Brief: NAB launces RMBS 04 March 2015 4:14PM Banking Day staff National Australia Bank has launched an issue of residential mortgage backed securities, seeking A$750 million of funds. National RMBS Trust 2015-1 is backed by a portfolio of mortgages with an average loan-to-valuation ratio of 64.2 per cent and an average loan size of $293,511. Investment loans make up 20.2 per cent of the pool and interest-only loans 23.4 per cent.