Its unique feature: Antique-looking spiral staircases snaking around its exterior.

The staircases are not there for aesthetic purposes, however.

The block's original internal stairwell was gutted to make way for a small lift shaft when it underwent the lift upgrading programme (LUP) in February . As a result, new staircases had to be built. Since there was no room within the blocks, the stairs had to be added to the bulding's exterior.

The HDB said the conventional lift-upgrading solution - building an external lift shaft - would not have worked for the four-storey block.

It has no common corridor joining the apartments, so more lifts had to be installed.

The units are also on so-called 'half-landings', which means that even if an external shaft was built, residents would have had to walk up half a flight of stairs from the lift lobby to reach their apartments.

The block, 186, is the first of six to get similar staircases under the LUP.

Work on the others - blocks 177, 178, 183, 184 and 185 - is expected to be completed in the third quarter of next year.

By the time the project is done, a total of 67 lifts and spiral staircases would have been added to the blocks.

Read the full story in Saturday's editio of The Straits Times.