Australian mortgage-backed securities

Australian mortgage-backed securities are debt instruments backed by pools of Australian residential mortgage loans. They are mainly issued through special purpose vehicles by banks and non-bank lenders, with investors receiving payments funded by mortgage principal and interest collections. In Australia the term most commonly refers to residential mortgage-backed securities, or RMBS.

Overview

Australian mortgage-backed securities form the largest segment of the country’s securitisation market. In securitisation, loan cash flows are pooled and used to pay multiple classes of creditors, usually through securities with different seniority and credit risk. APRA’s prudential standard defines securitisation as a financing structure in which cash flow from a pool is used to make payments on obligations to at least two tranches or classes of creditors, with each tranche entitled to payment before or after another class, reflecting different levels of credit risk.^[1]

In a typical Australian RMBS transaction, a lender sells or assigns a pool of residential mortgages to a special purpose vehicle, often structured as a trust. The trust issues notes to investors. The senior notes have first claim on available mortgage cash flows after specified transaction costs and are generally designed to have lower credit risk than mezzanine or subordinated notes. Subordinated tranches, excess spread, lenders’ mortgage insurance, cash reserves and other structural features may provide credit support, depending on the deal.

The Australian market includes both “marketed” RMBS sold to investors and “self-securitisations” retained by originating authorised deposit-taking institutions. APRA defines a self-securitisation as a securitisation solely for using the securities created as collateral to obtain funding through a repurchase agreement with the Reserve Bank of Australia.^[1] The distinction matters because marketed RMBS are funding instruments sold to capital-market investors, while self-securitisations are primarily liquidity-management instruments.

Issuers and market role

Issuers include major banks, regional banks, mutual banks, credit unions, building societies and non-bank mortgage lenders. For banks, RMBS can diversify funding beyond deposits, wholesale senior debt and covered bonds. For smaller lenders, securitisation may provide access to investors that would otherwise be difficult to reach directly. For non-bank mortgage lenders, securitisation is structurally more central because such lenders do not take deposits.

The RBA has described RMBS as the “staple” of the Australian asset-backed securities market, stating in 2024 that RMBS accounted for about three-quarters of the Australian ABS market.^[2] The same RBA speech noted that non-banks had become more prominent: the number of non-bank ABS issuers in Australia had risen four-fold from a decade earlier, and non-banks had accounted for most ABS issuance in recent years.^[2]

The growing role of non-banks affects the composition of mortgage pools. The RBA has observed that securitised residential mortgages have shifted toward investor loans and low- or alternative-documentation loans, largely reflecting the increased market share of non-bank lenders that target these segments more than banks.^[2] At the same time, the RBA noted a shift away from high loan-to-valuation-ratio lending and interest-only lending, which may offset some credit-risk indicators.^[2]

Structure and cash flows

Australian RMBS transactions are usually structured around a trust that holds the mortgage pool and issues notes. Borrowers continue to make mortgage payments to the loan servicer. The servicer collects payments, manages arrears and remits cash into the securitisation structure. The transaction documents establish a payment waterfall: senior expenses and hedging costs are paid first, followed by interest and principal on the most senior notes, then lower-ranking notes, and finally any residual income after all required payments.

Tranching is central to RMBS. A senior tranche is designed to be paid before subordinate tranches and therefore generally has greater protection against mortgage losses. Subordinate tranches absorb losses earlier and are compensated with higher coupons. Some deals include liquidity facilities, redraw facilities or reserve accounts to manage timing mismatches between mortgage receipts and note payments. Because Australian home loans commonly allow variable interest rates, offset accounts, redraws and prepayments, RMBS structures also address prepayment risk and basis risk.

Australian RMBS may include fixed-rate, variable-rate, owner-occupier, investor, principal-and-interest, interest-only, prime, near-prime and non-conforming loans, depending on the issuer and transaction. Investors analyse pool stratification by borrower type, geographic location, seasoning, loan-to-valuation ratio, debt-to-income measures, documentation type, repayment type and arrears history. Rating agencies also assess legal isolation of assets, servicing arrangements, operational risk, cash-flow stress scenarios and counterparty exposures.

