Mortgages master trusts

Losses in master trust mortgage transactions can be recorded as an annualised charge-off rate in a similar manner to the standard method in credit card transactions. However, losses on prime mortgages are generally very small and intermittent so this measure will tend to be relatively volatile. The results for the Holmes Financing transaction provide a good illnstra-tion of this point (see Exhibit 11.16). 

The structure of a mortgage master trust is essentially identical to a credit card master trust except that credit card receivables are replaced with mortgage collateral (see Exhibit 11.13). The originator sells an equitable interest in a specified group of mortgages to the master trust. This can then be used as collateral for a number of securitisations. Over time, additional mortgages may be added to the trust, subject to various constraints to protect the quality of the collateral. The same pool of mortgages will support all the series of notes issued by all issuers, with... 

Mortgage master trusts require the seller to maintain a certain minimum interest in the collateral pool held by the master trust. In credit card transactions this is used to absorb the monthly fluctuations in the balance outstanding on the credit cards and ensure there is always sufficient collateral to support the notes. In RMBS transactions the minimum seller s interest tends to be smaller as the mortgages have a more stable repayment profile, and this is primarily available to cover set-off risk in the event of originator insolvency. In existing transactions it is the minimum trust size rather than the minimum seller s share that has been the key constraint. 

The calculation of credit enhancement for notes in a master trust transaction seems more complicated than in a traditional pass-through transaction because subordinated notes from an earlier series are expected to be redeemed before the senior notes of later series. However, if the mortgages were to perform poorly, the trigger events ensure that all outstanding junior notes would only be repaid after all the senior notes. So the credit enhancement can be calculated as the aggregate balance of subordinate notes as a proportion of the total notes outstanding. 

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