Asbestos in the ceilings of more than 4000 earthquake-damaged homes will be left encased behind plasterboard - a situation Canterbury's leading medical adviser says is a health "landmine".
The Earthquake Commission (EQC) estimates 43,000 Christchurch homes due for quake repairs could contain asbestos.
In about 10 per cent of cases, asbestos in ceilings has been "encased" behind plasterboard instead of being removed.
Homeowners will be told if this is done in their house, but there are concerns encasement may encourage them to hide the information.
Canterbury District Health Board medical officer of health Alistair Humphrey says the practice is a serious health risk.
"I personally feel encasement is not a good thing to do under any circumstances," he said.
"It disguises the fact that it is there.
"We have an opportunity to make sure houses are safe. They should just take it all out.
"It is a landmine sitting there which we won't know about."
'Very unfortunate legacy'
Asbestos was once used in construction and can be dangerous if it is disturbed.
Health experts say it is most harmful if a person is exposed to high levels of the material for a long period.
Prolonged, chronic exposure can cause various lung diseases, including cancer, but can take decades to develop.
Humphrey said the encasement policy would leave "a very unfortunate legacy" for Christchurch, and he has told EQC of his concerns.
"In the future, no-one will know asbestos is there. It is covered over. At the moment, you can look and see straight away it is there," he said.
"Ten years down the track, someone could decide to put downlights in a room. They drill into [the asbestos] and put themselves at risk.
"You could have a little baby crawling around on a carpet for six months with asbestos in it. [Adverse health effects] would emerge only when they were in their 20s, and they will not know the source. It is a very unfortunate legacy."
EQC home repair programme manager Reid Stiven defended the policy.
Asbestos ceilings were encased only when they were not damaged or deteriorating, Stiven said, and homeowners were informed if asbestos was found in a property and if it would be encased.
"EQC always tests for the presence of asbestos where it is suspected," he said.
Humphrey said landlords would be reluctant to put asbestos on the official information record for their home, known as a land information memorandum (LIM).
"If you have a severely damaged house that has asbestos in the ceiling and they encase that, do you think landlords will put that on the LIM? If they do, it devalues their house. Nobody will put asbestos on the LIM," he said.
Stiven said the encasement policy followed health guidelines.
"Enclosing is a reliable method for ensuring asbestos is safely contained," he said.
"We are following the relevant national guidelines and the recommended practice of Canterbury Public Health. Asbestos is only a health risk where it is damaged or deteriorating, and in those cases it is removed.
"All of our EQC field staff and Fletcher EQR supervisors have been given training in the correct identification of asbestos.
"If they suspect asbestos is present, then a sample is taken and sent to testing. This is completed by an independent specialist."
The working group that developed the EQC asbestos policy was chaired by an independent health and safety consultant, he said.