A patchwork of deep red leaves and bright green grass stretches across the roof of a multi-storey carpark in Toa Payoh West. No one is allowed up there, yet the greenery can still be appreciated by many - those who live in the high-rise blocks around it.
From converted roofs of old carparks to landscaped decks in new housing estates, more such gardens in the sky are on the way.
About 28ha of greenery is now spread across more than 160 roofs of Housing Board blocks and carparks.
Over the next few years, another 43ha will be added - the area of almost 60 football fields.
"We are greening up a lot of HDB rooftops. It is pleasing to the eye, besides lowering the ambient temperature," National Development Minister Khaw Boon Wan noted in a blog post earlier this month.
Some, like the one in Toa Payoh West, are closed to the public. Located on top of older HDB blocks and multi-storey carparks, they cut the glare from the flat space, and add a splash of green.
"HDB continually works to identify the optimal locations for green roofs - for instance, carparks with many blocks that face them, so more residents can enjoy the view," said Mr Tan Sze Tiong, deputy director of environment and building performance research at the HDB Building Research Institute.
Carparks chosen are those with more than enough spaces.
But there is no problem if parking demand rises, for these green roofs are made up of portable trays that can easily be removed.
Their permanent counterparts are 100 or so landscaped public rooftop gardens which feature in the designs of new housing estates.
Many more are on the way. Since 2009, most new multi-storey carparks have been topped with these gardens.
They feature plants ranging from turf to trees, and often include a playground, fitness areas and games courts.
And the living rooms or bedrooms of surrounding units are carefully oriented to face these green havens.
"Rooftop gardens provide visual relief. Without them, you would just see an expanse of concrete," said HDB landscape architect Rachel Teo.
For Madam Sun Yuqin, the Punggol Regalia rooftop garden is not just a nice view from her balcony, but a place to exercise with friends every morning.
"It's quite a nice setting," said the 73-year-old.
Instant lush, green carpet
THE quiet, green roof in Toa Payoh West, set up in 2006, was the first of its kind. The lush carpet is actually made up of many small, interlocking plastic trays.
Known as the Prefabricated Extensive Green roof system, this low-maintenance arrangement was developed by the HDB itself.
For an instant green roof, these trays simply have to be laid in place - and left there.
Every six months, the plants are trimmed and fertiliser is added.
No watering is needed. A special compartment under the soil layer collects rainwater to tide the plants through dry spells of up to 21 days.
Tough, hardy species are also chosen. After much research, the HDB settled on two plants. One of them, Cyanotis cristata, even becomes more beautiful in dry weather.
Its leaves turn from green to dark red - "as though they are ushering in the autumn season", National Development Minister Khaw Boon Wan observed in a blog post earlier this month.
Another, Zephyranthes rosea, blooms with delicate pink flowers after rainfall.
Both species not only survived February's record drought, but turned lush and green again afterwards.