C3-5-01, Creating Weighted-Average ARM MBS (08/26/2014)

ARM Flex pools provide interest accruals at a weighted-average pool accrual rate to the holders of securities backed by the ARMs in the pool. These pools may be delivered only as single pool transactions and different standard ARM plans may not be commingled in the same pool.

The original term of an ARM included in a weighted-average ARM MBS pool must be no more than 30 years. Each mortgage must accrue interest in arrears and have a payment due date of the first day of the month. There is no restriction on the range of first payment due dates, interest rate change dates, and payment change dates.

To limit the effect that prepayments have on the weighted-average pool accrual rate of an ARM Flex, lenders should consider limiting to 1% (100 basis points) the range between the lowest and highest mortgage margins and the lowest and highest mortgage interest rate ceilings of all the mortgages in the pool.

Under the ARM Flex pooling structure, lenders may create a weighted-average ARM MBS using either the

• fixed MBS margin or

• weighted-average MBS margin.

The difference between the two margin types is the method used to determine the interest rate that accrues on the pool and the retained servicing fee. The fixed MBS margin option is based on a pool-level MBS margin and a loan-level servicing fee. This means that when the pooled mortgages have different mortgage margins, the servicing fees for the mortgages vary in order to equalize the differences in the mortgage margins. While the guaranty fee remains the same, the servicing spread (the sum of the servicing fee and the guaranty fee and, if applicable the periodic renewal premium for lender-purchased mortgage insurance) differs from mortgage to mortgage.

The fixed MBS margin applies to each mortgage in the weighted-average ARM MBS; therefore, the lowest mortgage margin in the pool must be able to, at least, support the sum of the MBS margin, the guaranty fee, and the minimum allowable servicing fee. The periodic renewal premium for lender-purchased mortgage insurance must also be included, if applicable.

The weighted-average MBS margin option is based on a pool-level servicing fee and a loan-level MBS margin, which means that when the mortgages in the pool have different mortgage margins, the servicing spread will be equal for all the mortgages, but the MBS margin will vary from mortgage to mortgage.