Home work

November 2004 will see the opening of the new £311 million central London headquarters for the Home Office. Located in Westminster, just a few streets from the Houses of Parliament, the development replaces the former offices of the Department of the Environment, the pantomine-monikered Three Ugly Sisters.

The 1960s buildings have been demolished and replaced by three sleek, high-tech buildings that form the Home Office Central London Accommodation Strategy (HOCLAS). Positioned side by side, the buildings are linked at basement level and by bridges at floors one to four. They are intended to provide a cost-effective solution for the Home Office’s long-term office needs in central London, and staff from several sites around the capital will be amalgamated in the two six-storey and one four-storey blocks.

The project has been constructed under the Private Finance Intiative (PFI), with the owning consortium comprising HSBC Infrastructure, french firm Bouygues UP and its sister company Ecovert FM. Much of its success can be attributed to close working of the construction team and the early involvement of those further down the supply chain.

Early learning

M&E contractor SES became involved early in the process in September 2002 when the design was being finalised. It won the contract for installation and commissioning of m&e and public health services throughout all three buildings by competitive tender and spent the first year based at Bouygues’ main office in London’s Waterloo concentrating on pre-installation work, finalising drawings, procurement and technical submittals.

“We had a lot of input with the design team and Bouygues to come up with value engineering solutions and different methods of installation,” explained SES electrical project manager Peter Edwards. “Flack + Kurtz, who are the consultants, and Bouygues were very forward-looking with respect to new products to the market and innovation.”

SES’ input focused on the selection of methods and materials that were labour-saving and could reduce costs. These included the use of modular wiring in much of the installation rather than traditional conduit and cable; plus copper pressfit fittings on the pipework.

Prefabrication was also used where possible to reduce time on site and increase health and safety: pipework arrived precut and welded with bends in position and preconnected, prewired distribution boards simply had to be connected at the top on site. “All we did was bring along a glorified plug which then plugged into the top of the distribution board. That saved hours of labour tied up in riser cupboards trying to connect up to the distribution boards,” stressed Edwards.

It wasn’t just SES that was involved at this early stage. “The whole team was at Waterloo,” explained Edwards. The design team members all shared the Bouygues office. “When you’ve got shared accommodation it breaks down all the problems with communication and gives more sense of teamwork,” he reasoned.

Subcontractors were on board prior to the move to site in September 2003 and once on site the same principles of close working and shared accommodation were applied: SES shared an office with all of its major subcontractors.

This close working extended to the suppliers and distributors and became a vital ingredient in completing the project. The issue of storage space was countered by materials being delivered to site prepackaged by the distributors on an area and floor-by-floor basis. “What you do is call in levels,” explained Edwards. “All the crates were sealed on pallets, all labelled as to which area it’s destined for – which block, which level – and as soon as it arrives you know where it’s going to go.”

The suppliers were closely involved in this process, from agreeing the order and the logistics, to supplying the materials in the agreed format. Their involvement played a large role in the fast-track process. Edwards elaborated: “The design was changing – especially on lighting – quite considerably, so we had drawings going directly to our lighting suppliers at the same time as I was receiving them.

“They would project manage that, quantify what our requirements were and a lot of it was on trust as well as they would confirm to us what quantities we needed and we amended quantities accordingly. So if there were any changes then the manufacturers knew about it straight away.”

Bouygues operated an E-Doc system in which all documents and drawings were stored on a central database. The project team members could then download this from a password-protected internet site.

Serving the construction

Demolition of the Three Ugly Sisters was progressive from one end of the site to the other. As the space was cleared, construction of the new buildings followed the same path across the site. Named blocks A, B and C for simplicity, they were built in this order in staggered phases.

The m&e installation was intrinsically linked with the structure, so SES’ early involvement aided co-ordination. At lower ground level the hv ringmain runs underneath the base slab of all three blocks. “When they were forming the slab we had to have ducts installed to take those cables. Then we have an open hv ring underneath the slab, which is very well protected,” said Edwards. Lightning protection and underground drainage for the public health pipework also had to be built-in at this stage.

Inside the building, cast-in conduit has been used in the building columns for distribution to sockets. “Just before the pour of the column we installed the conduits,” explained Edwards.

SES had separate workforce teams for each block, overseen by area foremen who reported to overall mechanical and electrical construction managers. Including subcontractors the firm employed 250 operatives on site at peak.

Plant is located on all three roofs and in basement areas. Each building is basically standalone electrically and has its own dual-packaged substation. These are served by two independent parallel supplies from the hv ring. “The supply had to be 100% back-up,” said Edwards. “We’ve got the two incomers then 100% backup from the generators on block C roof.”

There are two cores in each block, one either side of the central atrium, which contain the m&e risers. The floors are split in half for servicing, with services from each riser core distributing to the half of the block it feeds onto, meeting the other feed in the centre of the floors.

Pre-wired, plug-and-play power track and datacomms is run under raised floors throughout the offices, with powerblocks giving local supplies to desks.

Installation issues

The most complex section of the office areas in terms of m&e installation were the streets around the atriums. Here fixed plasterboard ceilings with decorative holes and lighting were fitted, restricting access and making it necessary to install services before the ceiling. This was impractical for programming.

The life-safety supplies for HOCLAS are fed directly from the generators, which are all located on the roof of block C. To serve the entire development, cabling had to be pulled from this roof, down through the risers, across the floors then over the fourth floor link bridges between the blocks. Before this could happen the bridges had to be in place and the roof almost complete. “The key point was when the roof was available in block C, you could then pull through the building to block A,” explained Edwards.

To add to the problem, the build programme was such that the ceilings were to be installed before floors. This meant that they would have been at different levels of completion in each block when the cabling had to be installed. “It made sense to take that cabling from the ceiling void and put it in the floor void instead, so then you get rid of the programming implications,” reasoned Edwards. Being involved at the design stage meant this could be agreed before starting on site. Having close involvement with the suppliers also paid off in this respect.

Westminster Council have set rulings on the types of cabling that can be used depending on its diameter. Edwards explained: “Any cable sizes lower than [70 mm diameter] you have to use micc, which is rigid, awkward and time-consuming and we were installing those cables from the roof of block C all the way across block C, B and A, up to the roof of A. You’re talking 350-m runs, so in micc it could easily get damaged. It was impractical.”

During the design stage SES preferred supplier Pirelli advised that it was at the approval stage of an alternative solution – the FP600 fire-resistant power cable. At 35 mm diameter it would be easier to handle than micc and, with a flexible steel casing it would have the protection needed for laying in floors. However, before it could be added to plans the Westminster district surveyor had to be satisfied of its quality.

Pirelli began a series of testing in conjunction wth the district surveyor, which led to the product being certified for use. “It was just about timing really, getting the cable when it suited the projet and when it was certified. It was a very tight window,” stressed Edwards. This is the first installation using the new FP600 and the first new building in Westminster to use alternative cabling.

Staff and passers-by alike can’t fail to consider the new buildings a vast improvement on the Three Ugly Sisters.