Demand for fixed-rate mortgages has fallen steadily over the past year, as borrowers bet on an extended period of low rates and opt for variable-rate mortgages.According to the latest Australian Bureau of Statistics Housing Finance data, the proportion of fixed-rate loans among new housing finance commitments in June was 14.3 per cent, compared with 14.9 per cent in May. The number has fallen steadily from 17.9 per cent in June last year.These numbers raise questions about why the big banks went so hard on marketing five-year fixed rate reductions last month. The impact on the market would be negligible.The ABS figures show that the value of housing finance commitments rose one per cent in June, compared with the previous month (in seasonally adjusted terms).The increase followed a fall of 0.8 in the value of housing finance commitments in May.Since the start of the year the monthly value of new housing finance commitments has increased from A$26.8 billion in January to $27.7 billion in June - an increase of 3.4 per cent.The value of new loans to owner-occupiers rose 1.8 per cent in June, while the value of loans to residential property investors fell 0.3 per cent.This is a reversal of the recent trend, where investors have led to growth in the housing finance market.The number of owner-occupier housing finance commitments rose 0.2 per cent in June.The average loan size has climbed from $304,500 to $327,000 in the 12 months to June - an increase of 7.4 per cent.