Lending to residential property investors is back in positive territory in the Reserve Bank's lending data for the first time since December 2018.According to the RBA, the investor housing finance component of lenders' mortgage books increased by 0.1 per cent in January. It had been flat or negative in each of the previous 12 months.Overall, lenders' mortgage portfolios grew by 0.3 per cent in January, compared with the previous month and by 3.1 per cent over the 12 months to January.Owner occupier loan balances grew by 0.4 per cent in January and by 5.1 per cent over 12 months.Residential property investor balances grew by 0.1 per cent in January but fell by 0.3 per cent over 12 months.According to the most recent Australian Bureau of Statistics figures, new lending to investors rose for three consecutive months to December but is still well below the peak of activity in 2017.