The Reserve Bank of New Zealand has signalled it will release a discussion document by late March on new macro-prudential tools that could include increased risk weightings for mortgages or limits on loan-to-valuation ratios.Public debate over surging house prices has refocused political attention in recent months about what the government and the Reserve Bank could do to cool house price inflation in New Zealand, which was almost 10 per cent in 2012.RBNZ deputy governor Grant Spencer said in a commentary published in the Dominion Post and the New Zealand Herald that the bank is developing a framework for the use of such macro-prudential tools in consultation with the Treasury and the Finance Minister.The comments reinforced those made in the Reserve Bank's Financial Stability Report in November, where it said it was working on a memorandum of understanding with the Minister of Finance on how and when the tools should be used.The Reserve Bank said in November it was looking at four tools, including: A counter-cyclical capital buffer, whereby banks would be required to put aside extra capital when credit growth was too strong. A higher core funding ratio, whereby banks would have to fund more of their loans with more stable funding such as bond issues and term deposits, rather than short term wholesale funding when credit growth was too strong. Higher risk weightings for certain sectors, such as home loans or rural loans at times when credit growth was too strong in those sectors. Limits on loan-to-valuation ratios for mortgages when housing lending was too fast.It also said then that current credit growth did not justify using such tools, but credit growth has heated up again since early November. Finance Minister Bill English confirmed on Tuesday in Parliament that the RBNZ was working on the tools, but said there was no rush."They need to work through it properly," English told Banking Day before entering Parliament for the opening statements of the year.The Reserve Bank is expected to hold interest rates on Thursday morning when it releases its next monetary policy decision. New Governor Graeme Wheeler is expected to address the wider economic outlook and rising house prices in a broader speech to begin the year around midday on Friday.