Offsite momentum puts precast in prime position
With growing momentum behind the use of offsite manufacturing, precast concrete firms see their experience and the sector’s tight regulation as an important USP. Will Mann reports.
Prime mover advantage is important in any new or growing market. And it could be a significant advantage for precast concrete, now that offsite manufacturing is back in vogue, with the government promising to favour the technology on public projects from 2019 and the Greater London Assembly proposing an offsite providers framework.
“Precast concrete has been around a long time, and most of the construction industry understands how it works,” says Andrew Minson, executive director at The Concrete Centre and British Precast.
“But with many other offsite products, there is a degree of risk because they are new. Project team members may be wary of being early adopters of new technology and being exposed to new suppliers.
“There are questions over the long-term performance of these products, how robust they are during transport and assembly on site, how they perform in fire, whether they are compatible with the foundations.”
Those concerns are not present with precast, Minson reasons. “For example, precast structural elements can be designed and constructed seamlessly with insitu concrete foundation,” he says. “In the precast sector there are long-established skills, processes, design codes and standards – and these are continuously evolving and being updated.”
Minson points to the newly updated BS 8297, which covers precast cladding (see box p30), and also the new code of practice for safe installation of precast concrete flooring and associated components, published in November.
“This code of practice is not a sales piece, it’s vital information for industry professionals, which the Precast Flooring Federation (part of British Precast) has worked on with the Health & Safety Executive (HSE),” says Minson. “The HSE sees this as an important directive, because so much precast flooring installation involves working at height with heavy plant.
Creagh’s Rapidres system has been deployed by developer Dandara
“It’s the fourth version of this code of practice, and it takes into account the Construction (Design and Management) Regulations 2015 – which shows how prompt the precast sector is at responding to changes in other industry regulations.”
With a positive mood pervading the precast sector, many of Minson’s members are finding clients increasingly keen to work with them and move more of the onsite construction processes into the factory.
One of these is Creagh Concrete, headquartered in Antrim, Northern Ireland, and with locations in Edinburgh and Nottingham. One of its biggest clients is developer Dandara, which has taken a “far sighted” view on the potential benefits of precast, explains Creagh director Ian Brogan.
“Dandara is leading the housebuilding market in use of precast,” he says. “They have taken a view that it can offer improved speed and quality in delivery compared to traditional construction.”
The developer decided three years ago to use one of its projects, the 276-apartment Stoneywood scheme in Aberdeen, as a trial to test the benefits of precast, Brogan explains.
Creagh was appointed to design, manufacture and assemble the precast elements of the project on site, using its Rapidres fast-track building method.
FP McCann has a £5m package at the Lansdowne, Birmingham
“Dandara regarded the Aberdeen project as a learning curve for themselves, with the aim of continuous improvement from project to project,” says Brogan. “Their philosophy is to maximise use of offsite construction across all elements of the project, and achieve quality of 100%. This obviously saves on any alteration work on site.
“There was no principal contractor on Stoneywood. We supplied and installed all the precast components, and Dandara managed construction of the foundations, fit out and building services.”
At Stoneywood, Creagh supplied the complete frame, comprising precast cross walls and hollowcore flooring, plus an external facade of acid-etched and brick-faced sandwich panels, all manufactured in its factory. Telecoms and electrics were cast into the precast panels, plus ducting, vents and openings for mechanical services.
The site programme was completed in just 50 weeks. “This was obviously a major benefit to Dandara, who would likely have run into weather-related problems using bricklayers and scaffolding in Aberdeen during the winter,” says Brogan.
Creagh has now moved on to another Dandara project, the Arena Central scheme in Birmingham, where it is again using the Rapidres system.
Brogan believes one of the firm’s biggest selling points is its “turnkey” solution. “We design projects in-house, and employ 180 professionals including estimators, engineers, planners and project managers,” he says. Creagh’s total staff numbers over 600 including the manufacturing plant.
FP McCann’s precast panels in its factory and (below) its installation team on site at the Lansdowne
Brogan expects digital technology to play an increasing role. “We work with Revit and use 3D modelling,” he says. “Our more experienced draughtsmen will design the main structure of the building, and then as we develop the model, individual elements are extracted and designed in Revit.
“In Creagh’s academy, we will start providing training on BIM in-house next year. The long-term goal is to digitise how we feed information into the factory and move towards a more automated manufacturing process.”
