The RBA has published a paper on Structural Features of Australian Residential Mortgage-backed Securities. It provides a useful overview of the securitisation market in Australia, which is one important element in product funding. We have summarised some of the key points.
A residential mortgage-backed security (RMBS) is a collection of interrelated bonds that are secured by a dedicated pool of residential mortgages (the ‘mortgage collateral pool’). The payments of principal and interest on these bonds are funded from the payments of principal and interest made on the underlying mortgage collateral by the mortgagors. Historically, RMBS have provided an alternative to bank deposits as a source of funding for residential mortgages. This has been particularly important for smaller authorised deposit-taking institutions (ADIs) and non-ADIs that have limited access to deposit funding or term funding markets.
By allowing smaller institutions to raise funding in the capital markets, RMBS promote competition between lenders in the residential mortgage market. After increasing steadily in the early 2000s, issuance of Australian RMBS to third-party investors fell in the wake of the global financial crisis when these securities were adversely affected by a loss of confidence in the asset class globally despite the low level of mortgage defaults in Australia. The market has recovered somewhat over the past couple of years.
RMBS have been an eligible form of collateral in repurchase agreements (repos) with the RBA since 2007. During the height of the global financial crisis, RMBS formed a significant part of the RBA’s repo collateral and hence played an important role in the RBA’s response to the crisis. Currently, RMBS form the largest class of securities held under the RBA’s repos, although unlike the earlier episode, this has been in response to innovations in the payments system. From 1 January 2015, the RBA has provided a Committed Liquidity Facility (CLF) to eligible ADIs as part of Australia’s implementation of the Basel III liquidity standards. In total, the CLF provides ADIs with a contractual commitment to $275 billion of funding under repos with the RBA, subject to certain conditions. Given that RMBS are eligible collateral that could be provided to the RBA were the CLF to be utilised, they represent a substantial contingent exposure for the RBA and, hence, understanding RMBS is particularly important in terms of managing the RBA’s balance sheet.
While discussions of RMBS often focus on the mortgage collateral pool, as all payments to investors are made from the cash flows generated from this pool, the structural features of RMBS play an equally important part in determining the risks facing the holders of these securities. The ‘structure’ of an RMBS refers to the number and size of the interrelated bonds of the RMBS, the rules that determine how payments are made on these bonds and various facilities that support these payments.
This article provides a summary of the structural features typically found in Australian RMBS and how these have evolved over the past decade.
One element of note is tranching.
In summary, tranching enhances one part of the RMBS liability structure at the expense of another, by reducing credit and prepayment risk on the senior notes, while increasing these risks for the junior notes. Since 2005, there has been an increase in the degree of tranching in Australian RMBS. The average number of notes in an RMBS has increased from three in 2005 to four in 2015, with most of the increase occurring after 2008. The increase has been concentrated in the junior notes (which are typically rated below AAA), with the average number of such notes increasing by 1.5 per RMBS. The increase has been more pronounced in RMBS issued by non-ADIs.
The higher number of tranches for RMBS issued by non-ADIs reflects the need for non-ADI sponsors to fund their mortgage lending fully through RMBS issuance. This has led RMBS issued by non-ADIs to be structured with a larger number of tranches with different characteristics that appeal to a broad range of investor risk appetites.
The structures of Australian RMBS have evolved over time. Australian RMBS have generally become more structured over the past 10 years, especially since the global financial crisis: the tranching of both credit and prepayment risk has increased; the use of principal allocation mechanisms that vary over the life of the RMBS has become more widespread; bullet notes have been added; and various external and internal support facilities have continued to be used.
The increased structuring, which has developed to address changing market conditions, does not necessarily create more risk for investors, especially if they are provided with transparent and complete information about RMBS structures. Indeed, there has been a significant increase in the size of the credit enhancement provided to the most senior notes through the subordination of junior notes, with the increase in excess of the requirements of the credit rating agencies. The reliance on external credit support from LMI has also declined.
Understanding RMBS structures is essential to the effective risk management and valuation of RMBS because the RMBS structure determines how the risks generated from the securitised mortgages are borne by each particular RMBS note. Given the importance of RMBS as collateral in the RBA’s repurchase agreements, the RBA has a keen interest in understanding RMBS structures.
The RBA’s reporting requirements for repo-eligible asset-backed securities, which come in effect from 30 June 2015, will provide standardised and detailed information, not only on the mortgages backing RMBS, but also on the RMBS structures, including their cash flow waterfalls.
