Bank of Queensland grew its mortgage book at almost twice the rate of system growth during the six months to February, underpinning seven per cent growth in earnings for the half.According to APRA data, at the end of February BOQ had A$29.9 billion of mortgages on its books - an increase of 5.7 per cent over six months. This is well ahead of system growth of 3.5 per cent over the same period.Total loans and advances grew ten per cent to $42.6 billion over the same periodBOQ chief executive Jon Sutton said the bank had expanded its broker distribution network and made changes to the branch network. BOQ sells through 3200 accredited brokers. The majority of brokers are outside Queensland and two-thirds of originations during the half were outside the state.The bank reported net profit of $171 million for the six months to February - an increase of 11 per cent over the previous corresponding period. On a cash basis, profit was up seven per cent to $179 million.Earnings per share rose five per cent to 47.8 cents a share, on a cash basis.Return on equity rise from 10.3 per cent in the February half last year to 10.5 per cent in the latest half.Net interest income rose four per cent to $467 million and non-interest income rise one per cent to $85 million.The net interest margin was flat at 1.97 per cent. Operating expenses were unchanged at $256 million. The cost-to-income ratio fell from 48.1 per cent in the February half last year to 46.1 per cent in the latest half.The loan impairment expense was also unchanged at $36 million. Loan impairments as a percentage of gross loans and expenses fell from 18 basis points to 17 bps.Arrears past due by 30 days or more rose five per cent to $562 million but arrears last due by 90 days or more fell two per cent to $255 million.