House mould risk worsened by recent flooding, BRANZ says

The Building Research Association of New Zealand, or BRANZ, is urging homeowners affected by the recent flooding to be vigilant about mould growth.

Residents in many parts of the North Island are in the process of trying to put their homes back together after being hit by torrential rain and flooding in recent weeks.

Wellington Mayor Andrew Little has said costs of damage from Wellington's recent storm could be in the hundreds of millions of dollars.

BRANZ resilience research project co-leader Catherine Nicholson told Nine to Noon that New Zealand homes were already known to be vulnerable to mould.

"Some of our past and ongoing research here at BRANZ has shown that around about 50 percent of homes actually already have visible mould.

"That's largely due to single glazing, limited heating and ventilation. And then when we add flooding in on top of that, we really dramatically increase the risk of mould growing."

That could start within just a few days if a home is not dried out thoroughly after a flood, she said.

"The first thing that people want to get onto is getting that drying started using heaters, fans, dehumidifiers."

People should also do their best to check potential hidden entry points in their houses, Nicholson said.

"So, having a look around your windows and doors and also in your ceiling and roof space, if it's safe to get up there."

Owners particularly needed to ensure buildings were thoroughly dry before starting repairs such as replacing plaster board, she said.

It was also important to consider flood risks during renovations, through raising up appliances, cabinetry, and power points, Nicholson said.

The way properties were landscaped also could have a large impact on their susceptibility to flooding.

"Those hard impermeable surfaces, this is where we see a lot of the problems.

"If you're able to replace some of those with grass or gardens or even permeable pavers or gravel, if you don't quite want to get to the flower bed stage, [that] can be really, really helpful."

The goal was not to stop the water, but rather to help guide it away from the home and help it absorb into the ground, she said.

Residents also needed to talk to their neighbours who may have unintentionally landscaped their home in a way that makes flooding worse, Nicholson said.

"I think last week's events really have highlighted that community level solutions are needed to this wider problem."

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