The update to RIBA’s Overlay comes five years after the original, but why is it needed and what design considerations does it recommend as MMC projects move from earliest concept to handover and operation?
Interest in offsite construction is gaining momentum, as evidenced by government backing and a recent spate of investments and contracts, but if the industry is to fully capitalise on the benefits of prefabrication (faster delivery, programme certainty, improved quality etc.) then it must also reform the way projects are designed and procured. Those in the know emphasise the need for early engagement with offsite manufacturers and consultants as too often architects consider MMC solutions too late in the design process and must then go back to the drawing board to adapt designs for offsite products, resulting in programme delays and increased costs.
The DfMA Overlay to the RIBA Plan of Work was introduced in 2016 to help overcome this and related issues by setting out what architects, designers and others involved in construction projects should do at each stage of the project lifecycle. The new edition of the overlay, developed by a group of industry experts supported by Akerlof, Buildoffsite, Kier, Supply Chain Management School and UK Research and Innovation, aligns with the RIBA Plan of Work 2020 and also accommodates the new definition of the seven different categories of MMC, plus recent advancement in BIM and other digital construction tech.
Major commercial players are already investing in MMC factories and innovative processes, encouraged by the Government’s presumption in favour of offsite manufacturing as stated in the Construction Playbook and Value Toolkit. The Overlay sits alongside a raft of other publications intended to boost the sector, including the Government Infrastructure and Projects Authority’s "Transforming Infrastructure Performance: Roadmap to 2030", and incorporates a detailed report giving an overview of the industry’s rapidly maturing market readiness. The report explains, among other things, what DfMA is; the close ties with digital technology; how designers and project teams need to work differently; practical advice on early stage optioneering - considered critical to success - and why procurement need not be a barrier to using DfMA.
In his preface to the report, Mark Farmer, the UK Government’s MMC Champion for Homebuilding, explains that the Overlay is an important step forward because it shows clients and their teams how to set up projects from strategic definition stage onwards, which “has a massive impact” on the success of adopting manufacturing principles and effective deployment of MMC. Apart from the need to define DfMA building systems and technologies, he says “there was a need to define the process by which you enable the optimisation of MMC”, which relies on the correct approach to client project management. This spans “from setting initial client requirements, integrating the team with the appropriate procurement mechanism and front-loading key decision-making to driving discipline in avoiding unnecessary client change,” says Farmer.
Furthermore, in a world where insurers and funders will increasingly want better digital verification of assets, Farmer says the Overlay supports the creation of a digital thread of information, from design through to manufacture, assembly and construction, and on into operations. “There will be an increasing need to use technology to be scalable and assured as opposed to just transferring on-site process failures into factories,” he says.
DfMA in detail
The overlay itself outlines the strategic outcomes, core DfMA tasks, suggested digital tasks for DfMA and procurement strategy for each of the seven RIBA Stages.
Windows of opportunity for DfMA procurement vary through the seven different RIBA stages, the document states, also depending on the different project roles and the category of MMC being considered. For example, it may be possible to decide on large-format category 6 cladding systems as late as RIBA Stage 4, but Category 1 solutions will need to be considered from RIBA Stage 2 to prevent costly redesign and programme delays.
By the end of RIBA Stage 0 - Designers and consultants should have identified the best means of achieving the client requirements. To reach this point, they should consider opportunities to apply the seven MMC categories across portfolios or programmes of projects, as well as how DfMA might impact on the business case or client requirements, including opportunities for repurposing and reuse of the building and components. Data from previous DfMA projects should be analysed to set benchmarks, including for cost and programme.
RIBA Stage 1 - A project brief should be produced and approved by the client with confirmation that it can be delivered on the site. DfMA-related tasks should cover, among other things, efforts to identify DfMA opportunities to repeat elements on future projects and how to incorporate the seven MMC categories into the project brief and project programme.
R&D with manufacturers should determine supply chain capability and designers should consider DfMA solutions and best practice exemplars when carrying out feasibility studies. Different MMC categories will also impact on the set up of the project team, including the responsibility matrix and professional services contracts, so this must be given due thought. The use of BIM is recommended to prepare feasibility studies and teams should consider using a digital library with DfMA objects and components and its potential use across multiple projects.
RIBA Stage 2 - The architectural concept should be approved by the client and aligned to the project brief. Appropriate MMC categories should be embedded into the architectural concept, while the cost plan, construction, sustainability, the plan for use and Health and Safety strategies should all take into account DfMA. Also worthy of consideration are strategic engineering aspects, including floor-to-floor heights, spans, space requirements and foundation design should all be considered.
Digital information should be developed to include data-rich DfMA content, possibly from a digital library of Stage 4-ready objects and the BIM model should be validated against the Information Requirements.
RIBA Stage 3 - All architectural and engineering information is spatially coordinated. The construction strategy and cost plan should be updated, taking into account discussions with potential contractors and the supply chain. Teams should consider buildability, including how the erection sequence, fabrication or manufacturing techniques and tolerances impact on interfaces. Warranties for proposed MMC systems should be checked.
RIBA Stages 4 and 5 (which often overlap) - All design information required to manufacture and construct the project and all design information required to manufacture and construct the project is completed.
Teams should consider how DfMA impacts on building systems, including ‘plug and play’ connectors and interfaces. They should develop DfMA components more accurately considering interfaces and specifications including structural, water/moisture/vapour penetration and acoustic issues. The construction strategy should be updated to include a logistics plan that considers lifting, handling and transportation for each component and sub-assembly. The quality of offsite manufacturing and the commissioning strategy need to be monitored.
Digital tasks should cover updates to digital information, including from the supply chain, and validate the model against Information Requirements, potentially using 4D BIM to scenario test and rehearse the sequencing. Software should be used to: track manufacturing, packing, logistics and delivery. Other tools can be used to train site operatives and access digital information, including setting out, method statements or product manuals.
RIBA Stage 6 and 7 - After the building is handed over, aftercare is initiated and the client/ facilities and asset managers ensure the building is used, operated and maintained efficiently.
Teams should provide feedback on defects and on the DfMA process for consideration in future projects. Digital information relating to DfMA components should be linked to feedback, including lessons learned and potential repurposing. Facilities and asset managers should monitor the performance of standardised components, including maintenance and replacement and provide feedback. They should provide feedback on aspects identified for reuse or recycling at the end of the building’s useful life. Configuration management techniques can be used to update digital asset information during the life of the building, and data from in-use activities can be fed into Digital Twins and smart building technologies.