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Behind many of London’s historic facades lurk brand new buildings offering modern high-quality accommodation in prime locations – at prices to match. And delivering these premium projects often demands a great deal of engineering ingenuity.
Contractor O’Keefe has recently completed the very delicate enabling works for the £9.5m redevelopment of an elegant Edwardian building in Mayfair.
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The firm has demolished nearly the entire structure at 13-14 Hanover Street, leaving only the original façade supported temporarily on its bespoke structural steel frame.
Behind this façade, O’Keefe has excavated a cavernous two-storey basement and has just finished the process of building the in-situ concrete retaining walls and basement slabs.
The project, for developer Frank Capital and designed by architect Blair Associates, will ultimately deliver new Class A1 commercial premises comprising five floors of office space with retail space on the ground floor. The site also includes 6-7 Pollen Street, a narrow thoroughfare running perpendicular to Hanover Street.
Besides the technical demands of retaining the building’s original façade, O’Keefe has had the additional challenge of demolishing a building with party walls on three sides.
“It’s a very delicate job,” comments O’Keefe’s project manager, Kevin Hartigan. “All the neighbouring buildings are fully occupied and one of them is a Michelin-starred restaurant.”
The works have had to be very carefully planned and all noisy operations scheduled so as not to disturb the neighbours. “We’re talking to them all the time,” explains Hartigan. “We let them know when we need to plan noisy work, and they let us know when they need quiet. We work around them,” he adds.
Noise, vibration and dust all need to be minimised. “We have site monitoring equipment set up to take readings all the time. We have a surveyor come in every week and we get a weekly report,” says Hartigan.
“I also send a weekly report off to our client. Plus we have a monthly meeting with the local authority environmental people,” he adds.
Traffic is another top priority for the site team, says Hartigan: “Good traffic management is essential because this is a very busy location. We’re on several bus routes – all the buses come down here!”
Due to the extra basement level, O’Keefe has had to underpin to a depth of up to 7m along all of the party walls. The retaining wall along Pollen Street was originally specified as a steel sheet-piled structure, but O’Keefe modified the design to use contiguous bored concrete piles.
Hartigan explains: “The original design would have interfered with a mains electric supply running along Pollen Street. The cables would have had to be lifted and moved temporarily to the other side of the street.
“Our solution was to install contiguous piles in front of the existing retaining wall, which got us round the problem.”
Logistically, one of the biggest challenges has been to coordinate the works so that O’Keefe could simultaneously carry out underpinning and piling works while demolishing the upper storeys of the old building.
“We also designed and installed all the temporary supporting steelwork for the façade, which is very complex,” says Hartigan. The steel was designed in-house and fabricated by Mareth Fabrications, based in Slough.
By mid-February, O’Keefe had poured the lower basement slab and was beginning to install the reinforced concrete basement walls. “Next, we’ll be fixing the formwork for the B1 basement slab and then continue up to ground floor level,” says Hartigan.
After that, construction of the new building, on top of the basement and behind the original façade, can begin. That will be carried out by another contractor, yet to be appointed. However, O’Keefe continues to maintain an interest in the project and has already priced the concreting for this next phase.
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