Lenders should not expect lending to self-managed superannuation fund trustees to be any more than a niche market, but it is a sector that offers growth. This is the conclusion of research company RFi, which has taken a look at the potential of the SMSF loan market.According to an RFi survey of SMSF trustees, property makes up 15 per cent of the assets of self-managed funds, on average. This tallies with Australian Taxation Office research, which shows that, at June 2011, SMSFs had an average of 11.4 per cent of their assets in non-residential property and 3.5 per cent in residential property.Of the respondents to the RFi survey who said they had property, 27 per cent had a loan.RFi's Australian research director, Alex Boorman, said: "Property investment in SMSFs is likely to increase. Fifteen per cent of trustees said they had increased their allocation to property in the past 12 months "Twenty-one per cent told us they planned to increase their allocation to property over the next 12 months."Boorman, who was speaking at RFi's Australian Mortgage Conference in Sydney, on Friday, said there was an opportunity for lenders, but they had to recognise that the market was constrained by a number of factors.One is complexity. The ATO has ruled that SMSF loans must be limited recourse, to protect other assets of the fund. The property must be held in a separate trust until the fund has finished paying for it. In addition, owners must not make substantial changes to their properties while they are encumbered.Another constraint RFi identified was that SMSF trustees are prone to inertia. Once they have set up their fund and decided on an investment strategy they tend to leave things unchanged.Boorman said the best opportunity for lenders was to work with advisers to introduce the idea of geared investing during a fund's establishment stage.