Regulation and prudential treatment

Australian RMBS sit within a broader framework covering banking prudential regulation, market disclosure, consumer credit law and central-bank collateral rules. For authorised deposit-taking institutions, Australian Prudential Regulation Authority Prudential Standard APS 120 Securitisation is the central prudential standard. The current APRA instrument commenced on 1 January 2024 and applies to ADIs and authorised non-operating holding companies to the extent provided in the standard.^[1]

APS 120 covers securitisation roles and investments of ADIs, whether the underlying exposures were on an ADI’s balance sheet, originated by an ADI into the pool, or originated by another entity. It applies capital requirements to securitisation exposures held in the banking book and also addresses traditional, synthetic and hybrid securitisations.^[1] The standard requires separation between the originating ADI and the securitisation. It states that securities issued by the special purpose vehicle must not be obligations of the ADI, and investors may only have a claim on the relevant pool and applicable facilities of the SPV.^[1]

APRA also restricts implicit support. An originating ADI must not provide or encourage a perception that it will provide support beyond its contractual obligations.^[1] The standard requires disclosure to investors about the nature and limits of an ADI’s obligations and requires legal isolation of exposures transferred to a securitisation structure.^[1] These rules are designed to ensure that risk transfer, funding treatment and capital treatment reflect the economic substance of the transaction.

Australian Securities and Investments Commission is relevant where RMBS are offered under securities laws, where disclosure documents are required, or where market conduct and financial-services licensing obligations apply. Consumer credit rules also shape the mortgage loans that ultimately enter RMBS pools, although RMBS investors have exposure to the securities rather than direct lender rights against borrowers.

RBA collateral and data requirements

The Reserve Bank of Australia accepts eligible asset-backed securities, including RMBS, as collateral in domestic market operations subject to eligibility criteria. This makes RMBS important not only as market funding instruments but also as liquidity-management assets. The RBA requires extensive information on underlying loans for asset-backed securities seeking repo eligibility. Its reporting guidelines require a single XML file per deal per month covering loan-level, security-level, transaction-level, pool-level, cash-flow waterfall model and related data.^[3]

The RBA also requires relevant securitisation data to be made available to permitted users, including parties interested in asset-backed securities for investment purposes and professional or academic research.^[3] Securities that lose eligibility because of late reporting remain ineligible until outstanding submissions have been made and a subsequent submission has been completed successfully by the due date.^[3] These requirements have contributed to a comparatively detailed data environment for Australian RMBS analysis.

The RBA’s Securitisation Dataset contains both marketed RMBS and self-securitisations. As at May 2024, it contained about 1.7 million individual mortgages with a scheduled balance of almost A$700 billion, representing roughly one-third of total outstanding Australian housing credit by value.^[4] The RBA reported that about 92% of balances in the dataset were from ADIs, around 85% were from major banks’ self-securitisations, and the remaining 15% were marketed securities split between ADIs and non-bank financial institutions.^[4]

The RBA uses the dataset primarily to assess the financial risk of RMBS and their suitability as collateral. It also uses the data as a secondary source for monitoring risks in the residential mortgage market.^[4] The central bank cautions, however, that securitised mortgage pools may differ from the broader mortgage market because issuers have incentives when selecting loans for securitisation and because new loans can be underrepresented due to securitisation lags.^[4]

Self-securitisation

Self-securitisation is a distinctive feature of the Australian market. In these transactions, an ADI structures a pool of mortgages into securities but retains the notes rather than selling them to investors. The purpose is to create collateral that can be used in repurchase transactions with the RBA. APRA’s APS 120 requires an originating ADI of a self-securitisation to treat it as a funding-only securitisation and to comply with operational requirements from the time the securities are used as RBA repo collateral.^[1]

Self-securitisations became especially visible during periods of market stress and central-bank liquidity support. Because they are not sold to investors, they do not provide market funding in the same way as public RMBS. Instead, they transform otherwise illiquid mortgage pools into securities that can be pledged to the RBA if eligibility conditions are met. The RBA has noted that self-securitisations are not sold to investors but are held entirely by originating ADIs for use as collateral in RBA market operations, including the Term Funding Facility.^[4]

Self-securitisations also create analytical issues. They dominate the RBA Securitisation Dataset, so changes in the composition of self-securitised pools can affect aggregate measures such as arrears or borrower characteristics. The RBA has warned that trends in arrears of self-securitised loans need caution because compositional changes can lead to divergences between dataset arrears and the broader mortgage market.^[4]

Investors and pricing

Investors in Australian RMBS typically include banks, insurance companies, fund managers, pension and superannuation investors, offshore institutional investors and other fixed-income buyers. RMBS are commonly assessed relative to bank senior debt, covered bonds, Australian dollar corporate bonds and other asset-backed securities. Pricing reflects credit risk, prepayment assumptions, structure, seniority, collateral quality, issuer reputation, ratings, liquidity, swap arrangements and broader credit-market conditions.

