The method limits the use of concrete and steel, by replacing some of the load-bearing elements with timber. PHOTO/COURTESY

By  Taaka Wandera Kupewa

A number of construction projects have come to a standstill since the ban on the steel timber concrete composite building method (STC) by the Ministry of Works and Transport last month. 

Hebert Zziwa, the National Building Review Board (NBRB) spokesperson, says NBRB recommended the banning of the STC construction method based on a study carried out in 2020 on its viability.

The study revealed that there is inadequate skilled work force to handle structural steel structures in terms of design, erection and construction supervision. It also revealed that the timber, being used currently is not graded and that its quality parametres are unknown. 

Yet, the method limits the use of concrete and steel, by replacing some of the load-bearing elements with timber. Timber, even at its best has inherent shortcomings, how feasible will it be for one with questionable quality to efficiently develop robust and environmentally friendly structures? 

It was also noted that there are no design standards and guidelines to support the technology both during design and implementation. 

The study discovered that safety aspects such as the fire risk and earth quake resistance, have not been considered in design and implementation of this technology and that for the sites that were inspected, none of the drawings were endorsed by professionals and neither were building permissions obtained from the local authority. 

The findings from the study, show that the STC building method is not the problem, but that there are no standards and regulations on how it should be implemented in Uganda.   STC was registered as a Utility Model in 2019, and for it to have been registered, it must have undergone vigorous, strict testing before approval and certification by the relevant organs. While the construction industry stakeholders appreciate the body’s effort to promote safety, they are unhappy by the way it has been handled.

What next for contractors? Dalton Semaganda, a contractor from Nana Consultancies says they were not given the due consultation they deserve as industry players.  

“The challenge we have is that the industry has so many unskilled people who look at what we do and think they can just replicate. While some of us are doing the right thing, it is no secret that there are others doing shoddy work that has resulted in loss of property and lives.  The course of action have been to put in place a strategy that would weed out the malcontents but allow those who are doing the right thing to go on with their work. The ban has left us in limbo, and it is affecting our businesses since we have employees to pay and clients to serve,” says Semaganda.

Justus Ocheng, an architect is of the view that banning the innovative construction method might just be a case of a bad work man blaming his tools.   

“If there are no standards and regulations is that not what should be addressed? STC is not a new method, it has been successfully used in other countries, where they have proper standards and regulations.  It is therefore, surprising that the method has been suspended, notwithstanding its potential to lower the cost of housing construction. We all agree that safety is fundamental but by the time this method was approved, it certainly met a minimum standard of safety. 

Government needs to focus on regulating the way STC is applied and not to simply prohibiting it. This ban can be a stop gap to enable setting up of regulations, improving skills and other necessary procedures,” says Ocheng.     

The architect stresses that what is key therefore, when it comes to the safety of any building method, is quality control.  “Just as any other processes of construction, there are gaps in implementation, gaps in quality control and gaps in skilling. We would like to see to what extent these gaps can be addressed so that whatever cost benefits are there can be gained but not at the expense of safety,” he adds. 

Skilling of professionals, to better inspect and monitor proper implementation of projects is also very essential. Proper guidelines without people to enforce them is pointless.  However, Zziwa, stresses that it would be counterproductive to ignore the method’s inherent structural weakness for any reason.  

“Of what use would it be to construct a building cheaply only for it to collapse shortly after completion putting people at risk?  For now people should revert to the traditional method,” Zziwa urges. 

Is STC really cheaper? While majority stakeholders say it is a cheaper building method, others think otherwise.   “STC is quite costly, and the only reason people claim it is cheaper, is because they are not using the right standard materials, but when you use the right standard of construction materials, especially for smaller projects, it is a more expensive method, I know this because we are partly using STC for an ongoing project,” says an architect who preferred anonymity.   

“Take the steel, for example the steel suitable for STC is structural steel, which is quite expensive, there is no company manufacturing structural steel in Uganda, so we have to import it. The timber suitable for this method must be treated, laminated and compressed to take out all the air bubbles and cured to make it almost as hard as metal; another costly process. Therefore, majority of people are using very bad untreated timber. I always get surprised to see that some of these buildings are actually still standing. The presumed benefits must be taken with caution,” she explains further.    

Moving forward Having access to quality affordable housing is fundamental to reducing poverty, improve equal opportunities and guarantee a sustainable growth, which is why it became the objective of UN Sustainable Development Goals (SDG) number 11. 

Across the continent, there have been several innovations in the construction industry, which are fostering the development of this basic human need. The steel timber concrete composite building method (STC), construction technique has received increased interest recently both negative and positive.  Buildings consist of many types of loadbearing elements, such as foundations, walls, columns, braces, girders, beams and floor systems. Each of them has a specific purpose and unique demands controlling their design and construction. This is why NBRB has deemed the use of steel-timber concrete composite building method unsafe.

Flavia Bwire, the NBRB executive secretary says they are currently setting up a technical committee comprising of civil engineers, architects, regulatory and professional bodies to study the building method and develop guidelines for safe design, fabrication and erection of structures.        Why is it popular? Dr Nathan Kibwami, a quantity surveyor and the president of the Institution for Surveyors says the STC is popular because it has a number of perceived economic advantages.  “STC is considered a cheaper method of construction, because it does not consume as much cement as the conventional reinforced concrete method. For example it is claimed that a project which would say, need 300 bags of cement while using the reinforcement concrete method, when using the STC method the construction will need 200 less bags. Another economic advantage with STC, is that it does not require the use of steel re-enforcement bars (mitayimbawa) plus other jointing materials such as maxi pan, rings, among other materials as is with the conventional method, so a lot is saved from here,” Kibwami says.   Another great advantage, is that it is quicker to install (increased speed of construction) and dismantle.  “When it comes to the slab for example, while using the traditional method, the iron bars are set up first, then the concrete is poured through and has to dry first before construction can continue. On the other hand, STC has a shorter process because it uses the composite of the three materials.  It is also considered more environmentally friendly, because it substantially reduces the overall carbon foot print of buildings and has low maintenance costs throughout the lifetime of the buildings,” he adds.    Currently, buildings consist of reinforced concrete or steel-concrete composites, cast in situ. Concrete is poured into formwork and propping is then required for at least a week. This is a wait of at least 10 days between storeys.  Building with steel-timber composites means there is no waiting and upward construction can be seamlessly ongoing.  Because the material is lightweight, it reduces cranage and consequently injury risk. Therefore, steel-timber composite floors can significantly increase speed of construction and reduce the noise and pollution associated with construction activities.

Why is it popular? According to a research paper published on frontiersin.org, timber-concrete hybrid building refers to the structure form dominated by wood structure and concrete structure. The most common type of tall wood hybrid structures is combining a case-in-place concrete core that resists the lateral loads, with the timber structure carrying the reminder of the gravity load and diaphragm loads.  According to relevant research, timber concrete hybrid structure gives full play to the best performance of wood and concrete, and has higher bearing capacity, fire resistance and seismic performance compared with pure wood structure (Poirier et al., 2016).

Moving forward Flavia Bwire, the National Building Review Board (NBRB) executive secretary says they are currently setting up a technical committee comprising of civil engineers, architects, regulatory and professional bodies to study the building method and develop guidelines for safe design, fabrication and erection of structures.    

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