King’s Cross’s iconic gas holder is about to be joined by a more discreet example of technical innovation: Shepherd Engineering Services’ prefab ‘cupboards’, which are transforming the laborious business of M&E installation at a new residential block. Stephen Cousins reports.
Perhaps the most iconic structure on the 67-acre King’s Cross redevelopment in Central London is the 25m-high cylindrical frame of Gas Holder number 8, a symbol of Victorian engineering ingenuity that until 2001 stored much of the gas needed to provide heat to London. The highly decorative grade II-listed wrought iron structure was recently refurbished by a specialist engineering firm in Yorkshire and reassembled on the north side of Regent’s Canal.
But right next to it is another, more contemporary, example of British engineering excellence. The £80m Plimsoll Building, also known as P1, is the third residential block to be built on the site. Designed by David Morley Associates, and due for completion in autumn 2015, its interior is a showcase for the latest offsite manufacturing techniques, while the exterior is clad with hybrid prefabricated brick and precast concrete panels.
Main contractor Carillion is delivering its three inter-linking 14-storey towers with 255 apartments, integrated with a primary school and a school for the deaf on the ground and first floors. Meanwhile, Shepherd Engineering Services (SES) is responsible for the £13m services package, working with Carillion’s design team to develop a modularised riser system, as well as a service “cupboard” for each of the flats, incorporating heat, power and plumbing systems within a metal frame that is
simply dropped into position.
“We know the layout of pipes and ducts in each riser module will connect precisely to the level above because everything has been built to the same specification.”
Ian Cordery, Carillion
By modularising the services, SES has been able dramatically to reduce the number of trades needed on site, as well as cutting 15,500 man-hours on site to meet the construction programme.
This provides several knock-on benefits for Carillion, explains project director Ian Cordery: “Installing the MEP [mechanical, electrical and plumbing] cupboards and services risers as we build up the structure gives us programme certainty and improves quality, because every unit is built in a dry factory environment.
“It has improved safety because there is less need for multiple trades on site, and there is a greater consistency to the finished article because the detailed design has not been interpreted differently by different tradesmen. For example, we know the layout of pipes and ducts in each riser module will connect precisely to the level above because everything has been built to the same specification.”
The completion of the Plimsoll Building will signal another milestone for the King’s Cross development, which is set to transform the heart of central London with the creation of 50 buildings, 2,000 sustainable homes, 20 streets and 10 public squares. P1 has 178 private apartments, of which 134 are “classic” flats with underfloor heating and high-specification finishes, 38 are “premier” apartments with the addition of air-conditioning, and six are penthouses with larger living spaces and impressive views across London.
One of the building’s three towers will house 77 affordable homes for key workers, provided in partnership with housing charity the Dolphin Square Foundation. The two schools are a two-form entry academy primary school with a 26-place nursery attached, and the Frank Barnes School for Deaf Children. They will share facilities within an integrated, inclusive and signed/spoken bilingual environment on the ground and first floors. There is also a 100 sq m retail unit and a community meeting space on the ground floor.
As the design-and-build contractor, Carillion was quick to identify the programme certainty and health and safety benefits associated with offsite manufacturing. It urged King’s Cross Central Limited Partnership (KCCLP), the developer of the scheme, to allow it to work with subcontractors during the early design stages to maximise the use of offsite fabrication.
“Key to the project’s success was KCCLP’s willingness to pursue prefabrication and allow us to get suppliers, particularly SES, onboard early in the design to maximise the amount of offsite prefabrication,” says Cordery. “We always push to use as much prefabrication as possible, which helps everyone in terms of consistency, quality and programme certainty, but it always depends on the client’s understanding of the benefits of prefabrication and willingness to go down that route.”
“We were able to install a complete riser in a single day. Using conventional techniques it would have taken eight trades three to four weeks, or longer, to produce.”
Will Newman, SES
SES previously worked with Carillion to deliver modular services at One St Peter’s Square, a 14-storey office block in Manchester city centre, completed earlier this year. But it wanted to try something new at King’s Cross. “Offsite manufacture is embedding into the business’s DNA; if our project managers don’t want to use it they have to provide us with justification,” says David Mason, executive business director of SES. “We encourage our designers to be entrepreneurial about how they develop solutions and expand our capabilities as a company.”
