Kew Gardens

Statement

Client:  Kew Gardens
Main Contractor:  ISG
Type of Works:  Refurbishment
Value:  £41M

‘Indoor landscaping’ might sound like a classic oxymoron, but that’s what O’Keefe was required to do as part of the £41m refurbishment of the world-famous Temperate House at Kew Gardens, west London.

The Grade 1-listed cast-iron framed structure is the World’s largest surviving Victorian glasshouse – big enough, apparently, to contain three Boeing 747s

Scope of works

O’Keefe was employed by main contractor ISG to carry out the internal paving, drainage, groundworks and landscaping, as well as completing the external drainage and laying tarmac roads and paths.

The company started on its £4m subcontract works in October 2014, completing the work at the end of April 2018.

Considerable care needs to be taken when working on a Grade 1-listed building – especially one built primarily of glass and brittle cast-iron. The structure itself cannot be altered in any way without permission of the authorities; and that permission is rarely granted except in the most extreme circumstances.

Unable to create an entrance through the side of the building to provide access for its plant and equipment, O’Keefe had to bring everything in and out via the existing main door – only a couple of metres wide.

“The door access was not wide enough to use big plant like excavators and cranes, but the main service trenches [which O’Keefe was required to excavate] were large. The biggest was 3m deep, 3m wide and 100m long,” explains O’Keefe’s project manager Raj Thiyakarajah.

This, and all the other earthmoving inside the building, was carried out by one 8-tonne midi-excavator and two 3-tonne site dumpers. All the concrete was delivered by the dumpers and the steel reinforcement was brought in manually in lengths to ensure manual handling H&S requirements were adhered to.

O’Keefe’s task involved the installation of specially-designed precast concrete shelves in the glasshouse’s two octagons; one at the northern end of the building, the other in the southern end. These were 100mm thick concrete slabs with special shapes and were installed after the paving works were finished.

The lack of heavy machinery inside the building meant that the concrete shelves, weighing up to 350kg each, had to be manhandled carefully manoeuvred through the narrow door and then, using floor-lifters and trollies, taken one by one to the octagons and lifted manually onto their frames. O’Keefe spent three weeks installing all 100 slabs.

Vehicle movements also proved to be a challenge. O’Keefe moved 500 lorry-loads of muck on this project but as the Temperate House is 500m away from the main road, all vehicles had to be escorted from the garden boundary to the site boundary by a banksman, one lorry at a time. Access was via a temporary roadway and Euromats.

O’Keefe was moving up to 10 lorry-loads a day, but progress was programmed to be slow, taking up to 45 – 60 minutes for one load.

Besides these challenges, there were unforeseen complications. It was discovered that the building originally had a basement which had been filled in, but there were no longer any records of this. This meant as O’Keefe were excavating they were finding old walls and floors, which even the designer was unaware of.

All elements of a listed building are protected by default. This meant that, though they were buried in the ground, these old basement structures had to be preserved just as carefully as the magnificent iron-and-steel superstructure.

Despite these unforeseen obstacles, O’Keefe completed its work before May, when the meticulously restored Temperate House – complete with its 10,000 rare plants – was re-opened to the public.

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