What it means
The structure is best understood by comparing it with securitisation. In a securitisation the bank sells loans away to a separate vehicle and investors depend on those loans alone, whereas in a covered bond the loans stay with the bank, the bank remains fully liable, and the pool is an additional layer of protection rather than the only one.
Investors call this dual recourse. The pool is dynamic, which is a crucial detail.
If loans in it default, fall into arrears or are repaid early, the issuing bank must replace them with performing loans so the pool always exceeds the bonds outstanding by an agreed margin. This continuous substitution is the mechanism that keeps the collateral quality high over the life of the bond.
For banks, the attraction is cheap, long-dated funding for their mortgage books, particularly in markets where deposits alone cannot fund lending growth. For investors, especially insurers and pension funds, the attraction is a high quality, long-dated asset that pays more than government debt while enjoying favourable treatment in most regulatory capital and liquidity rules.
The margin of protection is measured as overcollateralisation, the extent to which the value of the pool exceeds the bonds it backs. Legal minimums exist in most jurisdictions, but issuers usually run well above them to satisfy the rating agencies and to leave room for house price falls or arrears.
Two nuances shape how these bonds behave in practice. Most European covered bond frameworks are set out in specific legislation that determines what can enter the pool and how it is treated in an insolvency, and many modern deals include soft bullet or conditional pass-through features that extend the maturity rather than defaulting if refinancing proves difficult.
In practice
Real-world examples.
Example
A mortgage lender funds its growing loan book by issuing $500,000,000 of seven-year covered bonds. The rate it pays is well below what it would pay on ordinary senior unsecured debt, because investors are pricing the collateral as well as the bank.
Example
An insurance company matching long-term annuity liabilities buys covered bonds instead of government bonds. It picks up extra yield while keeping an asset that its regulator treats favourably for capital purposes.
Example
A bank's treasury team monitors the cover pool monthly. When arrears rise in one region, it substitutes those mortgages out of the pool and replaces them with newer performing loans to keep the overcollateralisation level steady.
Formula
Calculation
Overcollateralisation = (Value of the cover pool - Value of bonds outstanding) / Value of bonds outstanding, expressed as a percentage.
A bank has issued $800,000,000 of covered bonds. The ring-fenced cover pool contains residential mortgages with an eligible value of $920,000,000.
Overcollateralisation = ($920,000,000 - $800,000,000) / $800,000,000 = $120,000,000 / $800,000,000 = 0.15, or 15%. In plain terms, there is $1.15 of eligible mortgage collateral behind every $1.00 of bonds.
Now stress the pool. If house prices fall 10%, the eligible pool value drops to $828,000,000 and overcollateralisation becomes ($828,000,000 - $800,000,000) / $800,000,000 = 3.5%. If the legal minimum in that jurisdiction is 5%, the bank must add roughly $12,000,000 of further eligible mortgages to the pool to restore compliance, since $840,000,000 of collateral is needed to support $800,000,000 of bonds at 5%.Case study
Seen in the real world.
Ashvale Mortgage Bank is a fictional lender created purely for this illustrative example. Its deposit base was growing more slowly than its mortgage lending, and issuing ordinary senior debt had become expensive after a downgrade of its credit rating.
The treasury team assembled a cover pool of $920,000,000 of prime residential mortgages, all with loan to value ratios below 70%, and issued $800,000,000 of five-year covered bonds. Overcollateralisation at issue was 15%, and because investors also had recourse to the bank itself, the bonds priced well inside what the bank was paying on its unsecured debt.
Two years later a regional housing correction cut pool values by around 10%, taking overcollateralisation to 3.5% and below the legal minimum. Ashvale had to move roughly $12,000,000 of additional performing mortgages into the pool at short notice. In this invented example the structure worked exactly as designed, but it reminded the treasurer that a covered bond is a continuing obligation to maintain collateral, not simply a funding event on the day it is priced.
Watch out
Common mistakes.
- Treating covered bonds as just another name for mortgage-backed securities. The loans stay on the issuing bank's balance sheet and the bank stays liable, which is precisely the difference that gives investors two claims instead of one.
- Ignoring the ongoing collateral obligation. Falling property values or rising arrears force the issuer to top the pool up, which uses assets and liquidity at exactly the moment they are scarce.
- Assuming the headline overcollateralisation is fixed. It moves with house prices, arrears and prepayments, so the figure quoted at issue is a snapshot rather than a permanent feature.
Questions
People also ask.
Why do covered bonds pay less than a bank's other debt?
Because investors hold claims both on the bank and on a ring-fenced pool of quality loans, so the expected loss is much lower.
What happens to the pool if the bank fails?
Under most covered bond laws the pool is separated from the general insolvency estate and used to keep paying bondholders, with any surplus later returning to the estate.
Can anything other than mortgages back a covered bond?
Yes, public sector loans and, in some jurisdictions, ship or aircraft loans are permitted, though residential mortgages dominate the market.
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