Explaining their 2003 decision to renovate, the society's general manager of project management, Chum Hon-sun, says: 'If we tore it down, we would also have to look into where to move the residents.

'Economically, we'd have to put in more resources in order to redevelop. Socially, we wanted residents to be able maintain their strong community ties and daily routine as the majority have been living here for many years.'

Then there were the environmental considerations. Renovation was expected not only to add at least 20 years to the life of Moon Lok Dai Ha, it also generated just 4,000 tonnes of construction waste compared to 10 times that amount if the estate were to have been demolished and rebuilt.

Amid worldwide concern over climate change, the need to improve energy efficiency and to reduce carbon footprints, architect Chris Law Kin-chung says it's wrong to make redevelopment a routine choice.

'While sometimes you need to demolish and rebuild in the public interest - if, for example, an MTR station or a hospital is needed - assuming demolition-and-rebuild as the norm is plainly wrong,' says Law, director of architectural firm the Oval Partnership.

The construction of any building requires the consumption of considerable energy and resources - from extracting stone and iron ore and turning them into concrete and steel, to transporting the material and eventual construction - and so therefore reducing sound structures to rubble is extremely wasteful.

Besides, 'demolishing a building is an extremely polluting process', Law says. 'There's the air and noise pollution, and much of the material in concrete structures cannot be recycled and simply goes into landfills.'

Even if scrap steel is recycled, it has to be transported elsewhere and melted down.

Rather than spend HK$530 million redeveloping the site, the Housing Society opted for a HK$130 million upgrade that has turned Moon Lok Dai Ha into an attractive residential complex with elderly friendly features such as ramps and non-slip tiles, energy-efficient fittings and lifts that stop at every level instead of every four floors.

There's also an air-conditioned lounge with television, internet access and mahjong tables. In the courtyard, shades were installed over benches where residents often gather. Some ground floor units were turned into elderly friendly flats, with supports in the toilets and easy-to-reach switches.

A gardening patch offers another opportunity to socialise as well as grow vegetables such as onions, tomatoes and cabbage.

Choi Lin-ho, a grandmother who has lived on the estate for 44 years, appreciates not having to climb several flights of stairs. 'We really wanted to see the estate revamped, but the change that I like the best is the lift,' she says.

For serviced apartment operators such as Shama, renovation makes better sense than rebuilding. 'We found the fastest way to work in this city is to buy buildings that are well-located and add value,' says Shama CEO Elaine Young.

Only large developers have the capital to buy a site and spend four or five years erecting a new block, she adds.

Among Shama's newest properties is a 46-year-old commercial building in Fortress Hill, which has been transformed after an overhaul into a sophisticated apartment block. By carrying out major repairs, Shama avoided having to create rubble by razing the block, and then using another 1,500 tonnes of concrete and 50,000 square metres of wood to erect a new tower in its place.

Getting the shabby 18-storey structure up to scratch, however, tested architects' ingenuity. The concrete was crumbling in places and floors were uneven. Extensive illegal construction made existing structural plans obsolete, so fresh ones had to be drawn up. An extension block tacked on to the back of the building had to be properly integrated into the structure, a third lift installed to cater to the handicapped and all the plumbing and wiring redone.

But the result is a triumph. By introducing picture windows and redrawing the layout more efficiently - including reinstating balconies that were illegally enclosed - the designers have created airy, light-filled living spaces. Use of double-glazed glass and energy-efficient lighting has also helped cut electricity bills.

'Tenants are now starting to get environmentally conscious, so it's now almost expected that we try our best,' says Young.

The prospect of a faster turnaround also prompted owners of The Phoenix, a 22-year-old building in Wan Chai, to overhaul it instead of rebuilding.

'Renovation is actually a low-risk strategy for a developer or a fund,' says Stephen Jones, regional managing principal at Woods Bagot, the international design firm behind the renovation. 'This project took 18 months compared to three or four years for a new building.'

Woods Bagot often recommends that clients renovate whenever possible not only because it's environmentally friendly but also because it makes economic sense.

'It's pretty hard to turn a 1960s office building in Tsim Sha Tsui into a Grade A office building, but you can reposition it in the market,' Jones says. 'It is possible to change their function; it's easier to turn an office building into a hotel or serviced apartments, for example.'

At The Phoenix, Jones and colleague Mathilde Lucas exposed ceilings to add height and opened the facade to let in light and create loft-style, boutique office space. The idea was to attract tenants in creative fields such as design, architecture and marketing rather than the trading firms that used to occupy the building. 'This reflects how Hong Kong is moving from a production base into a intellectual property base,' Jones says.

With 89 per cent of power consumption in Hong Kong linked to buildings - for air conditioning, lights and operating lifts - improving insulation and energy efficiency is a key element in retrofitting for a greener world.

'Better insulation - using thicker walls and double-glazed glass, for example - can cut electricity bills by 40 per cent to 50 per cent,' Law says.

The introduction of energy-saving lights in his office has reduced power bills by 30 per cent.

Jones and his colleagues didn't have to contend with overheated west-facing walls at The Phoenix. Nevertheless, they installed efficient air conditioning and compact fluorescent lighting, which save energy and produce less heat. 'Control systems to switch off electrical appliances after hours are as important,' he says.

'More people under 40 are demanding that their workplace be responsive to world issues and sustainability is one of these issues,' says Jones. 'It's about a 2 to 3 per cent additional cost compared to how much companies might be willing to spend to increase productivity significantly.'

Law says the market is skewed in favour of new construction and that the government should encourage renovation by providing loans for retrofitting and introducing more flexible zoning codes to attract new investors. 'The cost of renovating a square foot of land is less than rebuilding,' he says.

Balance sheet aside, Law says renovation makes more sense from an urban planning as well as macro-economic view. 'An established community is a closely linked economic network honed to high efficiency over the years and there's a loss of economic efficiency if people are regrouped,' he says, citing old parts of Wan Chai.

Moon Lok stood out over its care for elderly residents, who didn't have to move while work was ongoing. 'We took care to bring in our architects after hours to explain what they might expect during construction,' Chum says.

To minimise disruption, contractors set up lounges and quiet corners which residents could escape to while renovation was going on near their homes, and consulted schools to work around exam schedules.

'We're really proud of the new building and you see quite a lot of people in the lounge,' says Woo Yee, a mutual aid committee chairman.

With successful retrofits such as The Phoenix, Law questions whether Hong Kong needs many new commercial buildings when vacated industrial buildings could be adapted for new use. 'Unlike 40 years ago when there was a need for new construction, today 95 per cent of our building stock is existing. Shouldn't we focus on attracting investment into making sure these structures are safe, efficient and environmentally friendly?'