HDB is an early adopter of prefabrication technology. We first used precast components for the construction of flats in the 1980s. Today, for every HDB residential project, precast components constitute approximately 70% by volume of the entire structural concrete used during the construction stage.
Precast technology enables building components to be manufactured off-site, delivered and assembled on-site, providing distinct advantages such as better quality control, safer work environment, and lower dependency on manual and unskilled labour. This has not only increased the quality and safety of public housing, but also reduced construction waste, noise and dust levels, while minimising inconveniences to residents living nearby.
With the technical experiences gained over the years, HDB has been able to develop its own brand of precast technology, known as the HDB Precast Building System. It is an array of 2D precast components combined to form the entire building system. This is the foundation for further R&D studies and advancements into more integrated and complex 3D precast technology.
Prefabricated Prefinished Volumetric Construction (PPVC)
HDB is currently advancing its precast technology into more complex and integrated components. For example, HDB pioneered the concrete Prefabricated Bathroom Unit (PBU), which will be implemented in 85% of the dwelling units to be launched in 2018. Moving forward, HDB will implement PBU to 100% of dwelling units to be launched in 2019, where possible.
Currently, HDB is working to fine-tune concrete Prefabricated Prefinished Volumetric Construction (PPVC), which was first piloted at a housing project in Yishun. The PPVC involves fabricating 3-dimensional modules of whole rooms to reduce work on site. These modular units can be combined in different configurations to create different flat layouts. HDB aspires to implement PPVC progressively, while building up construction capability and capacity. Around 33% of the dwelling units to be launched in 2019 will be constructed using the PPVC method.
The key benefits to using PPVC include:
- Higher efficiency
- Components pre-assembled off-site allows closer supervision of workmanship, minimises wastage of materials, and reduces the need for hoisting of raw materials onto elevated blocks under construction. Construction time on the worksite can be reduced as the fabrication of the modular units can proceed off-site in factory while other worksite activities are ongoing.
- Reduced need for manpower on-site
- Components fabricated off-site reduce the need for workers on-site
- Better construction quality
- The incidence of wet construction joints will be reduced, thereby improving water tightness of wet areas. A lowered dependency on manual labour also translates to more uniform and better quality workmanship.
HDB has introduced flexible loop connectors in facade connection to replace traditional loop steel connecting bars in precast component production.
By adopting flexible loop connectors, the number of connection bars required will be reduced from 18 to just 8 per facade. They also make the fabrication of modules faster and speed up the installation process. Flexible loop connectors are more efficient compared to traditional loop steel connecting bars and have improved productivity in precast components production and site installation.
Smart Base Mould
HDB flats have architectural features such as fins, window designs and groove lines to enhance the aesthetic of the buildings’ facades.
These fins and canopies also help to serve as sunshades, and prevent splashing of rainwater.
Smart Base Mould for precast facade comes with adjustable side forms and block outs to cater for fins of different size, canopy and coping of different lengths. The Smart Base Mould can be shared across projects, and the reusability of these moulds improve production lead time at the precast plant.
Prefabricated Mesh and Cage
Due to high level of standardization of design, Prefabricated mesh and cage are widely used at HDB projects.
It is a comprehensive system of factory pre-assembled steel meshes and cages. The checking of sizes and spacing of these reinforcement are greatly simplified.
Hollow Core Slab System For Multi Storey Carpark
The use of hollow core slab system eliminates slab scaffolding works, as it can span from beam to beam.
The elimination of scaffolding works leads to manpower savings. In addition, site safety will be enhanced as work-at-height activities will be reduced.
Automated Precast Production System (APPS)
The Automated Precast Production System (APPS) makes use of advanced Computer Aided Design and Manufacturing Technology (CAD-CAM) to automate the production processes.
HDB has developed a wide variety of customised precast components designs, such as the Large Panel Slab (LPS), Precast Sandwich Wall and Precast Flat Slab systems that leverage APPS technology for production.
The LPS can be produced in large panels or custom-made room-size precast floor panels, thus reducing the amount of site handling and carpentry works by about 30% and enhancing the productivity of floor construction by 20%.