Dengue danger zones: 5 design features prone to breeding mosquitoes

Ledges for air-conditioning condenser units collect water easily and many are inaccessible to residents for cleaning. Flat roofs, such as this one over a petrol station, can trap rain water and make it a prime breeding spot for mosquitoes. Ground spo
Ledges for air-conditioning condenser units collect water easily and many are inaccessible to residents for cleaning. Flat roofs, such as this one over a petrol station, can trap rain water and make it a prime breeding spot for mosquitoes. Ground spotlights used in condominiums and gardens in housing estates have rims that may collect water. The small openings of these drains make it very difficult for cleaners to carry out maintenance and get rid of puddles. Moisture and puddles can form in the space between the outer casing and inner container of many outdoor rubbish bins.ST PHOTO: YEO SAM JO ST PHOTO: STEFFI KOH ST PHOTO: YEO SAM JO ST PHOTO: STEFFI KOH ST PHOTO: STEFFI
Ledges for air-conditioning condenser units collect water easily and many are inaccessible to residents for cleaning. Flat roofs, such as this one over a petrol station, can trap rain water and make it a prime breeding spot for mosquitoes. Ground spo
Ledges for air-conditioning condenser units collect water easily and many are inaccessible to residents for cleaning. Flat roofs, such as this one over a petrol station, can trap rain water and make it a prime breeding spot for mosquitoes. Ground spotlights used in condominiums and gardens in housing estates have rims that may collect water. The small openings of these drains make it very difficult for cleaners to carry out maintenance and get rid of puddles. Moisture and puddles can form in the space between the outer casing and inner container of many outdoor rubbish bins.ST PHOTO: YEO SAM JO ST PHOTO: STEFFI KOH ST PHOTO: YEO SAM JO ST PHOTO: STEFFI KOH ST PHOTO: STEFFI
Ledges for air-conditioning condenser units collect water easily and many are inaccessible to residents for cleaning. Flat roofs, such as this one over a petrol station, can trap rain water and make it a prime breeding spot for mosquitoes. Ground spo
Ledges for air-conditioning condenser units collect water easily and many are inaccessible to residents for cleaning. Flat roofs, such as this one over a petrol station, can trap rain water and make it a prime breeding spot for mosquitoes. Ground spotlights used in condominiums and gardens in housing estates have rims that may collect water. The small openings of these drains make it very difficult for cleaners to carry out maintenance and get rid of puddles. Moisture and puddles can form in the space between the outer casing and inner container of many outdoor rubbish bins.ST PHOTO: YEO SAM JO ST PHOTO: STEFFI KOH ST PHOTO: YEO SAM JO ST PHOTO: STEFFI KOH ST PHOTO: STEFFI
Ledges for air-conditioning condenser units collect water easily and many are inaccessible to residents for cleaning. Flat roofs, such as this one over a petrol station, can trap rain water and make it a prime breeding spot for mosquitoes. Ground spo
Ledges for air-conditioning condenser units collect water easily and many are inaccessible to residents for cleaning. Flat roofs, such as this one over a petrol station, can trap rain water and make it a prime breeding spot for mosquitoes. Ground spotlights used in condominiums and gardens in housing estates have rims that may collect water. The small openings of these drains make it very difficult for cleaners to carry out maintenance and get rid of puddles. Moisture and puddles can form in the space between the outer casing and inner container of many outdoor rubbish bins.ST PHOTO: YEO SAM JO ST PHOTO: STEFFI KOH ST PHOTO: YEO SAM JO ST PHOTO: STEFFI KOH ST PHOTO: STEFFI
Ledges for air-conditioning condenser units collect water easily and many are inaccessible to residents for cleaning. Flat roofs, such as this one over a petrol station, can trap rain water and make it a prime breeding spot for mosquitoes. Ground spo
Ledges for air-conditioning condenser units collect water easily and many are inaccessible to residents for cleaning. Flat roofs, such as this one over a petrol station, can trap rain water and make it a prime breeding spot for mosquitoes. Ground spotlights used in condominiums and gardens in housing estates have rims that may collect water. The small openings of these drains make it very difficult for cleaners to carry out maintenance and get rid of puddles. Moisture and puddles can form in the space between the outer casing and inner container of many outdoor rubbish bins.ST PHOTO: YEO SAM JO ST PHOTO: STEFFI KOH ST PHOTO: YEO SAM JO ST PHOTO: STEFFI KOH ST PHOTO: STEFFI

