First generation – Basic design (1960-1966)
The houses were simple slab blocks with exterior corridors. With only one layer of flats being lined along the corridor, each flat was designed to allow cross-ventilation. The principle façade usually faces north-south but the rule was not strictly followed.
Second Generation – Introduction of built form variety (1967-1976)
Height variations were introduced in order to provide more space on the ground level therefore enabling recreational facilities and maintaining the high density of public housing.
In relation to the building and open space, the blocks were aligned in terms of their shapes, heights and positions to create a right enclosure to ground space and also to control the natural lightings.
In addition, void decks were introduced to free dwelling units in 1969. Hence, these ‘void decks’ can be used for other purposes such as shops.
Third Generation – Built form as a means for holistic urban design (1977-1981)
At the level of the precinct, clusters of buildings focus on an activity centre including a children’s playground, games courts and play areas. This gen also emphasized on intermixing the low and high buildings which allows more varied spacing between buildings and the creation of a variety of interesting space.‘Built form’ was also used in the purpose of noise reduction. Lastly from this gen, to create functional and easily identifiable precincts, the site plan of HDB housing was laid out in a checkerboard pattern.
Fourth Generation – First Intensification of land use (1982-1990)
Layouts of residential precincts were made more compact by adopting closer spacing between buildings. The buildings in cellular layouts in smaller clusters of 3 to 4 blocks of buildings comprising a total of 400 to 500 dwelling units instead of 600 to 1000 units applied in the previous generation.
Layout plans in this generation were more rigid and orthogonal, thus tightening of spacing between buildings to increase development intensity and to achieve the new “cell” concept.
This generation end with the adoption of a system of classifying high-rise buildings based on location and urban design principles. The first category consists of special designs for building in good locality and with an excellent view such as those facing the sea or reservoir and those situated at the entrances to new towns, at town centres and at neighbourhood centres. The second category consists of designs for buildings with distinctive forms and located along the perimeters of expressways, major roads and vista points. The third category consists of buildings with basic prototype designs.
Fifth Generation – Diversification of design and designers (1991-now)
The Design-and-Built Scheme in 1991 and the Design Plus scheme in 1995 were introduced. HDB was no longer the sole planning and architectural designers of HDB housing. In 1991/92 under the Design-and-Built Scheme, HDB sets aside land within its new towns for private architects, engineers and contractors to design and build public housing in order to give home buyers a wider choice.
Design diversity was further enhanced in 1997/98 when housing construction under the Punggol 21 plan commenced. One-third of all public housing would be Design-and-Build flats, another one-third would be Design Plus flats, and the rest would be standard HDB flats.
Sixth generation – Further increase in building height and density (1999-now)
This generation is demarcated by further increase in development intensity and building height. To further optimise land use, a feasibility study was carried out to investigate the possibility of building taller HDB apartment blocks. The first 40-storey apartment block was tendered in Toa Payoh in December 2000. The higher plot ratio was achieved through efficient site layout and compact block configuration built to the permitted storey height. Urban Design Framework for new and old towns was formulated to provide directions for the design of the built environment (HDB AR 2005/06). With the Urban Design Framework, it was hoped that consultants would be guided to develop schemes that fit the overall urban design intentions of the town.