The counter-cyclical buffer is being proposed as a new, slow-acting instrument of monetary policy, which will require a 12 month warning to allow banks to reorder their balance sheets to meet the buffer requirements.
The central bank rejected pleas for earlier warning and for the counter-cyclical buffer to be set no higher than 2.5 per cent of risk-weighted assets.
"A longer notice period runs the risk that the countercyclical buffer is built up too late," the bank said in a summary of its response to submissions on the Basel III rules, which were communicated to banks in May. "In the context of a credit boom it is likely that capital can be raised reasonably easily and even if it could not the bank would simply face restrictions on distributions."
"Dialogue with banks and public signalling of our unease about credit developments" would come ahead of a formal trigger announcement.
On the 2.5 per cent upper limit for the buffer, the RBNZ said "no formal limit on the maximum size of the buffer is appropriate for New Zealand" because of the lack of experience calibrating of the new instrument, and "retaining an open-ended maximum may be useful in conditioning bank incentives against excessive credit growth."
It "acknowledges that further work is needed on the countercyclical buffer framework in relation to financial indicators as well as governance and accountability arrangements for the operation of the buffer."
"However we consider this work can be undertaken in sufficient time to allow the implementation of the countercyclical buffer in 2014."
Further announcements are due in coming weeks on the RBNZ's approach to the controversial issue of "open bank resolution" - a proposal to require depositors and bond-holders to take a financial "hair-cut" in the event of a bank failure.
This story has been corrected from an earlier version, which said the Basel III rules will be implemented in 2014. The correct date is January 2013