42 — Build 143 — August/September 2014

InnovationFEATURESECTION

UNINHABITABLE HOUSES, land that can’t be used, mountains of demolition waste and the urgent need to fast track home building are all problems Christchurch has to deal with. So what creative thinking is solving the overlapping problems the city faces?

Lift ‘em highMany houses in TC1, TC2 and even TC3 have only superficial damage to the superstructure

Versatile, modular system‘The system we have developed is a purpose-built high-lifting jacking system that is designed to speed up and reduce the costs of repairing building foundations,’ says Brent Smith, General Manager, Residential Lifting, Rebuild and Relocation at Smith Cranes and Construction.

‘First, the building has to be braced inter-nally to hold everything rigid. We then insert

Fresh thinkingThe Christchurch rebuild is one of the biggest challenges facing the

building industry, yet the devastation has inspired many outside-the-square solutions. Here, we look at a few of them.

BY NICK HELM, FREELANCE WRITER, TENPOINT COMMUNICATIONS

The high-lifting jacking system saves homes from demolition by providing access to replace damaged foundations.

but are often destined for demolition because the foundations are a write-off.

It’s not that the foundations can’t be replaced, it’s just not feasible to put the house to one side while the old foundation comes out and the new one goes in.

However, a novel house-jacking system developed by Smith Cranes and Construction means many of these otherwise repairable homes can avoid ending up in landfill.

Build 143 — August/September 2014 — 43

the lifting trusses, either through the walls or underneath the floor. The trusses are then securely braced and tied to the structure of the house,’ he says.

While masonry veneer cladding must be removed before the lift begins, heavy roof claddings can be accommodated by increasing the number of support trusses.

‘Every house is different, and the system is fully modular, so we can put in more jacks and trusses for heavier houses and use fewer, more widely spaced jacks for light houses, or we can lengthen the trusses for wider houses or shorten them up for narrower houses. It all depends on the outline of the building,’ he says.

It takes approximately 2 days to prepare an average house and usually another week to completely demolish and remove the old foundation.Space to work‘There is 3 m of unimpeded space below a jacked house, which enables heavy machinery access to demolish the old foun-dations and rebuild new ones,’ says Brent. Compare that with conventional jacking systems that can only lift a house by about a metre and don’t provide much access below the supported structure.

the foundation we usually excavate the top 300 mm or so and pack it back up with 200 mm of compacted hard fill,’ says Jon Hambling, National Technical Manager at Firth.Grid of jack points‘The foundation itself is a twin-slab arrange-ment with a specially designed fast-curing concrete brew, which incorporates thou-sands of steel filaments to add reinforcing. The boxing is set up once and used for both slabs. The first base slab is poured, and the next day, they’re back setting up the top slab, so there is really only one or two additional days of construction. It is very quick,’ he says.

‘Most of the base foundation looks similar to standard RibRaft®, but where the jack points are located, there are 400 mm wide internal beams, which transfer the high point-loads from the jacks across the slab. It also provides the foundation with additional stiffness, so if the ground does settle or liquefy, it can resist a great deal of movement around or directly underneath the slab.’

At any time in the future, the jacks can be accessed by lifting the floor covering and inserting bolts into the jack points.

Innovation FEATURESECTION

RibRaft TC3® foundations can be relevelled if the ground moves.

The system was originally intended for use with concrete slab foundations, but Brent says it has become popular with owners of older wooden houses as well.

Is provides plenty of room to get in under the house to construct an appropriate foun-dation for the ground conditions. ‘When you think that the rebuild costs for older-style wooden houses are up around $3,000–3,500 per square metre, it makes a lot of sense to use a system like this,’ he says.

Staying level in TC3Concrete specialist Firth has developed an innovative solution to building slab founda-tions in Christchurch’s TC3 zones where minor to moderate land damage is possible in a major earthquake.

A fundamental objective for new building in TC3 is the ability to relevel the foundation and bring the building back into a level plane after a future earthquake event. The new foundation, RibRaft TC3®, is based on a standard RibRaft® flooring system, but it sits on top of the ground rather than in it and uses a series of threaded levelling jacks cast into the slab.

‘Typically, the top layer of ground mate-rial is very weak in TC3, so before we place

44 — Build 143 — August/September 2014

The jacks are located in a grid arrangement on approximately 4 m centres, so the larger the house, the more jack points the founda-tion requires.Filling in the gaps‘When we tested it with a full-size house foundation, which was loaded with about 40 tonnes and slumped by about 120 mm, a couple of carpenters and I managed to have it back in a level plane within about 2.5 hours using common trade tools,’ says Jon.

When the foundation is lifted into a level plane and the jacks are holding it in place, a cavity typically 20–150 mm deep forms between the two slabs layers.

