Federal banking regulators have released the final version of new, tougher rules for residential mortgage underwriting practices.

The Office of the Superintendent of Financial Institutions (OSFI) published the final version of its updated underwriting rules Thursday. A draft of the new guideline was first published for comment back in March, and a notice detailing some of OSFI’s policy decisions in the wake of the comments received on the draft version was published on June 6.

The guideline outlines five main principles for prudent mortgage underwriting, providing that firms must: have a comprehensive residential mortgage underwriting policy; perform reasonable due diligence to assess a borrower’s identity, background and demonstrated willingness to service their debt obligations on a timely basis; adequately assess the borrower’s capacity to service their debt obligations on a timely basis; have sound collateral management and appraisal processes; and have effective credit and counterparty risk management, including, where appropriate, mortgage insurance.

Earlier this month, in detailing some of its policy decisions, OSFI said that it is sticking with its position that the home equity line of credit (HELOC) component of a mortgage should be restricted to a maximum loan-to-value ratio of 65%. However, HELOCs that are at, or below, 65% will not be required to be amortized. It also said that, among other things, it would maintain the proposed new disclosure requirements; and, that financial institutions will remain responsible for deciding what level of review to place on borrowers’ qualifications when they renew a mortgage, but they will be expected to refresh the borrowers’ credit metrics periodically (not necessarily at renewal) so that they can effectively evaluate their credit risk.

Full implementation of the new guideline is expected by the end of fiscal 2012, with the relevant public disclosures beginning in the first quarter of 2013, OSFI said Thursday.

OSFI notes that the deadline will allow time for firms to implement any systems or process changes that may be required. But, in the meantime, it says that firms should conduct self-assessments of compliance with the revised guideline and establish a plan to address any deficiencies. It also notes that the guideline will not be applied on a retroactive basis to existing in-force residential mortgages.