Australian RMBS are usually floating-rate instruments, often linked to short-term benchmark rates such as the bank bill swap rate. Floating-rate coupons reduce duration exposure compared with long fixed-rate bonds, although investors remain exposed to credit spreads, prepayments, basis risk and liquidity risk. Senior notes in prime RMBS may be treated by investors as high-grade structured credit, while mezzanine or subordinated notes carry greater sensitivity to arrears, house prices and unemployment.

For issuers, RMBS pricing determines whether securitisation is attractive relative to alternative funding. Non-bank lenders are particularly sensitive to warehouse funding costs and term securitisation spreads because they rely more heavily on wholesale markets. The RBA stated in 2024 that RMBS made up an estimated three-quarters of funding for Australian non-bank mortgage lenders.^[2]

Public-sector support and stress episodes

Australian RMBS issuance was materially affected by the global financial crisis, when investor demand for structured credit weakened sharply. During that period, the Australian Office of Financial Management was directed by the Australian Government to invest in RMBS to support competition and liquidity in the mortgage market. Treasury material released under freedom-of-information processes states that A$20 billion was made available under Treasurer directions and about A$15.5 billion was invested in AAA-rated RMBS between late 2008 and mid-2012.^[5]

Public-sector involvement reappeared during later stress periods, including the early COVID-19 pandemic, through liquidity and funding measures rather than a permanent government guarantee of RMBS. Australia does not have a government-sponsored mortgage securitisation framework equivalent to the U.S. agency model associated with the Federal National Mortgage Association. Australian RMBS investors generally rely on the transaction structure, collateral pool, credit enhancement and legal documentation, not a standing sovereign guarantee.

Data, size and measurement

The Australian Bureau of Statistics publishes quarterly data on assets and liabilities of Australian securitisers. Its scope includes resident special purpose vehicles that issue asset-backed securities using selected asset pools and explicitly excludes internal securitisation.^[6] This means ABS data on securitisers is useful for measuring market-issued securitisation but does not capture the full stock of self-securitised collateral structures retained by banks.

Because “Australian mortgage-backed securities” can refer to marketed RMBS, eligible repo collateral, self-securitisations, or the broader mortgage component of securitiser assets, reported market sizes vary depending on the definition. Analysts therefore distinguish between issuance, outstandings, public-market deals, private placements and internal self-securitised pools. The RBA’s collateral dataset is broader in some respects than public issuance statistics because it includes self-securitisations, while the ABS securitiser series is narrower in that it excludes internal securitisation.^[4][6]

Risks and analytical considerations

The main risks in Australian RMBS include mortgage credit risk, house-price risk, unemployment risk, interest-rate and refinancing stress, prepayment risk, servicer risk, counterparty risk, documentation risk and market liquidity risk. Credit losses depend on both borrower default and loss severity after property sale and enforcement costs. Australia’s full-recourse mortgage lending, underwriting practices and lender mortgage insurance may affect loss outcomes, but none eliminates risk.

Interest-rate increases can pressure variable-rate borrowers and increase arrears, while falling interest rates can increase prepayments and shorten expected note life. Geographic concentration matters because housing downturns can be regional. Investor-loan and interest-only exposures may perform differently from owner-occupier principal-and-interest loans. Low-documentation and non-conforming pools require separate analysis because borrower verification and historical arrears behaviour can differ from prime bank-originated pools.

Liquidity risk is also important. Even senior RMBS can become difficult to trade during market stress. Self-securitisations are less liquid because they are not publicly traded and are designed for collateral use rather than investor distribution. The RBA has previously described self-securitisations as large relative to outstanding public RMBS, illiquid and not traded on a public market.^[7]

Relationship to Australian housing finance

RMBS link Australia’s housing finance system with domestic and global capital markets. They allow mortgage lenders to convert pools of home loans into tradable securities and can increase competition by supporting lenders without large deposit bases. They also provide institutional investors with exposure to diversified mortgage cash flows and structured credit tranches.

At the same time, RMBS are not a substitute for mortgage underwriting. The quality of the securities ultimately depends on loan origination standards, collateral values, servicing and macroeconomic conditions. Australian regulators and the RBA monitor securitisation because it affects bank funding, non-bank lending, monetary operations, investor risk and financial stability. The market’s importance is therefore both private and systemic: RMBS are instruments for funding individual lenders, but they also form part of the infrastructure through which Australian housing credit is financed and assessed.