This article was first published on July 28, 2014

Rubbish bins, flat roofs and spotlights may seem like regular, harmless fixtures in our working and living spaces, but they can silently harbour killers.

These are some areas that, because of their design, can turn into breeding grounds for Aedes aegypti, the mosquito which transmits dengue fever.

Earlier this month, dengue cases at Ferraria Park condominium in Loyang were traced to a design fault - heavy concrete paving slabs which allowed water to seep between them into hidden drains below, where mosquito larvae were found.

After visiting the condo, Second Minister for Environment and Water Resources Grace Fu said the authorities will detail and flag the construction sector design features that make maintenance hard and pose a danger as mosquito breeding places.

The Straits Times spoke to estate managers, pest control experts and town councils and came up with a list of five designs that are prone to breeding mosquitoes.

yeosamjo@sph.com.sg


FLAT ROOFS

SOME buildings, such as factories and petrol stations, come with roofs that are flat.

Pools can form on the surface if they do not have enough of a gradient for water to run off, said Mr Carl Baptista, director of pest control company Origin Exterminators, who has encountered breeding on such roofs.

"If there is enough of a slope, the potential for water to accumulate will be hugely reduced," he said.

Roof access is also a problem.

"Most roofs can only be accessed by cat ladders and trapdoors. But it's a chore to climb them, especially if you are a cleaner or pest controller who has to carry brooms or other equipment," said Mr Teo Poh Siang, managing director of property consultant Wisely 98.


SPOTLIGHTS WITH RIMS

CONDOMINIUMS often use ground spotlights to light up their name signs, and some of them come with rims that surround the bulb.

"The rims are there partly to prevent glare and for directing light at a specific spot. But it's like a cup that's facing upwards, so of course it will collect water," said Mr Chan Kok Hong, president of the Association of Strata Managers and managing director of real estate consultant company SavillsCKH. He added that such spotlights are also used extensively as garden lights within some estates.


DOUBLE-LAYERED BINS

MANY outdoor rubbish bins consist of an outer casing and an inner container.

But the space between these two layers can be a hazard because it collects water when it rains, said Mr Teo Poh Siang, managing director of property consultant Wisely 98.

While many of these bins now come with holes at the bottom of the outer layer for water to escape, their double-layered design may continue to trap moisture.

"Puddles can still form inside if there is rubbish or sand blocking the holes," said Mr Teo.


AIR-CONDITIONING LEDGES

APARTMENT buildings usually come with ledges for air-conditioning condenser units.

But these horizontal ledges are prone to collecting either rainwater or condensed water that drips from the units, said Mr Chan Kok Hong, president of the Association of Strata Managers.

"I have conducted building inspections and all these ledges collect water," he said, adding that many are inaccessible to residents.

"It's a perfect place for breeding mosquitoes."

He added: "We can't prevent every puddle from forming, but we can do something about these ledges.

"Maybe design them as perforated metal plates, or provide easy access."


UNDERGROUND DRAINS

MANY public carparks and driveways have underground drains with openings that are either too small or too far apart.

This makes maintenance tricky, said Tampines Town Council general manager Chan Wee Lee. While his team ensures that these drains are either oiled or flushed out with water, the openings pose an obstacle. He said: "The openings can be 5-6m apart, and so small that it's not possible to crawl into them.

"This makes some areas in the drain hard to reach, and mosquitoes may breed in small puddles there."