New research aims to test earthquake resilience of NZ's many houses built on steep hills

The Building Research Association and Earthquake Commission are addressing a lack of research on the impact of earthquakes on houses built on slopes with a new test.

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It’s a common occurrence in New Zealand, but there’s a lack of research about their risks. Source: 1 NEWS

Nearly 40 per cent of the country’s population are at some risk from landslides, according to research from QuakeCoRE.

A counter-rotating shaker was used on four foundations built with timber framing and concrete piles on a Porirua sloping paddock for the experiment, with dead weight added to the floors of each model to make them more realistic of the weight of a house.

“I can sit here in a controlled environment and I can watch and I can see things moving - in a real earthquake I’d be ducking under the table,” Building Research Association New Zealand project lead Roger Shelton said.

"Two of the foundations were built to replicate the older details of the traditional house foundations found in any hillside suburb in New Zealand and particularly in Wellington.

“Houses built on slopes may have foundations that are significantly taller at one end than the other, or there may be different types of foundation under the same home,” Mr Shelton said.

Houses built on slopes are likely to ‘twist’ in an earthquake due to the uneven foundations, making damage more likely.

The other two models were built to building standards, which still showed signs of damage after being shaken.

“You can see quite a gap between the soil and the concrete and that was caused by the foundation actually rocking like this under the influences of the shaker - that was a little unexpected from my point of view,” Mr Shelton told 1 NEWS about the newer foundation design’s performance in the experiment.

The researchers will test techniques on the foundation models that may reduce damage to an existing house, such as changing the foundation attachments and materials.

The results will be provided to MBIE, who update the Building Code, the building industry and councils that request the information.

“We don’t want to make radical changes to the houses because the home owner has got limited funds to spend,” Mr Shelton said.

It’s hoped the guidance will be particularly useful to homeowners in places like Wellington, which has thousands of homes at risk of a landslide, according to QuakeCoRE.

The Earthquake Commission’s head of resilience strategy and research Jo Horrocks said the majority of the building code is based on flat land.

“We would like to see the code changed in the future if the research supports it, we'd like to see maybe a standard for sloping land and flat land building types,” she said.

“We prefer that people don't build on really steep slopes that cannot support the weight of the houses, we have ways of engineering to make sure houses are safe, but we'd always like to see them built to a higher standard.”

Mr Shelton said the project was created, with $120,000 in funding from the Earthquake Commission, following observations of what happened to houses on hills in the Christchurch earthquakes.

“We saw that the same level of shaking caused more damage to homes in Port Hills areas like Cashmere and Redcliffs than it did to homes on the flat,” Ms Shelton said in a statement.

The testing results are expected to be available in June.

Ms Shelton said he advises owners of sloped properties to get their house foundations professionally checked every five years.