A Grade II-listed landmark office job has proved to be as much new-build as refurb and has also benefited environmentally from a 12-month delay.
Project: Africa House Redevelopment
Client: Freshwater Group
Contract value: £25m
Main contractor: Bam Construct
Architect: JM Architects
Project manager: Parsons Brinckerhoff
Structural engineer: Taylor Whalley Spyra
Consultant: Watkins Payne Partnership
Completion date: August 2013
London’s unquenchable thirst for high-quality office space has proven to be one of the few sources of business amid the hostile economic downturn.
Prime office space throughout the capital is in high demand and fortunately for contractors there are still enough developers willing to plough their money into commercial property ventures.
But potential lessees have become more particular about their requirements and developers are demanding more from contractors in a move to meet those expectations.
In Holborn, central London, Bam Construction is focused on one such scheme: the redevelopment extension and transformation of a Grade II-listed block from dated corporate headquarters to contemporary space perfect for the slick City solicitors.
More than a refurbishment
Far from being a standard refurbishment, such are the schemes’ demands that almost 50 per cent of the overall project cost is wrapped up in the new construction side of the project rather than the refurbishment.
“In reality it is more a remodelling project than refurbishment,” says Bam Construction senior site manager Justin Brown. “There has been such a massive amount of structural change throughout the scheme that calling it a refurbishment project doesn’t do it justice.”
“There has been such a massive amount of structural change throughout the scheme that calling it a refurbishment project doesn’t do it justice”
Justin Brown, Bam Construction
Completed shortly after the First World War, Africa House features an ornate Portland Stone façade, which has been retained. But it is to the rear of the property and its roof that the real structural changes are being made.
Two extra levels are being constructed above the existing roofline, with the new mansard roof providing extra office space and a plant level. A new sloping glazed curtain wall is being introduced at the rear of the building, extending the footplate of some of the floors and allowing light to flood in.
The existing large central lightwell is being replaced with a new core featuring four lifts – two of which will be scenic – a fire fighting and goods lift, a new staircase, glazed atrium and kitchen and toilet facilities. An existing staircase is also being retained.
Relaxed bookmaker and anxious pub tenants
Although the bulk of the building is empty, there are two existing tenants that the Bam team have had to work around for the duration of the project.
“Both the Ladbrokes and JD Wetherspoon businesses on the ground floor have stayed open throughout the project,” Mr Brown says. “Working around them has made programming a little more difficult, but we have worked closely to make sure they have been affected as little as possible.
“Ladbrokes were reasonably relaxed about what work we were carrying out as long as we kept the satellite and electronic link for their systems in place, while JD Wetherspoon were anxious we avoided the 10am to 2pm slot, which is a busy time for them.”
Strict noise limits formalised
But with so many law firms based in the area as well, planning authority Camden Borough Council advised the site team to take the extra step of applying for a Section 61 agreement.
This formally sets out the timing and level of noise during the work, stipulating weekly and monthly noise averages that cannot be exceeded without very good reason.
“We managed to work within it throughout,” Mr Brown says. That the site staff were able to do that while carrying out such heavy engineering work is a nod to their skill.
The design called for a new steel frame to be built within the existing light well and connected into the existing concrete clad steel frame once the lightwell walls had been removed.
Extensive shoring employed
This meant a multitude of complex temporary works to support the existing frame as the new section was installed.
Raking shores and flying shores spanning 12 m to 15 m across all floors helped prop the building, while a raft of 350 mm-diameter CFA piles were installed to depths of up to 25 m into the underlying clay.
“Lots of the original steel is in concrete encased beams – it’s how engineers guaranteed their integrity in those days”
Justin Brown, Bam Construction
From these piles the new steel frame has been launched skyward toward the new mansard roof, which will house the eighth floor office space and plant rooms above.
At each level the old concrete-clad steel frame of the existing building is tied into the new steel frame of the core. Each connection was challenging, according to Mr Brown.
“Lots of the original steel is in concrete encased beams – it’s how engineers guaranteed their integrity in those days,” he explains. “But for us it meant that we had to cut the beam through, clean off any concrete and then splice onto the new steel. There were some very intricate connections.”
Massive steel beams
The biggest single steel elements brought into the scheme were 9 m long, 750 mm deep beams, which spanned across the piles in parts of the lower ground floor, but the trusses for the mansard roof where much larger.
At 25 m long and 4 m in depth, the trusses help provide the office space and support for the plant level above the roof. They also support the huge, heavy sections of lead flashing and detailing that really set off the completed structure (see box).
A 350 mm-thick reinforced concrete roof slab helps support the plant, while at other levels standard 150 mm-thick composite steel/concrete slabs have been placed.
Like many city centre projects, just getting such large structural elements onto site in the first place has proven taxing. At some points just 9.5 m separates the building from its neighbours, leaving the single tower crane located in the atrium to inch the steel beams from delivery location and onto fixing points.
“We had to suspend a bus stop and a loading bay outside,” Mr Brown says. “We were on the Olympic Route and so had deliveries on 48-hour notice going in at the back of the site and taking waste out at the front. When we brought in some of the stillages for the glass work it was a tight squeeze.”
The tower crane is now down and the team are focused on putting the final touches to the category A office space before it is handed over in August.
And both Ladbrokes and JD Wetherspoon can look forward to eight floors of potential new clients on their doorstep.
Environmental excellence in Holborn
Meeting exacting environmental standards has always been high on the agenda for the developers at Africa House. From the very beginning it had been determined that the development would reach as high on the BREEAM scale as possible.
When the development was first mooted in 2007, a rating of Very Good was targeted by the client Freshwater Group; it then became an obligation of the section 106 agreement with the planning authority.
But as the downturn took hold, the project was shelved for 12 months until the economic outlook in the capital looked a little brighter.
Although this delay meant a retendering process, it did enable the team to look at the possibility of pushing the project further up the scale to BREEAM Excellent.
“That year gave us a period where we could really identify what it would take to gain an Excellent rating,” explains Parsons Brinckerhoff project director Bob Wright.
“We realised the industry was moving quickly and that the availability and suitability of some products had changed. It made meeting the tougher target more cost-effective.”
Measures such as using recycled aggregate and ecology surveys, coupled with a wood-fired biomass boiler, rainwater harvesting, green roofs and bio diverse planting have all ensured the scheme is on target to meet its BREEAM Excellent objective.
1920s reception roars back to life
The ‘Roaring Twenties’ were little more than a few years old when the great doors to Africa House reception were first opened.
It was a time of optimism and opulence and the imposing entrance hall reflected that mood. With is white marble and art deco detailing, it is no surprise that, along with the façade, it is one part of the building that is protected by its listed status.
But that doesn’t mean there hasn’t been plenty of work to do bringing it back to its former glory.
Years of cigarette and cigar smoke had dulled the light marble and wooden panelling, but a concerted cleaning effort has seen it restored to such an extent that the dark marble detailing around the hall – initially assumed to be black – has in fact been revealed to be blue.
Extra matching marble is being cut into position where restoration requires it, but the layout is being tailored to reflect its new status as a modern, prestigious development and to allow access to the new lift core.