Eliminating The Risks Of Offsite Construction
15 Jun 2017
So you want to choose offsite construction, knowing that project team members are wary of the risks of being early adopters of new technology and being exposed to new suppliers. Precast concrete overcomes these concerns and there are other benefits too.
Precast concrete can be used for all building types and infrastructure projects. It overcomes the risks associated with other offsite construction methods, and it is a local product with strong sustainability and performance credentials backed up by many years of experience. Typical risks of offsite construction are listed below, and an explanation is given of how precast concrete mitigates each risk.
Precast concrete has long established standards for products through BSI and many of these are harmonised across Europe through CEN. Therefore many precast products are CE marked as normal practice. This enables designers and project teams to specify their offsite products with greater confidence. This also equips contractors with the information to receive offsite products with the right quality and performance parameters.
The Eurocode suite of design codes by CEN with UK National Annexes by BSI have now replaced the British codes which have been withdrawn and are no longer maintained. Designers can use these Eurocodes with offsite precast products because the precast product standards and design codes have been developed simultaneously with the purpose of being consistent with each other.
A robust supply chain
The membership of British Precast is extensive with many members producing a wide range of products. This provides project teams and contractors with a competitive supply chain. This is beneficial at tender stage and reassuring so that the project is not reliant on any one possible supplier.
Precast concrete is a local product. The majority of precast used in the UK is made in the UK. This reduces the risk to exchange rate fluctuation, transport problems, communication problems and difficulties in inspecting products prior to leaving the factory.
A responsible supply chain
Society in general is familiar with the concept of fair trade. Responsible sourcing is the equivalent term used within the construction sector. British Precast members provide responsibly sourced products. With the BRE BES 6001 scheme, the British Precast Charters for Sustainability and Health and Safety and all members operating under UK employment laws, clients can fully address risk by choosing from the British Precast supply chain.
Durability/robustness during construction
Is there a better material for ease of transport and delivery to a building site than concrete when it comes to being durable and robust? It does not require the same protection from weather and impacts as lightweight solutions do.
Longevity during operation
The same precast concrete properties of durability and robustness also deliver a low maintenance long lasting offsite solution reducing risks during operation and of client concern over the enduring value of the asset.
Fire resistance during construction
The HSE view is clear - timber frame solutions pose higher risks. The timber industry to their credit has introduced extensive measures to be adopted by clients, designers and manufacturers to try and address these risks. The HSE advises that there is a duty of care to reduce risk through design. This can most effectively be done by choosing concrete and avoiding unnecessary fire load.
Fire resistance during occupation
Government statistics are clear – timber frame solutions have a higher risk of more extensive fires. To address this, the Chief Fire officers are trying to register all new timber framed buildings but the scheme is voluntary. Some local authorities are trying to introduce information plates for buildings which are timber framed. These initiatives highlight the problem and look to mitigate risks, but they do not reduce the potential wider risks to the project team. The choice of non-combustible solutions reduces these risks and those of clients and helps them meet their legal CDM requirements.
The Zero Carbon Hub may have been wound up in 2016, but their warnings to government of the risks of overheating should be heeded. Responsible developers and informed building owners such as Housing Associations are increasingly aware of the major risk of future overheating. With the right design the inherent thermal mass of precast concrete is ideally suited to absorb heat to reduce peak temperatures. This overheating risk is recognised in the building regulations and the benefit of thermal mass accounted for in the associated SAP calculation tool.
Offsite solutions have the disadvantage of requiring a longer lead in period. During this lead in period, onsite insitu concrete works can be carried out; for example, foundations and the ground floor. Insitu concrete and precast concrete can be designed and constructed together seamlessly: same design codes, same material properties and same jointing principals.
With precast concrete offsite solutions, the one-offs can be cost effectively created with onsite insitu concrete. For example, an entrance in an accommodation block or a foyer in a commercial premises may not be suitable for factory production but can be cast onsite as precast elements are installed elsewhere on the project.