The organisation that supported the Royal Navy through the Second World War is getting a new office that will set a course for its future.
Taunton is an unassuming place: a historic county town in the middle of Somerset that draws little attention compared with the major nearby hubs of Bristol and Exeter.
It’s perhaps surprising then that this land-locked town is home to the Hydrographic Office – the government agency that provides surveys, charts and data to mariners and maritime organisations across the world.
In fact, the UK Hydrographic Office (UKHO) has been resident in Taunton since 1941 when, during the dark days of the Second World War, operations for chart-making were transferred over to a purpose-built factory on its outskirts.
It has been there ever since with additional office accommodation in the late 1960s and 1970s helping expand its influence and workforce.
Now those office and production centres are showing their age and the race to build a modern, attractive, energy-efficient facility has begun.
Bam Construct has taken the £28m contract to build the new office after a two-stage tender process under the Southern Construction framework, which will see project manager Dermot Parkinson and his team deliver the completed office building by December 2018.
“The UKHO is a big deal for Taunton and the new office is a big deal for the UKHO,” he says. “It needs to be right for them. It will be an exemplar office that will reflect [its shift] into the digital age.”
The office development is being delivered on a section of the UKHO campus under two phases. The first has seen the team demolish a range of postwar low-rise buildings and clear service roads and parking spaces to create new landscaping, access and car parks to the development, while the second phase is the construction of the three-storey office block itself.
“The UKHO is a 24/7 operation, so we need to [maintain] unrestricted access for its workforce throughout our work,” Mr Parkinson says. “That has included the 500-space car park. There were some low-rise buildings that were stripped of asbestos and then levelled before the new car park was put in. The office development is sited on top of the original car park.”
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Built in two, three-storey blocks linked by a glazed central atrium, the building features a cast in-situ reinforced concrete frame in the north and south blocks with precast concrete beams spanning the two.
These support the skylights across the flat roof which stretches across the entire building.
“That central atrium is one of the key features of the job,” Mr Parkinson says. “The architect specified the clean-edged industrial concrete finish so we had a choice between fabricating with steel and then encasing with board and painting to get that look – which might have been a little cheaper but would have involved a lot of working at height – or using precast concrete.” He explains that although heavier, it meant there would be limited working at height and little maintenance once installed.
Cladding off the chart
It’s been many years since the UK Hydrographic Office splashed out on new office accommodation and it wants this latest addition to its fleet to be as worthy as any landmarks on the charts it creates.
This is a high-quality building, from the window fittings to the skylights. Nowhere is this level of attention and finish more obvious than in the cladding, both inside and outside the building.
There are two different finishes that dominate: linear timber cladding and a long, thin Dutch-style brown brick.
This dense concrete brick is just 50 mm deep but 600 mm long and is being placed on a 10 mm raked out bed of mortar with a flush perpend joint. Although the longer brick didn’t inhibit the team from specialist contractor Sandford during laying, the bricks were pre-cut offsite for placement around difficult details such as door jambs and reveals.
The team will also install Siberian Larch cladding around the building.
This high-quality material is being used both on the exterior and the interior. Large acoustic baffles run the full length of the building. Hung from the precast concrete beams, they are cleverly detailed to look as if they continue through the glazed curtain walling.
“There were some initial concerns about the brick cladding, but by pre-cutting them we were able to work around the awkward details,” Mr Parkinson says. “The Siberian Larch cladding is another high-quality finish on what is a high-quality building.”
Initially the project team had planned to use plant and powered access during cladding installation, but after some consideration elected to install a standard scaffolding cage around the structure. Given the type and scale of cladding work that was to be carried out and the amount of space that was available on site, it was felt that scaffolding offered a better solution. That availability of space also offered the team the flexibility to work with mobile cranes rather than towers.
“The initial aspiration was that we would work off plant, but in the end that didn’t work out,” Mr Parkinson explains. “A MEWP can only handle two people working from it at any time. We felt scaffolding would be easier.
“We didn’t want the bricklayers having to load and move plant all the time. They wanted to get on with it and we had to provide access for the timber cladding installers. We had room on site and the budget for the scaffolding. It made sense.”
There are 10 beams in total with lengths of 15-28 m and weighing in at 15-30 tonnes. They are in a truncated ‘V’ cross-section and sit in precast notched saddles, which are fixed to the cast in situ reinforced concrete that comprises the rest of the structural frame.
Once again the project team faced a decision between precast concrete, steel and cast in-situ concrete for the framing material.
Steel was quickly dismissed, but weighing up between precast and cast in situ took longer. In the end the team decided that the ease and speed of construction of in situ concrete would win out for the frame, which has seen 8,500 cu m of material poured.
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“We looked at precast for the frame but really the project suited a cast in situ solution,” Mr Parkinson says. “The final building will feature an open ceiling soffit and exposed concrete face throughout.
“The final finish needs to be as close to perfect as possible.
Our concrete frame subcontractor has done that.”
Despite the fact the frame is a relative heavyweight, there is no piled foundation solution. The building sits on a 350-400 mm-deep reinforced concrete slab, which has seen the team dig out to 4 m to find well-consolidated mudstone on which to cast the slab.
“We had hoped to balance the cut and fill, but we did have to take some away – not too much, but we had to go further than we had planned to find suitable strata,” Mr Parkinson explains.
The completed building will be BREEAM Excellent and includes some interesting features to support that achievement.
“The UKHO is a 24/7 operation, so we need to [maintain] unrestricted access for its workforce throughout our work”
Dermot Parkinson, Bam Construct
Along with the large sections of glazed curtain walling at each end of the building offering significant solar gain and underfloor heating across the inner access bridges, it is naturally ventilated with double-louvered energy-efficient windows.
These windows feature two distinct sections: a manually operated louvre that offers workers a degree of control over their local environment, and a mechanically operated section that is controlled through the building’s central management system. A photovoltaic array on the roof helps offset some of the its electrical consumption.
Up on the building’s flat roof, subcontractors have been fitting a hot-melt asphalt roofing system. It offers the flexibility of standard hot-melt techniques but with the longevity offered by modern systems.
“It is robust and self-healing,” Mr Parkinson says. “The modern systems have a fibre layer that helps stop the asphalt cracking as it ages. It is taking a tried and tested method, refining it and applying it to modern day construction. The system suits the climate here.”
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There are a little over six months to go before the completed building is handed over to the client and it makes the move from its existing ageing, inefficient buildings.
It will be a marked change for those cartographers and hydrographic surveyors as they continue to provide essential charts and information for mariners around the globe.
Like all construction work for government departments, the new UKHO is being delivered at BIM Level 2.
The team has benefited from the fully integrated model that has been developed across the project.
Without it the team might have struggled with the complicated detailing and pre-cutting of the bricks around doors and windows as well as the accurate installation of the prefabricated acoustic baffles that run the length of the building.
These baffles are manufactured in 1-1.5 m sections offsite with Siberian Larch cladding preinstalled and then hung in position.
The preinstallation and design has been particularly useful for the project team, according to Mr Parkinson, with the mechanical and electrical design another area that has benefited from the fully integrated digital model.
“All of our subcontractors have completely bought into BIM. They understand the benefits it brings, particularly the mechanical and electrical teams,” he says.