NAIROBI, March 19 (Xinhua) -- An increase in the number of buildings that have collapsed in Kenya in the last few weeks has exposed the gaps in the country's construction sector.

Kenya has a vibrant construction industry that has become a huge boost to the East African nation's real estate sector, with hundreds of houses being put up across the country each day.

However, as the sector booms, the increased collapse of houses especially during this rainy season points to the weaknesses in the industry, according to experts.

At least three storied buildings had tumbled in the last one week in the capital Nairobi due to on-going heavy rains in Kenya.

The latest incident involves a four-storey building in Ruai on the outskirts of Nairobi, which collapsed on Saturday killing at least two people.

The building that had initially been earmarked for demolition by the government as it was built on a road reserve that contained a restaurant and a lodging.

In the same week, a four-storey building in Kariobangi South and a five-storey building in Orion Estate-Juja crumbled.

Other buildings that have collapsed in the capital Nairobi this year include a four-storey flat in Zimmerman and a seven-storey building in Kware Pipeline Estate.

Experts blamed the tragedies to general lack of adherence to set rules by property developers as they rush to meet the high demand for houses.

"Most of these buildings are built in swampy areas, with the developers cutting corners ending up with weak foundations. Normally, the foundations on swamps can cost up to twice the construction cost on normal ground. Developers escape this by laying the substructure on hard-core instead of reinforced concrete strip footings," Nairobi-based investment firm Cytonn, which is also involved in real estate projects, said Monday.

The firm further noted that developers use sub-standard building materials, including scrap metal instead of steel to cut costs, while others ignore specifications for good mix of concrete, all which affect the strength of the building.

"Poor workmanship can also not be gainsaid as contractors employ unskilled workers to cut on construction costs," said the firm.

There is also poor regulation of the sector, with strengths of buildings not tested, as most small-scale developers ignore building and construction permits.

"There is need to plan our cities and towns so that buildings are not built on unsafe grounds such as swampy areas and near water banks," said Antony Kuyo, a real estate consultant with Avent Properties in Nairobi.

Kuyo further isolated ballast dust as one of the materials being used by developers to construct houses yet it is substandard.

Developers are using the dust in place of sand to cut costs, as there has been a sharp increase in cost of latter in Kenya's capital Nairobi.

Dealers are selling sand for up 50 dollars U.S. dollars per tonne from nearly half the amount as demand rises amid increased levies by government agencies and high demand.

Most of the sand used in construction in Nairobi comes from the neighbouring counties that include Machakos, Makueni and Kajiado.

On the other hand, a tonne of ballast dust, which is considered waste in quarries, is being sold at not more than 15 dollars. A property developer using about 100 tonnes of sand to build makes a huge saving if they use dust.

"This dust is used in constructing buildings of up to seven floors yet its joining properties cannot be compared to that of sand. The ballast dust cannot match sand when it comes to mixing well with cement to make stronger joints," said Kuyo.

Kuyo noted that to eliminate such gaps, the National Construction Authority must put in place strict regulations such as frequent inspections, training of artisans, easing the building approval process by reducing costs and time and ensure they are adhered to, and demolish the substandard developments.