"The results are extremely positive and show that a real difference can be achieved. With sustainable construction being increasingly driven by initiatives such as the Code for Sustainable Homes and Site Waste Management Plans, using more of these construction methods means contractors will be able to further improve against waste reduction targets"
Mervyn Jones, Programme Manager for Waste Minimisation and Management at WRAP
Banbury, Oxon, England: A series of case studies published by WRAP (Waste & Resources Action Programme) has revealed that some off site construction (OSC) systems can reduce on-site waste by up to 90 per cent.
The waste minimisation and recycling enabling organisation, WRAP, says that this is an important step in equipping the industry with the knowledge they need to deliver the Government’s proposed target, contained in Waste Strategy 2007, to halve construction waste to landfill by 2012. The studies were commissioned earlier this year.
OSC is growing in popularity for the benefits it offers in terms of time and cost predictability, health and safety, and skills. It has a potentially significant role to play in the delivery of affordable housing and in helping to achieve standards such as the Code for Sustainable Homes.
Construction methods off-site, effectively move construction site activities into a controlled environment where production line processes allow manufacturers to achieve high quality standards, high productivity and importantly better overall waste minimisation.
Case studies
The case studies were undertaken by Mtech and investigated five OSC systems. Mtech worked with some top names in the industry including Framing Solutions, Yorkon, Bison and Stewart Milne.
The systems looked at covered light steel frame, volumetric construction, precast, volumetric pods and timber frame.
Light steel frame (LSF)
The researchers found that the design and manufacturing process of LSF wall panels and floor cassettes borrows techniques and approaches from the automotive industry.
In this way the principles of a lean process are adopted with “just-in-time” deliveries, optimisation and rationalisation of the use of materials. The net effect is a better and more accurate design, a well managed procurement chain, and a significant reduction of wasted resources and materials, according to the report authors.
This system was found to have the potential to substantially reduce the amount of wasted resources and materials by between 40 to 70 per cent.
Volumetric construction
Volumetric construction is widely used for temporary and permanent buildings. Projects covered include housing projects, hospitals, hotels, student accommodation and office buildings. The authors’ say that design and manufacturing processes allow better control of the flow of materials and ensure that the resources necessary for the construction of modules are efficiently used. Integrated design, procurement and management can help to significantly reduce the amount of waste sent to landfill.
The study says that this is among one of the most effective off-site methods and is the only one to bring the trades into the factory to work in a controlled factory environment. This leads to a reduction in potential waste arisings from errors, accidents or snagging and is said to reduce site construction waste by up to 90 per cent.
Precast
Under this OSC system, waste is avoided by ensuring that any fabrication errors are identified at the design stage and that waste reduction techniques are implemented prior to manufacture and construction on site, leading to a reduction of site generated waste by up to 50%.
Precast concrete manufactured off-site have been widely used for structural and ornamental elements in a wide variety of projects, from railway sleepers to bridge elements, housing and stadia.
Manufacturers can produce standardised products using pre-set forms and shutters that are repeatedly reused. An added benefit is that there is a saving in on-site use of temporary supports and scaffolding that are common on conventional construction sites.
Volumetric pods
Volumetric pods are used for such items as bathrooms and kitchens and are transported to site contained in a protective layer of polythene. The research found that this helps to improve construction times and can reduce waste generated by a traditional construction process by up to 50 per cent.
The pods are increasingly being used for projects, which feature design repetition as they optimise the use of materials and generate little site waste other than the polythene wrapping.
Timber frame
The use of timber frame as a replacement for the inner structural layer of the exterior wall is growing in the UK. Its use can reduce construction waste by between 20 to 40 per cent as it is manufactured in a protected and quality controlled environment and reduces the amount of unnecessary materials on site.
Timber frame construction techniques are well understood by the UK construction industry and frequently adopted for residential and small institutional and commercial buildings. The market for timber frame is mainly in low and medium rise buildings (up to 7 storeys), according to the research study.
The simplicity of timber frame construction allows mass production of wall panels and floor cassettes.
Mervyn Jones, Programme Manager for Waste Minimisation and Management at WRAP, commented:
“We recently undertook a scoping study into the opportunities for waste reduction that OSC offered the industry. These five studies provide practical examples of how and where each system can really save on waste.
“The results are extremely positive and show that a real difference can be achieved. With sustainable construction being increasingly driven by initiatives such as the Code for Sustainable Homes and Site Waste Management Plans, using more of these construction methods means contractors will be able to further improve against waste reduction targets.”
Further information
For further information on the waste savings offered by using OSC systems, visit the WRAP website or call the business helpline on 0808 100 2040
Established as a not-for-profit company in 2000, WRAP is backed by substantial Government funding from Defra and the devolved administrations in Scotland, Wales and Northern Ireland.
More information on all of WRAP’s programmes can be found at www.wrap.org.uk