Another Northern Ireland firm expanding rapidly is FP McCann, the UK’s biggest manufacturer and supplier of precast products, which has its head office in County Londonderry. The firm, which raised eyebrows a year ago when it bought Laing O’Rourke subsidiary Bison’s Uddingston factory, is investing £12m in four of its dozen manufacturing plants, according to marketing manager Kieran Fields.
Like Creagh, FP McCann is also investing in BIM. It won a Tekla UK BIM Award for its “development dock”, where parametric control is used for the detailing of precast components. “We are now seeing projects where all the key precast components are designed in BIM,” Fields says.
One of FP McCann’s biggest current projects is a £26m development in Birmingham, The Lansdowne, a 16-storey, 206-unit residential apartment building, where Interserve is main contractor. FP McCann has to date supplied and installed over 1,500 precast units to form the structural frame, floors and lower to middle level decorative cladding envelope.
The supporting structure comprises external sandwich panels and internal precast concrete walls, with the facade panels accommodating two-storey high windows, plus columns and beams which support the steel framework for the fixing of precast hollowcore planks.
“All vertical precast wall sections have been designed for ease of build, linking together with hidden tie rods,” says Fields, adding that joints are finished with a high-strength non-shrink grout, which meets building regulations.
“Both the structural and architectural facade teams at FP McCann worked closely with designers SRC and architects Building Design Group to ensure the manufacturing of the components met the specification standard.”
The planks were supplied from FP McCann’s Weston Underwood production facility near Derby while the facade panels were manufactured at its architectural precast facility in Byley, Cheshire. Fields says a nationwide network of plants is not only important for servicing regional markets, “it also helps with sustainability because transport distances are reduced”.
This environmental credential is important, believes Minson. “Precast concrete is a local product,” he says. “The majority of precast used in the UK is made in the UK. This also reduces the risk from exchange rate fluctuation, transport problems, communication problems and difficulties in inspecting products prior to leaving the factory.
“Our members provide responsibly sourced products, accredited by the BRE BES 6001 scheme and the British Precast charter for sustainability,” he adds.
Raising the standard for precast cladding
The revised BS 8297 modernises guidance on design, manufacture and installation of concrete cladding.
BS 8297, the standard which covers the design, manufacture and installation of architectural precast concrete cladding, has been updated and the new version was published in October 2017.
“It has been revised to account for changes in manufacturing techniques and product ranges introduced over the last 20 years,” says Luke Smerdon-White, technical director at Thorp Precast, who worked on the committee which carried out the revision.
“The last update was some 17 years ago and reflected some practices, details and materials that are no longer used within the industry. The Eurocode BS EN 1992 was issued in 2004, which superseded previous codes referenced within BS 8297.”
“There are methods for testing the durability of brick slips and tiles with minimum ‘pull-off’ values to be met.”
Luke Smerdon-White, Thorp Precast
New precast facade classifications, types and finishes have been introduced, meaning that a wider range of products can be specified and manufactured to a relevant British Standard. These include cladding, linear elements, precast sculptures and other aesthetic features.
One recommendation of the new BS 8297 is early engagement of the precast concrete specialist.
“This is paramount for the project team’s understanding of the building’s movement and tolerances,” says Smerdon-White.
“Only with an early and clear understanding of these can the technical requirements and visual aspirations be assessed.”
Quality is another key part of the revised standard. “One section details the performance testing requirements of the panels when applied in a building envelope, and the minimum standards to be met,” says Smerdon-White. “Additionally, there are recommendations for panel inspections and viewing distances.
“BS 8297 also addresses the materials used to face precast panels, such as brick, stone and tiles. As an example of this, there are methods for testing the durability of brick slips and tiles with minimum ‘pull-off’ values to be met.”
The standard is intended to be used in conjunction with the precast common rules standard, BS EN 13369, and the execution of concrete structures standard, EN 13670. BS 8297 is also compatible with the Eurocode suite of design standards.
Members of British Precast Architectural and Structural who worked on the update include Andrew Tyrrell, managing director at Decomo, and Tom Salmon, preconstruction manager at Techrete. Facade consultants FMDC and Wintech also contributed, along with the NHBC and Charles Goodchild, principal structural engineer at The Concrete Centre.