How does HDB decide on number of lifts for a block?

Is there some formula that the HDB uses to work out the number of lifts there are in a block?

Good lift design plays a critical role in the quality of life in high-rise buildings.

I would have thought that the rule of thumb is the more dense the population, the more lifts that would be needed.

However, the number of lifts provided in new estates are fewer than in the older ones, it appears.

For example, in Keat Hong Mirage, there are two lifts for about 168 units in a new 22-storey Build-to-Order block.

In contrast, just one street away, Block 121, Teck Whye Lane has two lifts for 80 units in the 11-storey block which was built in 1989.

In most HDB blocks, there is a greater demand in the morning than in the evening, as people leave for work and school around the same time.

In blocks like those in Keat Hong Mirage, if one (or all) of the lifts break down, the remaining lift's capacity would be insufficient to deal with the demand.

Manfred Lin