First class services

After lying derelict since 1995, Edinburgh’s former general post office has been given a new lease of life. Located within the city’s World Heritage New Town, the retention of the building’s Grade A-listed facade was essential. To passers-by on the adjacent Princes Street it will look simply as if the brickwork has been cleaned, but behind the stone facade sits a monument to modern engineering: the interior of the GPO has been removed and new offices constructed in the space.

More than any standard refurbishment, it involved the removal of over 30 000 tonnes of material before construction could begin. Building within an existing facade may be difficult enough, but with the site being encased on two sides by one of the busiest roads in the city and the congested North Bridge, plus the rails into the main train station running past the rear, close co-ordination and forward planning were essential.

A change of post

Waverley Gate is the largest office development in the centre of Edinburgh at present, with 19 500 m2 of lettable area on seven storeys based around a central atrium. The brainchild of developer Castlemore Securities, who acquired the site in June 2001 and commissioned architect Hugh Martin Partnership for the task, it will have some of the largest, flexible floorplates in the capital.

Flexibility is essential as it is a speculative development with no confirmed tenants to date. The design is such that the floor can be subdivided for multiple occupancy. This concept led the layout and enabled the first large-scale use of active chilled beams in a commercial development in Scotland.

“All floors are mirror images of each other with the exception of the top floor, the executive level,” explained Tony Griffin, Haden Young project manager. This simplified the layout for letting, plus reduced the building and installation time: as a fast track project, the build was to be completed in only nine months.

Haden Young was the lead co-ordinator on the m&e services. Its role was to value engineer, assist with the design development and co-ordinate the m&e services; plus install the mechanical services. It won the role by a two-stage competitive tender and was closely involved with the design team at an early stage. The team worked together for around one year prior to reaching site, value engineering and preparing the logistics of the project. “From a value engineering point of view, the way we worked together was the biggest part of the project,” stressed Griffin.

Location and logistics

With virtually no room for site cabins, Balfour Beatty decided to rent office space directly opposite. Haden Young and others joined them for the project duration.

Space around and access into the site was severely constricted. “The only way to get materials on site was via the main roads at restricted hours,” explained Griffin. This meant careful planning. “There was a three-month lead-in to shut the road to put in the chillers,” he added. Traffic lights around the site had to be adjusted to divert the traffic flow while the work was being carried out. Crane work from the south had to wait until repossession of the tracks could be arranged with the railway firm and work completed overnight.

The three tower cranes used for moving of plant and materials into site could only lift from 10 pm to 6 am due to the health and safety risks of lifting in a public area. “This actually helped with the programme,” explained Griffin, “as we began double-shifting.” A smaller number of staff worked the night-shift to co-ordinate and offload materials and move them into position for the next day.

Balfour Beatty was in overall charge of co-ordinating deliveries and crane time. Haden Young submitted a weekly listing of deliveries and offload times were allocated. “All [basement] plant had to be in place within two weeks,” said Griffin. “The whole plant area was built in six to eight weeks.”

Apart from crane time, the biggest logistical problem for Haden Young was the access point for the plant. Items for the basement plantroom had to be dropped through a lightwell separating Waverley Gate and an adjacent council building. An elliptical space with a maximum gap of around 5 m, clearance in some cases was only a few centimetres.

Prefabrication was widely used due to the tight programme, with ductwork a notable exception. “Time and logistics outweighed prefabrication in this instance,” said Griffin. “With the number of deliveries and crane hoist time it was prudent to bring it in as flat-pack and build on site. Complex pieces were preassembled, but kept to a minimum.”

Efficient servicing

The m&e services concept begins with the connection of the two buildings. A perimeter atrium has been created between the facade and the new build which acts as a natural thermal buffer zone and forms the basis of the passive stack ventilation system.

The developer and design team were aiming for an energy efficient and responsive building. Simulations were carried out to optimise the atrium width to maximise the amount of natural light into the offices without compromising the lettable area and to calculate the thermal properties and night cooling possibilities.

The UK Carbon Emissions Calculation Method was used in the services design, reportedly its first large-scale use in Scotland. “The design team pushed for a green building and the use of the CO2 code provisions,” explained Griffin. This code gives the flexibility to balance heating and cooling and include energy conservation. Chris Thompson, senior engineer of consultant Rybka added: “Because of the nature of the building – high IT loads – anything we can do to reduce the cooling load is a good thing.”

Distribution of services is based on a six-zone setting formed around three cores. Each floor is served independently from six electrical and six mechanical risers, each pair of risers feeding the area directly adjacent to them and enabling the subdivision of floor space.

To maintain the focus on flexibility of use and energy efficiency, office cooling is provided by active chilled beams. This choice was design-team led and its viability confirmed at the value engineering stage. “It was thought to be cost prohibitive at first,” explained Griffin, “but we found that we could put active chilled beams in if we used standard products. If we’d put in a multi-service beam it would have cost four to five times more.” Beams were installed flush to the ceiling on 3 m centres. This allows for installation of office partitions without the need to relocate services. The beams were installed and tested before Haden Young moved out of the area: “There was no first and second fix. Within days of pouring floors, Haden Young was in and putting in chilled beams,” said Griffin.

Waverley Gate was ready for occupation in January 2005.