Liquefied silt festering beneath Christchurch houses for the past two years could spark serious health concerns this winter.

Silt littered with fungi is piled up against the floorboards of some houses, causing them to rot. In other houses it has crept into the walls, causing mould to grow.

Up to 100 tonnes of silt can be sucked out from beneath a house, removal experts say.

Affected homeowners have complained of bronchiolitus, unshakeable coughs, asthma and other health problems.

Housing New Zealand and the Earthquake Commission are removing silt from beneath the homes of those most vulnerable, but it is not known how many Christchurch properties still require this to be done.

Christchurch medical officer of health Alistair Humphrey said silt pooling beneath homes could cause an array of health problems for Cantabrians.

He said silt held moisture well for long periods and as a consequence houses throughout the city were growing mould.

"All sorts of things can grow in a damp environment like that and cause serious health problems ... such as respiratory illnesses, allergic reactions and breathing difficulties."

The damp also made houses harder to heat, he said.

"Even if the heat is cranked up it doesn't get rid of the cold, and the cold is associated with many different types of illnesses as well."

Humphrey advised Cantabrians to keep their homes ventilated and to remove any signs of mould as soon as possible.

Sewerage pipes around the city broke in the February 2011 earthquake, allowing raw sewage to contaminate the silt during the liquefaction process, and Humphrey urged affected homeowners to talk to their insurer or the EQC.

Housing NZ Canterbury earthquake recovery manager Andrew Booker said some homes had silt leaking through the concrete foundations.

Housing NZ had so far removed silt from five houses and earmarked another 10 to 12 for silt removal.

"If there is any perceived health risk, we need to act quickly, which we have done with the properties identified," he said.

The EQC had removed underfloor liquefaction from about 330 properties so far, general manager of customer services Bruce Emson said.

Some homes had silt against the floorboards and creeping into the walls.

"If the liquefaction is deemed to be causing unhealthy living conditions - typically moisture, mould, mildew inside the dwelling, especially where the inhabitants are vulnerable - then this is given priority," Emson said.

Liquefaction removal company Trans Pacific Industrial Solutions has removed silt from beneath more than 100 Christchurch homes on behalf of Housing NZ and the EQC since the quakes.

Regional manager Trevor Best said a 100-square-metre home could have up to 100 tonnes of silt removed from the floor cavity.

The removal was done by a high-powered vacuum.

The removal crews were "fully encapsulated" with disposable suits and full-face respirators, he said.

Operations supervisor Hamish Sheppard said "it is more common than you think" for homes to have mounds of silt beneath the floorboards.

Canterbury University geologist Mark Quigley observed the movement of silt in his Avonside property after the February 2011 quake.

He said there was "extreme liquefaction" in his neighbourhood, and in some parts of his home the silt had leaked between the floorboards and carpet.

Before his family shifted from their red-zoned home, Quigley said, the house was damp and parts of his garage were beginning to grow mould.

"If we were still in our home now we would have major concerns about the moisture levels and the rotting floorboards," he said.

Pooling silt leaves house damp, family ill

Silt pooling beneath one young Christchurch family's home has left mould growing on the walls and could carry serious health consequences this winter.

Mother-of-two Emily Smith, 31, fears for her children's health.

Her 1-year-old daughter, Holly, has a heart condition that could land her in hospital after any common cold, and silt is festering beneath 3-year-old son Jacob's bedroom.

Smith and her husband's earthquake-hit Woolston home is on technical category 3 land and has been deemed uneconomical to repair by their insurance company.

While they wait for reports on the land, the family are forced to live in a damaged home with silt beneath the floorboards.

The carpet is cold and every morning condensation rolls down the windows. Mould is growing on the walls in the lounge and on the windowsills in Jacob's room.

Smith cleans if off but says it grows back in days.

The family all suffered from head colds "we couldn't shake" that progressed into chest infections last winter.

They installed a heat pump as the fire in the lounge was no longer warming the house and also bought rugs to keep the carpet dry enough for her children to crawl on.

Smith recently went to the doctor for "frustrating" hay fever symptoms such as sneezing, swelling eyes and a runny nose. Her doctor believed her symptoms were caused by a mould or fungi spore in the air.

Jacob had a chesty cough "that won't go away".

Smith is concerned for her daughter's health this year. Holly was diagnosed with patent ductus arteriosus at birth, which means abnormal blood flow occurs between two of the major arteries connected to her heart.

"If she gets sick this winter she won't be able to cope. Her heart will struggle and she will need antibiotics straight away," Smith said.

- © Fairfax NZ News

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