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Historic west London riverside chalet raised as protection from flooding

A historic London riverside landmark was successfully raised 1.5m above its original level in a £1.4M operation over the weekend.

On its new foundations Hampton Court’s Swiss Chalet in south west London will be clear of the Thames floods that have damaged its softwood timber structure.

Last Friday specialist lifting contractor Mammoet used eight climbing jacks to raise the 80t building 2m, allowing contractor MS Services to erect the new steel portal frame substructure below. The building was successfully lowered onto its new elastomeric bearings on Saturday.

“We’ve lifted much heavier weights much higher in the past, but this was a particularly sensitive operation,” said Mammoet site manager Chris Wilson.

“All the windows and tiles were left in place, so we had to be very careful to maintain structural integrity and stability.

“In the event, not a single tile was lost and not a single window pane was cracked.”

Sitting only 10m from the bank of the Thames, the Chalet arrived in Hampton Court from Switzerland in 1883 - in three prefabricated sections. Its original function was as a garden folly cum boathouse, but over the years it has been part of a boatyard, a restaurant and a private house. Local rumours insist it was once a gambling den frequented by the likes of the then Prince of Wales and Charlie Chaplin.

“It actually straddles an old dry dock, which has been acting as the basement,” said structural engineer Fairhurst partner Nick McSpadden.

Timber piles

“The original foundations were timber piles driven down to the gravel, but these were subsequently encased in concrete.

“Unfortunately, over the years the original piles have rotted away inside the concrete. And, particularly since the recent floods, the lower house timbers have decayed badly.”

Supporting the house’s timber structure is an original grillage of iron beams - still in good condition - that once spanned between the timber piles.

Fairhurst decided to keep to the original design as much as possible and designed a new substructure of eight steel portal frames.

Architect RRA Architects director Duncan Gunn said there were three main worries before the lift began. “Obviously we were concerned about stability during the lift, and the effects of disturbance after the lift.

“But we also worried about the moment of lift. Over the years the building had become attached to the ground in a piecemeal fashion. We had to be certain that all these connections had been unmade before the jacks started working.”

Leaving the glazing in place was a tough decision, Gunn added. “We were pretty confident the tiles would stay in place, but the slightest distortion of the window frames would cause the glass to crack or shatter.

“So we covered every window inside and out with a safety film, and it all worked perfectly.”

Mammoet set up four jacking towers around the perimeter of the building to support four 200t capacity jacks, and placed four underneath, supporting 50t capacity units. Controlled by computers, the eight jacks lifted the building in 100mm increments. No overlooked ground connections disturbed the progress of the lift.

Once all the work has finished, including a new basement, the chalet will revert to its previous status as a private house, albeit one that will be significantly more habitable thanks to the new elastomeric bearing layer. “There’s a lot of traffic vibration from the adjacent road,” McSpadden said.

“The bearings should minimise the intrusion into the building’s fabric.”

Gunn added: “This may not be the most spectacular Swiss chalet in the world - its importance is as a local landmark. In the context of Hampton Court this is a special building.”

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