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Why the flat-roof craze is failing homeowners
A partially built prefabricated house with flat roof. Construction experts say hidden and flat roofs can perform well when properly designed and maintained, despite growing concerns among homeowners over persistent leaks.
Mary Kageni, a homeowner in Gikambura, Kikuyu, dreads rainy seasons. Each gathering cloud signals, but the likelihood of fresh damage to her flat-roofed house. A leaking roof has become the most punishing aspect of her homeownership.
She picked a hidden roof design because of its minimalist beauty, and the architect supported her choice, adding lower cost to the list of advantages attributable to the design.
But since she moved in, she has struggled with one leaking point after another, and she is wondering whether it has got to do with the design of the roof or poor workmanship.
“I have actually been thinking about changing the whole roof, especially when you go online and read all the concerns that other people raise about hidden roofs,” she says.
Construction experts say the blame is not on the roof design but on how it is executed, the workmanship, material and maintenance. The hidden-roof concept is still relatively new in Kenya’s residential market, meaning that a majority of foremen have little or no experience executing the design. For those who have never built one, or have supervised only a handful of such homes, the risk of costly mistakes is high.
John Inya, an architect at Rovel and Steel, notes that there is confusion between a hidden and a flat roof. He notes that a roof whose slant is below seven degrees is generally considered to be a flat roof, while above seven degrees is a pitched roof.
A roof can thus be pitched, but if it is concealed, then it is categorised as hidden. The one which Ms Kageni has is a butterfly shaped hidden roof. It has a common trough running at the centre with tilted iron sheets feeding it from the sides like wings, creating an image of a butterfly.
Mr Inya notes the hidden roof design was mainly used in the construction of shops in the villages. However, with the village shops, they used to have open backs so the water drained off to the ground, unlike the new residential ones, where the water converges in a gutter placed at the centre.
“The first issue is usually how the gutter is designed. Is it wide and deep enough because if it is narrow and you have iron sheets ending over the gutter, rainwater may fail to fall in the gutter and instead go directly to the opposite side and flow into the house,” says Mr Inya.
He notes one can use a concrete gutter or a metal sheet, but insists it has to be waterproofed to ensure there is no spillage, especially at the joints for the sheets. Some of the sealing material available includes bituminous felt, commonly referred to as APP.
Draining of gutter
George Owalo, the structural engineer, also points to the draining of the gutter as a major cause of leaks. He reckons that most builders do not have a large enough water outlet for the gutter, resulting in backflow, which spills into the house.
“Gutter is usually the issue because it is hard to quantify the rain. Sometimes you will get an El Niño - so how big is your gutter?” he says. “The outlet also has to be very effective and be well-maintained during the dry season because if the rains find it clogged, then there will be leakage,” he adds.
Those who put iron sheets for the gutter are asked to ensure they use heavy gauge mild steel plates and have a torch applied bituminous felt for waterproofing on top.
“I had an experience where I was called to sort out a problem. They had a deep gutter, but then it wasn't wide, so working on that space was a problem, and we were trying to introduce APP into it. So the gutter has to be wide and deep,” said Mr Inya.
The architect and the structural engineer agree that hidden roofs have the advantage of cost as they use less material, especially when the pitch is low.
The design doesn't need a fascia board finishing, and the corrugated sheets used don’t have to be expensive, for they have no aesthetic purposes.
A slab flat roof would be costlier than the hidden one due to the cost of laying concrete and the steel required for reinforcement.
“There is no need to use stone-coated iron sheets in a hidden roof because no one will be seeing it. If you're hiding it, then you simply use a simple corrugated aluminium sheet provided you're using a correct gauge and good quality supply,” said Mr Inya.
He advises homeowners struggling with leaking roofs to get a structural engineer to do checks before making any adjustments.
He notes relying on the foreman to diagnose a problem, which could be a matter of execution, would result in spending more without satisfactory results.
He noted that most developers do not engage structural engineers on the roofing designs and specifications.
“We usually adopt what we have seen in other regions, thinking it’s just for aesthetics, but there's a functional bit to it. Like in the western region, there are a lot of high-pitched roofs copied from Uganda, which copied from Europe,” said Mr Inya.
“People tend to think that the higher the slope of the roof, the more prestigious it is. What we forget is that the cost goes higher as the slope sharpens,” he adds.
He reckons the high pitched roofs are appropriate for areas that have snow, ensuring the weather elements roll over, ensuring they don't load the roof.
However, in tropical weather, we don’t need the high-pitched, which is expensive but friendly pitches that allow for water to flow.
