The letters touching on collective sales failed to touch on the principle underlying such sales - urban renewal.

In Hong Kong, clusters of dirty, rundown apartments are visible in parts of Kowloon, Causeway Bay, Wanchai and other areas.

But in Singapore, the rebuilding of ageing properties has resulted in modern and generally new-looking houses and apartments.

Land here is scarce and, short of reclaiming more land at exorbitant cost, the solution is to intensify land use and build higher.

There is an economic factor, too. New buildings will stimulate consumer spending on renovation works, new furniture and household appliances.

Also, while commercial buildings built of solid stone and granite may last 100 years, older residential buildings made of cheaper and less robust materials and with inferior technology will not.

Anyone living in an apartment block will have experienced neighbours doing renovation - whether full works on a newly bought unit or partial renovation to replace leaking water pipes and faulty electrical cables.

Apartments on the top floors can suffer from water seepage, sometimes just years after new waterproofing is laid.

Even newly completed condominiums are known to spring leaks in the basement carparks or experience water seepage from the windows.

How will these buildings fare 20 years down the road?

That said, I do agree that it is a waste of precious resources to knock down relatively new and perfectly good buildings for the sake of a windfall.

Perhaps the Urban Redevelopment Authority can tweak the law and ban collective sales for buildings under 20 years old, unless there are extenuating circumstances, such as major structural defects.

For older buildings, tweak the proportion of owners that must consent before a sale is allowed.

For instance, 80 per cent for 20-to 30-year-old buildings, 70 per cent for buildings that are 30 to 40 years old, 60 per cent for those that are 40 to 50 years old, and 51 per cent for buildings above 50 years old.

Matthew Chang