Permanent Formwork

uPVC Wall Construction Systems

New generation concrete-filled PVC stay-in-place (SIP) formwork wall construction systems have been developed in Australia to offer significant benefits in terms of construction timeframes, life cycle costs and embodied energy performance. The permanent formwork is eligible for a Responsible Building Materials credit under the Green Building Council of Australia’s Green Star rating tool.

Innovative Australian companies are producing modular SIP systems with proprietary components such that different brands of formwork have different connecting moulds and systems. These new systems can be used to replace load-bearing conventional precast concrete, tilt-up or masonry block walls and are today used for basements, stair and lift shafts, blade columns, irrigation tanks, retaining walls and other areas, and in buildings 30 storeys high.

Traditional, temporary formwork using timber, plywood or steel is labour intensive. The approach can represent 40 to 60 per cent of the total cost of a concrete structure. Glass-reinforced plastic, fibre-reinforced plastic, thermoplastics (PVC, polystyrene), fibre cement and metals are examples of materials used to pre-fabricate formwork for permanent systems where the materials remain in place for the life of the building. The components can be interconnected to create formwork that can be erected with a high level of efficiency.

While concrete is generally used in construction for its high compression strength, its drawbacks include the need for reinforcement with rebar to compensate for its poor tensile strength, its propensity to crack under sustained pressures such as in basements and retaining walls and its porosity which can lead to 'concrete cancer'. Using SIP formwork helps overcome these problems as the concrete is sealed or protected from the environment by the formwork for the life of the building. The connectors in the latest SIP formwork systems facilitate concrete flow and consolidation and there’s usually no need to vibrate the concrete.

In the case of thermoplastic SIP formwork, the interlocking system of the modules completely seals the joints and the polymer effectively acts as a waterproofing membrane, a feature that can be particularly beneficial for basement walls. Some systems allow a reduction in the quantity of cement required, and an increase in the amount of fly ash or aggregates used as a substitute without raising concerns of concrete cancer.

These technical aspects of permanent formwork systems have been shown to have the potential to reduce the environmental impacts as well as health and safety risks on construction sites. Some of the latest SIP formwork systems reduce the quantity of steel reinforcement required, playing a significant part in reducing materials consumption and, importantly, the embodied energy of the built form. In addition, there’s no need for stripping SIP formwork, which together with their light weight and ease of installation can improve health and safety on site and reduce injury risk.

However, because of their light weight, some modular systems can be more susceptible to wind load during installation and before fixing; they may need bracing before the concrete pour. It’s also critical to ensure that any modifications to a SIP formwork system’s mould design or the use of a combination of two systems’ components is checked and signed off by suitably qualified people because of the proprietary, and therefore differing, nature of systems in the market.

Companies using SIP formwork cite cost savings, construction time savings and ease of installation as key attractions to the systems. The decision to use permanent over traditional formwork or masonry work can also be driven by site requirements, particularly where there are water issues and retaining wall requirements; and project design requirements such as multi-storey underground basements.

From an environmental and safety perspective, SIP systems have been shown to benefit projects through transport energy savings, significant reductions in embodied energy of materials, better site safety and reduced long-term maintenance. Some of these systems have also been certified to meet earthquake and bushfire requirements and can therefore contribute to the need in Australia for a more resilient built environment.