New technique for quake-zone building
Architect William Trengrove is pioneering the use of new residential foundation and building techniques for Christchurch earthquake zones on a central-city block.
He and his wife Alison are taking on one of the first city rebuilds on technical category 3 land, using steel-screw piles down to 15 metres to give stability to the building on Manchester St.
They have also taken on substantial risk. Their project is insured for the contract works but not for natural disaster during the building process.
The couple lost their 1940s art deco-style two-storey home in the February quake but were determined to rebuild on the site as soon as they could.
All going well, the two-bedroom house on top of a 150mm concrete slab, resting on steel beams on top of the metal piles, should be ready for Christmas.
Trengrove has revealed his project on a 500-square-metre section to nearby residents. He talked to the recent annual meeting of the Peterborough Village incorporated society saying the foundation should be able to withstand most heavy quakes with the house able to be re-levelled on top of the piles.
The Peterborough group of residential owners within the area bounded by Colombo, Salisbury, Barbadoes streets and the Avon River have been meeting regularly to see whether they could work closely together to save on redevelopment costs.
The cost of preparing for another big earthquake has not been cheap for Trengrove.
He had paid about $16,000 for a geotechnical study showing a sand base. Then on top of that was another $65,000 for the drilling rig to put in the screw piles, with much of that cost related to getting the rig onsite. Extra pieces of screw pipe could easily be welded on to the initial steel pile to get extra depth.
His architecture firm was also advising clients on another type of housing base, comprising a raft of shingle stones constrained within a confined dug-out foundation area. This was probably less suitable for sandy soils, Trengrove said.
His view on the recently announced city blueprint released by the Christchurch Central Development Unit is positive but cautious in terms of challenges faced by others choosing to rebuild.
"I'm encouraged by the new plan, I think it's exciting, but I'm still realistic that it's going to take a long time."
The settlement process between property owners, insurers and the Government needed to be ironed out as soon as possible, to drive the rebuild process forward. "Even with my own property, I only got settlement from EQC in May. The house was demolished in November."
He negotiated a cash settlement with his insurance company based on the cost of the house built on the land, which also took until May to settle, including an agreement that the money would be used to rebuild on the property.
"Vero have given me contract works insurance, but I've got an exclusion of natural disaster. I've taken the risk on that based on the view that the foundations I've done should be able to handle [earthquakes] . . .
"Plus also the cost and excess on the insurance cover is very high. We're typically finding excesses of $50,000."
When the house was finished he would investigate further insurance cover, he said.
Peterborough Village committee member Di Lucas said the society's aim was to encourage renewal in the area as soon as possible, both in a commercial and residential building sense.
Importantly, there had been a change in some of the zoning within the region from business to mixed use so that both residential and retail operations could sit side by side.
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