One such entrepreneur is SES project manager Will Newman. He was the man who, in collaboration with the detailed design practice Weedon Architects, came up with the idea for a service cupboard that incorporated M&E plant and equipment. Each steel-framed cupboard module is roughly the height of an apartment and concealed within a partition wall, behind a pair of double doors. It incorporates a heat interface unit, a heat recovery unit, underfloor heating manifolds, consumer unit, BT Home Hub and has enough space left over for a washing machine.
The cupboards are produced by SES’s modular manufacturing arm SES PRISM and delivered to site shrink-wrapped in batches of 15 per lorry. The frames are fitted with stiffening bars to prevent any twisting during transport, and they have wheels, so that once hoisted up the building, they can be rolled across the concrete floor slabs to the flats. Once in position, they are jacked up, the wheels are removed, and they are lowered into position.
“It was a revolutionary concept to combine all the MEP work for a cupboard, right down to internal finishes, in a single prefabricated framed unit. It provides us with a final-fix item that is pre-wired and pre-tested ready to be plugged directly into the building services at ceiling level.”
SES PRISM also modularised the main service risers for the building’s seven riser shafts, each extending over 50m and incorporating 3km of finished and tested pipework, ductwork and electrical containment. The shafts are divided into 10.2m-long riser modules, each three storeys in height – the maximum transportable by PRISM’s lorries. Working in a riser several floors up usually involves numerous health and safety challenges, but SES’s modules incorporate a welded-steel chequer plate floor with integrated kick plates, making the unit safe to stand on from the moment of installation.
Above: The view of St Pancras Station, as seen from the flats. Below: SES was able to cut 15,500 man-hours on site by modularising the services
“The risers were dropped into position as the cast insitu frame progressed,” says Newman. “We were able to install a complete riser in a single day, roughly a couple of hours per section, whereas using conventional techniques it would have taken eight trades three to four weeks, or longer, to produce.”
Early design engagement and prefabrication techniques employed by SES are expected to save 15,500 man-hours on site, calculated as 10,500 hours for the MEP cupboards and 5,000 hours for the risers. Because the risk of constructing a residential block lies in the time-consuming completion of the apartments, requiring numerous handovers, and separate testing and commissioning, completing the services early will enable that work to start earlier than envisaged.
Reliance on offsite manufacture has led to improvements to onsite safety. As proof of this, SES has notched up five million hours without a reportable incident or accident on any site, which it puts down to the need for fewer trades and less waste on site, which in turn means fewer slips, trips and falls.
Saving time and resources has also had a benefit in terms of cost savings, but this hasn’t necessarily been realised in SES’s profit margin. SES’s David Mason explains: “Using innovations creates surety of delivery and reduces incidents and accidents on site, thereby ensuring the costs for all concerned on the project are protected. That way, everyone’s profit is realised and not eroded by old and poor practices.”
As the Plimsoll Building approaches the halfway stage, SES is turning its attention to early designs for the Triplets project, a high-end apartment complex to be built inside the frames of King’s Cross’s other three gas holders, which are currently being refurbished to be installed on the site adjacent to P1.
Here, Newman has his eye on further innovations. “These flats are likely to have more advanced modules fitted with wireless communications for apartment controls, allowing occupants to run heating systems, or bathroom or kitchen appliances using a tablet or a smartphone from inside the home or even from their car.” It’s an engineer’s vision of the future that the Victorians would be proud of.
The high-tech Victorian panels
The building’s architecture references Victorian heritage, with external cladding designed to replicate the textured brick seen on several buildings on the King’s Cross site, such as the restored warehouses of the Central Saint Martins art school. The external facades were planned as traditional brickwork, but Carillion was able to demonstrate to KCCLP that a hybrid precast system, fabricated by Thorp Precast in Newcastle-under-Lyme, would deliver a similar result in terms of aesthetics and performance, for less money.
Each 7m-wide bay has four or five cladding panels weighing between three and six tonnes. The panels incorporate traditional bricks, each made with a special rebated detail at the back that is designed to key into the structural concrete.
Once panels are cast, they are pointed in factory conditions to achieve the correct colour and texture. “There is always a concern with precast that the joints between panels will be visible on the envelope,” says Ian Cordery, Carillion’s project director. “But this facade has been deliberately designed with raised and recessed features to divert the eye away from any repetition, while still minimising the number of panels.”
