Better solar design was adopted in apartments to optimise comfort and reduce the amount of heating required in winter and air conditioning in summer, he said.

Healthier materials that did not emit toxic fumes into the air were used in construction, and properties were equipped with energy efficient lighting systems and appliances, he said.

Other green features included water efficient toilets, taps, showers and other fittings, recycling facilities, and green landscaping in gardens on roofs or on building facades.

'Developers can offer lower operational cost units, which become increasingly more attractive as energy and water costs rise,' Mr Carter said.

'Tenants always respond positively when they walk into beautifully daylit and thermally comfortable indoor environments. More sophisticated tenants recognise that environmentally designed apartments are much more comfortable and stimulating to live in than simple air-conditioned boxes.'

He also said that some people were concerned about the environmental challenges facing the world and were attracted to the idea of living in an apartment that helped reduce their personal environmental footprints.

Monica Lau Man-ching, residential leasing manager with CBRichard Ellis, said major landlords were providing comprehensive value-added services including green initiatives to increase the appeal of their luxury properties.

'You can find all kinds of green initiatives with the properties of big landlords, from separation of waste to recycling facilities, landscaped gardens and energy saving devices. Tenants are generally at ease about living in those residences as they are being well taken care of by the landlords,' she said.

But Ms Lau said that location, rental cost and unit size remained the key deciding factors for tenants to commit to a deal.

For tenants with children, the proximity to schools was a big consideration, while the provision of clubhouse facilities was also important.

Ms Lau said the leasing sector continued to be active and stable, while landlords were still aggressive in asking for high rents because of the strong leasing demand from tenants.

For luxury properties in popular locations, such as Island South, Mid-Levels, The Peak and Happy Valley, landlords were able to raise rents further, she said. Simon Lo Wing-fai, director of research and advisory at Colliers International, said luxury residential rental had increased by about 11 per cent so far this year. But there was still demand for luxury properties as individual occupiers preferred to lease rather than buy properties amid the uncertain market environment, he said. The shortage of new luxury supply in traditional residential locations supported the growth of rents with the sustained leasing demand, and several tenants had shifted to short-term leases with serviced apartments.

Home2home lifestyles management company, which operates serviced apartments under the Ovolo, Erba and Abeo brands, is among the boutique operators that have given a commitment to eco-awareness and sustainability. Its director of operations and project development, Heddy Li Suk-fan, said home2home's serviced apartments were created with environmentally friendly concepts in mind from the start, and the company worked closely with local architects KplusK, which promoted the use of eco-friendly design and sustainable building materials.

She said the application of LED lighting and compact fluorescent lights gave a new source of lighting, moving away from the traditional light bulb. The initial cost was high but in terms of longevity, they paid for themselves.

Commenting on overall market conditions, Ms Li said the company expected to stay at the forefront of the local serviced apartment market, and it had witnessed a steady leasing performance with an average of 95per cent occupancy.