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Residents in Linwood pull down a damaged chimney before high winds hit. Photo supplied by Jan Jones - Source: Supplied -
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A structural engineer says it is important repair work in Canterbury following Saturday's earthquake is done properly and doesn't literally "paper over the cracks".
Adam Thornton said while the initial assessment of buildings in the CBD is complete, it will take some weeks to check all the damaged houses.
He told TVNZ's Breakfast that an initial review will determine whether a house is safe to occupy, whether it is safe to go back in to retrieve belongings or whether people should stay out altogether. Thornton said a more detailed assessment of repairs and potential costs will take much longer.
The government has hinted at speeding up the consents process and Thornton said he assumes they may be considering altering Schedule One of the Building Act under which repairs or alterations may be undertaken that don't require a building consent. But Thornton said they still have to comply with the Act and it is important repairs are done well.
Residential homes rely on gib or plaster board systems for bracing, and Thornton said what may appear to be superficial damage in a residential building could actually be a lot more. He said if there are cracks in the gib board or rips in the wallpaper it is important they are fully structurally repaired and this might mean the re-nailing and re-plastering of joints.
Thornton said in a commercial building partitions may look the same as in residential structures, but they tend to be non-structural. In houses sheets of gib and plywood are bracing elements and fixed to foundations.
Buildings are not the only concern and engineers will be checking on the stability of the ground. Thornton said there are two categories to look at. He said the first is mainly in rural areas and involves ground disruption where the fault ruptures and "expresses itself at ground level". While this is likely to have caused major damage, Thornton said it is mainly on alluvial material and should setttle down again quite quickly and then remain stable for "about another 10,000 years".
The other form of damage is liquefaction which is more prevalent, Thornton said, and "more difficult to repair". He said if it is a more modern house on a concrete slab, all the concrete is bearing on the ground and if it settles below a certain level, it can be too costly to repair.
The whole process, including a detailed professional assessment, procuring resources, involving insurers and getting costings is likely to take many months.
Thornton said people may have to have more minor repairs and tolerate "a few cracks and broken windows for a while". He said more serious but repairable damage will probably be prioritised because if it is left to the elements it could deteriorate further.
But he stressed it all needs be done in an orderly fashion and checks and balances are critical to ensure repairs are done well.
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