the method against the conventional method, and assess the adequacy of the technical skills available for its implementation.

Bwire says that in the study, they asked the proponent of the method to give them a detail of any engineering studies conducted locally about the method, show them projects executed using the method, and the procedures followed to ensure safety which was subjected to an assessment.

She says that they visited five structures under construction by the proponent of the method and more than 20 others to establish how this method was being used and the integrity of the structures. Majority of the structures were in Kampala and Metropolitan Area except for two, one in Ntungamo and another in Mbale and Bwire says they were found to be compromised with the slabs not strong enough to support the weight of the next level of the structure.

Bwire says that they are working with local authorities, specifically building committees, to identify the structures being constructed with this method such that an assessment is done to establish their integrity and a remedy provided. Bwire says that for the structures they inspected, none of the drawings were endorsed by professionals and neither was building permission obtained from the local authority.

For structures that can be re-enforced, then developers shall be instructed to do so while those that are irredeemable shall be demolished.

The STC method is not entirely new as it has been implemented elsewhere in the world. But Bwire says that the country doesn’t know yet how to localize the method to suit the local resources. First, she says the study found that there is inadequate skilled workforce to design, erect and supervise structures constructed using this method. She says there are no certified welders yet the method involves the use of steel at critical steps of construction.

Bwire adds that the timber, the main material being used in this method is currently not graded and its quality parameters are not known and yet there are also no design standards or guidelines to support the technology both during design and implementation.

She says that they shall work with the academia to study this method and find how safe it can be implemented locally. The board shall also set up a technical committee to develop guidelines for the safe design, fabrication and erection of structures using this building method.

This method has been said to be cost-effective, with some developers saying it reduces the cost by over 35 percent. Engineer Moses Tiberonda from Muna Constructions Limited says that the method is fine but has room for improvement.

He says there is a weakness in the method at the point where the slab connects to the pillars. He says, the constructors use steel but it is not done professionally which makes the joint weak.

Tiberonda says that there are structures made of steel but they are constructed using the conventional methods where the foundation is constructed using I-beams made of metal and concrete.

Section 42 of the Building Control Act, 2023 gives the minister powers after consultation with the board to prohibit the use of a building method or material in building operations when declared unsafe.

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