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12/05/2017

High aspirations at MacDonald House

Work is drawing to a close on a landmark project in the highly sought after Mayfair area of London, that has required both demolition and earthmoving expertise from specialist contractor McGee.

McGee is currently forging ahead with works to excavate the basement in preparation for a new insitu concrete frame that will support a prestigious new residential development, due for completion in Q4 2019.

This earthmoving element follows a demanding £7.4 million demolition at the site in Grosvenor Square, the heart of Mayfair, one of London’s most exclusive and affluent locations.

Formerly the US Embassy and latterly the Canadian High Commission, MacDonald House, at 1-3 Grosvenor Square, was built in the 1930s.  In 2014 Canada sold the building to prominent Indian developer Lodha UK for conversion into luxury apartments.

Unusually, although MacDonald House is not listed, planning required the retention of the original façade, which is commonplace in the demolition industry. Often, the original elevation is supported with steelwork while the new building is constructed behind.

Uniquely at MacDonald House, the client aspired to create taller ceiling heights, requiring the vertical spacings to be changed. The resulting solution was to dismantle the façade brick by brick and stone by stone, rebuilding it so the windows and other architectural features matched the new spacings.

The taller ceiling heights were not the only reason for dismantling the façade however. It was also incredibly thick, with some of the stones penetrating right through to the inner leaf and causing thermal bridging.

Dismantling and reducing the size of large pieces of masonry enabled the façade to be re-built as a non-loadbearing skin supported by a new concrete frame erected behind it. An additional advantage to this was it freed-up even more living space inside the building.

The building was dismantled from the top down by McGee’s use of a fleet of compact excavators equipped with dipper-mounted “processors” which “munched and crunched” their way through the structure, minimising the amount of breaker use.

This was particularly useful as noise, vibration and dust levels were strictly limited. Typically, local planning authorities take ambient readings and set maximum construction noise levels at a fixed volume – usually 10dB – above this.

This is not particularly onerous in noisy locations such as Oxford Street, but as Grosvenor Square is a quiet address, Westminster City Council set a noise limit of 75dB. In addition, the location was on the site boundary of the Italian Embassy therefore even more care was required to avoid risk of damage to the building and to several artefacts inside. While noise and vibration limits were set very low, permitted structural movement was set at zero.

“From our perspective that means that the odd millimetre movement is OK as long as it’s not trending in any direction,” explained Nick Taylor, McGee’s Head of Demolition. “One millimetre’s fine, but if it moves another millimetre the next day and a millimetre the day after that, that’s not acceptable.”

A bespoke steelwork structure was therefore erected to ensure stability of the Italian Embassy building.

During the demolition, specialist stonework contractor, PAYE, carefully removed and catalogued each individual brick and stone from the façade for storage (on more than 2,000 pallets) at McGee’s depot in Silvertown, east London.

Lodha UK’s Development Manager, Martin Hall said “McGee and PAYE have carried out a complex deconstruction of this historic building and we are excited that work is underway to transform this prestigious London address into a world class development.”

Hall says the concrete frame contract has yet to be awarded as “the methodology is still being developed for the reinstatement of the façade.”

It is likely the stonemason will reassemble the masonry components in a phased sequence as the new building takes shape. Construction is scheduled to begin towards the end of 2017.

The new development, known simply as No. 1 Grosvenor Square, is scheduled for completion by Q4 2019.