Are Flat Roof Homes Cheaper?

Once a preserve of the Coastal people due to Arabic influence, flat-roofed houses seem to be gaining traction in mainland Kenya.

The roof design characteristic of Egyptian, Persian and Arabian architectural styles seems to be a go-to for several homeowners mostly in urban areas as it has the allure of minimalism and modernity.

The symmetric geometries that come with a flat roof make the home stand out, especially in neighbourhoods where few or no individuals have similar designs.

James Onyando, a real estate consultant with Probuild Integrated Projects, says that just like fashion, architectural trends change with time and both developers and homeowners are widely adopting or preferring flat roofs to pitched roofs.

This, he points out, is driven by a growing feeling by developers that conventional sloped or pitched-roof architecture is old fashioned.

“The current generation of homeowners seem to be falling into this whole modern/contemporary language of the building,” says Mr Onyando.

Simon Ng'ang'a, a managing director of Symonns Realty, agrees with Mr Onyando but puts the new craze for flat roof design by homeowners in urban areas down to two factors; reduction of land sizes and cost of timber in Kenya.

He says that a majority of homes in the urban areas are built on an eighth of an acre which does not leave one with a lot of room for a garden and entertainment sections and as such most builders opt to maximise on space by opting for the flat-roof design which can be used for such activities.

“Further, the cost of timber has skyrocketed in recent times. The cost of roofing timber combined with preferred roofing materials, make this a very expensive venture for most builders,” says Mr Ng’ang’a.

He explains that a flat roof’s main attraction is the added space that a homeowner or builder can play with which is turned into a mini-garden, entertainment area, a terrace, a rooftop lounge area, patio, gazebo, or partly enclosed to create a penthouse; all which are quicker to install and also easier to maintain due to lack of slopes.

Ephantus King’ori, a co-director at Abib Jaus, a construction company that specialises in designing and building flat-roofed houses — points out that some homeowners even opt to mount a swimming pool on top of the roof, after adding additional waterproofing component, as the pitch of a flat roof is gentle enough to allow the surface to be used for such activities.

“It is relatively cheaper to install compared to pitched roofs especially with the increased cost of timber. Labour for construction is also cheaper since installation is relatively quick,” adds Mr Onyando.

Construction experts say that ethylene propylene diene monomer (EPDM) rubber, modified bitumen, thermoplastic polyolefin (TPO), and built-up roofing (BUR), is the widely used means of constructing flat roofs, with the BUR being the most common in the country.

A flat roof requires a normal slab either solid or hollow pot as designed by a structural engineer, integrated with waterproofing materials and finished to slope towards rainwater downpipes.

The finish on the slab is mixed with waterproof cement, which is then sloped towards the edges and corners where the rainwater downpipes are located.

There is also an additional waterproofing treatment done using products like APP or Dr FixIt which further ensure that water permeability within the slab is also highly reduced or eliminated.

“There are calculations done considering the area of the roof and the maximum volume of water expected during a heavy downpour in the particular region that the building will be located,” Mr Onyando says.

“These calculations determine how many downpipes would be suitable for the volume(s) of water calculated off the roof.”

But in as much as flat roofs can be done anywhere, the waterproofing agent may fail.

Mr Ng’ang’a points out that flat roofs are suitable for dry areas as there are more risks in areas that continually receive heavy rainfall, because with time, depending on the quality of the material used, the roof can get saturated, leading to leakages.

And this is where most disadvantages of the flat roof design come in with the Symonns Realty MD advising against flat roofs in areas that receive heavy rainfalls as any cost-savings at the point of installation will be lost with future repairs.

“Repairs costs can be more expensive than for pitched-roofs and in the long run, flat roofs also have leakages more so if they are poorly maintained,” he says.

This downside, however, says Mr King'ori, can be overcome by investing in high-quality building materials for waterproofing.

But if maintenance is poorly done, the structure of the house might be jeopardised and flat roofs end up being more expensive than pitched roofs.

“If waterproofing is not done properly by professionals it can lead to major leakages which may prove quite costly in the long run to maintain,” Mr Onyando says, adding that during hot weather, waterproofing membranes tend to radiate heat into the interiors of the house especially in cases where a solid slab has been used.