Five hundred hardy families is the extent of the market opened up, to date, by Rismark International in their quest to make co-investment in the family home by outsiders a viable financing option.With an investment pool of around $200 million under management at present, that suggests the average size of a "shared equity" loan funded by Rismark is around $400,000 and that the average value of family homes funded by the firm is more than $1 million.Under a shared equity loan a home owner sells a minority stake to a Rismark fund. The owner must repay the loan in 20 years, or when they sell or refinance the loan. Rismark has the right to a share of any capital gain at the time of sale or refinance. In the case of a house purchase, but not a refinancing, Rismark will also share in any loss of capital.Rismark disclosed the number of borrowers in connection with the announcement, on Friday, of additional investment by Macquarie Group in the firm and also in the firm's managed fund.Macquarie will take a 53 per cent stake in Rismark. The level of Macquarie's investment in the fund is not clear but is described as substantial.One other investor in the fund is Bendigo and Adelaide Bank, which also provides conventional first mortgage finance to most of the households that have made use of the Rismark shared-equity scheme.Rismark is the only firm that managed to bring a share equity loan to market, back in 2007, following several years of effort by a handful of companies. A couple of state governments promote co-ownership of family homes in conjunction with state housing authorities, but shared ownership of residential housing stock by institutional investors is extremely rare.Rismark says its returns, based on house price indices it helped develop, exceeded returns for many other asset classes over the year. The firm says it targets returns of between 12 and 15 per cent a year.