‘At that stage, you temporarily shore up the perimeter and pump in a high-flow low-viscosity grout. Once the grout has set and come up to strength, you wind the bolts off, take the forms away, put your flooring back down and the building is ready to reoccupy. The whole process usually takes no more than 4–5 days.’ For more See the RibRaft TC3® foundation at

cera.govt.nz/video/ribraft-tc3-foundation-

solution.

Recycling from the red zoneDespite advances in foundation design and repair, the only possible outcome for houses in Christchurch’s red zone is demolition, despite many still being in good condition above the foundations.

Rather than lose them to landfill, Mac Developments is one of the operators who deconstructs, relocates and reconstructs these houses on new sites around the country.Deconstructing with care‘The process we use to deconstruct a home is pretty much a reversal of the process that you would normally see during a build,’ says Daryl Hodder, founder of Mac Developments. ‘The kitchen and bathrooms come out first, then the wall linings come off, the insulation comes out, followed by the frames and the trusses coming down.’

Every element of the deconstructed building is carefully recorded, packed and

InnovationFEATURESECTION

Modern houses in the red zone are being deconstructed, packed up and rebuilt elsewhere.

Deconstructed houses are packed before being shipped to their new site.

Build 143 — August/September 2014 — 45

Innovation FEATURESECTION

stacked into shipping containers before being transported to its new site, ready for reconstruction. Daryl’s deconstruction team also carries out minor earthquake repairs before they pack the houses, although the type and severity of the damage limits what they’re able to take on.

‘We can’t really repair joinery or things like that, but if it’s cracked timber in the walls or subfloor or another framing problem and we can repair it, then we’ll go ahead and make repairs before we pack it up,’ he says. ‘But if something has been damaged beyond repair, then it doesn’t get packed with the rest of the house.’Need to meet Building Code and suit siteIn order to be considered for the decon-struction process, a house must be built in 2004 or later – houses built from 2005 on are preferred. This ensures they comply with the requirements of the current Building Code and reduces issues with approvals and inspection when the home is reconstructed.

Like any building process, it requires a lot of due diligence. The property has to fit the new site, and homeowners should be aware of any covenants and subdivision require-ments that are in place. The seismic, wind and snow loading requirements for the new location also need to be checked – additional fixings and bracing may be needed.

The building also has to have foundations to suit the ground conditions at the new site, and all the existing materials have to be certi-fied through the building consent process.

Daryl says a deconstructed home isn’t for everybody, but it’s a good, cheap and reli-able way of building. If not deconstructed, the homes would end up in landfill, and he says the idea of recycling a home appeals to many people. For more See the deconstruction process in

action at cera.govt.nz/video/flat-packing-homes.

Production line homesAs pressure mounts for the industry to deliver, two builders hope to increase

insulation and electrical wiring is installed. Other sections take care of exterior clad-dings, plumbing fittings, installing windows and doors, service penetrations and so on.

The machinery performs most operations to a precision of 0.1 mm. However, there are some limitations.

‘A mono-pitch roof can be connected in the same way as the walls, but if the home-owner wants a traditional truss roof, it has to be finished manually,’ he says. ‘Most sheet, weatherboard and metal profile wall clad-dings can also be completed at the factory, but if the homeowner wants masonry veneer, the panel leaves the factory with building paper and cavity battens so it’s ready to start laying the bricks.’Connect, plaster and finish on siteOnce the panels are on site, it’s a matter of connecting them together, plastering the internal joints and preparing for final finishing.

‘Almost everything happens in the factory, but to a larger scale, much more efficiently and to a higher precision than in the tradi-tional building process,’ he says.

‘ W h e n we b e g i n p ro d u c t i o n o n 15 December, this facility will be able to build enough panels for two homes per day, and we anticipate it will at least halve traditional build times.’

Automated production lines produce panel sections precisely and cost effectively.

productivity by reinventing the build process itself.

For the many cases where building a new home is the only option, homeowners want a high-quality, cost-effective and timely build. Spanbild and Mike Greer Homes have joined forces to invest in a large Christchurch manufacturing facility that will produce fully pre-constructed wall, floor and roof panels.Panels made on automated line‘If you imagine a house as an envelope with six walls, the new factory will make all of those walls, complete with framing, insu-lation, external cladding, internal lining, electrical wiring, plumbing services and fittings,’ says Tim Blake, General Manager Business Development at Spanbild. ‘Those panellised sections are then transported to the site and rapidly assembled into the finished house. It is quite different to what many people think of as modular or prefab building.’

The facility is based around a series of automated production lines. One section cuts long runs of timber into the right lengths and passes it to another section that sets it out and automatically nail-guns it into a frame. Another table flips the frame over and attaches a plasterboard lining, cuts precise openings for windows and doors, before pushing it down to another table where the