The role of residential property investors in driving growth in the mortgage market was underlined by aggregator AFG yesterday, when it reported that investors accounted for 38.7 per cent of loans written by its brokers in August. Investor activity was at its highest level for the year.The proportion of loans being sold to investors has increased by four percentage points since February, when 34.7 per cent of loans written by AFG brokers were for investors.Investor activity was particularly strong in New South Wales, where 49.5 per cent of AFG loans were for investors. According to Reserve Bank figures released on Friday, the value of investor loans rose by 0.4 per cent in July and by 5.8 per cent over the 12 months to July.Owner-occupier loans were up 0.3 per cent in July and up 4.1 per cent over the 12 months.Total housing finance commitments were up 0.4 per cent in July and up 4.7 per cent over the 12 months. The annual growth rate has crept up from 4.4 per cent earlier in the year.AFG brokers wrote 8767 mortgages in August, worth A$3.6 billion. The average loan size was A$412,000 and the average loan-to-valuation ratio was 68.2 per cent.First-home buyer activity was a modest 11.3 per cent.