Landlords concerned mandatory moisture barriers may damage houses

Property investors are upset at what they say is a potentially dangerous aspect of the new Healthy Homes standards.

Rental properties are required to have underfloor insulation and ground moisture barriers in most cases.

But Paul Beaumont, a former repiler, said moisture barriers stopped water going where it was meant to and could cause piles to sink.

"I used to crawl under a house to put the piles in and the ground was dry and dusty like it should be. Then people put underfloor insulation and polythene in there and six months later they say 'why is the floor starting to drop'?"

He said investigation would then reveal water pooling on the moisture barrier, "pulling everything down with it" because air was not flowing as it should.

Investor Graeme Fowler said it seemed that putting down moisture barriers could create more problems than it would solve.

"In winter, many houses are damp underneath with water being fairly close to the ground surface. Over summer, this generally dries out unless there is very low airflow under the house. Having a moisture barrier on top of the ground keeps the moisture in the ground, rather than bringing it to the surface and evaporating back into the sky," he said.

"Over time this dampness in some cases will cause piles to sink further into the ground. Not in all properties and most likely not in all locations around New Zealand, as it would depend on the ground and also the climate. Also, from the insulation experts I've talked to, they say if a property is fully insulated to the current specifications, the moisture barrier will be of no further advantage at all.

"In our own 1960s home, which has full insulation and good heating, there is no way I'm going to risk putting in a ground moisture barrier. It would be a complete waste of money and also potentially harmful to the piles that the house sits on."

Claire Leadbetter, manager for tenures and housing quality at the Ministry of Housing and Urban Development said it had worked closely with building and industry experts to develop the standard.

"Subfloor moisture is potentially the largest source of moisture in the home depending on the occupants habits. BRANZ research shows us that this could be up to 40 litres each day under a 100 square metre house, even if the soil appears dry.

"BRANZ research has also found ground moisture barriers to be the most effective option at addressing subfloor moisture and more effective than subfloor vents.

"We have talked with building experts about the issue of piles sinking and they are not aware that this is an issue associated with installing a ground moisture barrier."

In a statement, BRANZ said it had no concerns about the barriers causing piles to sink.

"BRANZ has not seen evidence that shows moisture accumulation in the soil directly under the barrier penetrates deep enough to cause the foundations to subside.

"If the ground is wet enough to affect foundations, it is probable there is a drainage problem that evaporation alone is unlikely to control."

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