ASB will "generally" expect home owners to have a deposit of 20 percent when seeking a mortgage on a house.
ASB said it will still lend to some people with less equity if they have "very strong serviceability".
The bank has tightened its criteria for home loans in a number of ways.
"As a rule of thumb someone with 20 percent equity would generally fit where we would want to be," said Ian Park, the bank's head of retail banking.
He said the bank was being more thorough in assessing living costs borrowers face when it assesses the ability of a mortgage applicant to service the mortgage.
"We are being more realistic with the cost increases that people have had to face in the last 12 months when we look at serviceability of their borrowing," he said.
The bank would also no longer be involved in so called "low doc" loans, which was a tiny part of its business.
These are mortgages where borrowers do not provide independent proof of income but sign a certificate saying what their income is. They are loans made mostly to self-employed people.
"We are saying because we do so few of these, and the way the economy is it is pretty difficult to assess what earnings are, we will now treat it as a normal loan application and get a bit more information on income," he said.
There has been speculation that banks will call on people to have more equity in their properties.
Mr Park said the key thing was for people to keep paying their mortgage and talk to their lender early if they were having problems meeting payments.
He had never heard of a bank requiring more equity in an existing unbroken contract.