Last week, business in Fort Portal Town came to a standstill after Corner Stone Hotel building collapsed. According to reports, the building collapsed under the weight of two water tanks which had been installed on top of a section of the building.
Fort Portal Municipal engineer Jimmy Balewa said due to the weight of the water tanks, the walls developed cracks forcing the building to collapse. The tanks had a capacity of 20,000 litres of water each.
According to Beatrice Nalubega, a mechanical and electrical engineer, the location and placement of the rooftop tank is determined by the location of the washrooms.
Plan for it
“The tank should be considered from the beginning of the structural design. You are required to hire a licensed architect or licensed structural engineer to conduct a thorough critical structural examination of both the water tank and the water tank support structure for approval,” Nalubega notes.
The engineer says that usually a separate slab has to be added on the part of the roof on which the tank sits. “The roof must be reinforced to add strength and to elevate the tank which helps with the water pressure otherwise at lower levels you many need to boost the water to the above floors,” she explains.
To protect the structural integrity, the engineers should determine the tank loads. “The water tank has a direct structural effect on the building. Since water tanks are filled up sometimes and at times empty, it becomes an interesting structural pattern making it a dead load at times and a live load during times of fluctuations (in case of irregular water supply).
These two load patterns (dead and live) have different factors of safety meaning the problem provides a unique engineering challenge that should be handled by qualified personnel,” Pius Louis Chelimo, an engineer notes.
The loads according to Chelimo are dependent on the size of the water tank which is consequently determined by the water supply and demand pattern. “The demand is determined by the water use for an average household per month. The demand should match the supply. Water density is 1,000kg per cubic meter which means that for every 1000kg you will have 1,000 litres,” Chelimo adds.
Ronald Atwiine, a structural engineer, observes that rooftop water tanks are a major problem nowadays considering the rate at which they are reported to be the source of weakened or collapsed structures. He notes, however, that proper care should keep most problems at bay.
“When it comes to water tanks, preventive maintenance is the way to go. The water tank requires regular attention to prevent the need for emergency interventions which can be enormously expensive. To ascertain the safety of the structure, a critical structural exam should be carried out every year. If the exam reveals any structural or safety deficiencies with the water tank or support structure the owner must take immediate measure to secure and repair,” Atwiine advises.
The biggest problem of rooftop tanks is leakage. Water leaking from these water tanks overtime affects the strength of the walls and concrete, because of the continued dampening water eventually reaches the reinforcement causing rust, affecting its thermal expansion paint to swell and eventually peel off. Water damage is also a potential fire hazard.
“If your electrical wiring is present in an attic or ceiling, a leaky roof could pose a fire threat from shorted wires. It is highly recommended to have the wiring examined too when conducting the structural exam,” Chelimo advises.
The sanitary conditions of rooftop tanks are another worrying concern although not necessarily structural. There is a necessity for regular cleaning of the tanks because the water over time gets contaminated especially in cases where the cover gets loose. Flavia Namusoke relates how such an experience left her family members horrified.
“A few years ago, the cover of our tank fell off but we did not get to know about it until we started seeing maggots in our water. Apparently the water tank had been claimed by birds where they would bathe and leave droppings. We had to get someone to climb up to clean and put a more secure cover,” Namusoke narrates. Tanks should be cleaned at least once every year and checked in case of compromised water quality which is usually a sign of contamination.
Chelimo observes that like all engineering innovations there is a tradeoff between having a rooftop tank which is getting an independent tank stand.
He adds that this usually has the disadvantage of messing up the appearance of the structure, takes up extra space and comes with its own set of structural challenges.
“Most tank stands are constructed adjacent to the compound which in most cases reduces space that would have been used as parking or children’s play space,” adds Chelimo.
Building codes: If the house or business is located within an estate, the colour of your plastic water tank can be very important. Contact the estate management to ensure that the wrong colour tank is not purchased.
Water temperature: Dark coloured tanks, with black being at the extreme side of the spectrum, will always heat up more rapidly and to higher temperatures than lighter coloured tanks, with white being at the other side of the colour spectrum. This could be advantageous or disadvantageous, depending on the circumstances.
A point to bear in mind is that higher water temperature is conducive to algae growth. However, light transmission is another important factor in allowing algae to flourish – dark tanks let in much less light than white tanks.
A good compromise can probably be had by choosing a mid-spectrum colour such as green (if algae growth is an issue).