Freddie Mac, the country’s largest backer of apartment loans, will offer low-cost loans to real-estate owners willing to keep their buildings affordable to middle-class families for years to come, the Wall Street Journal reported. The move could open up a new approach to creating and preserving middle-class housing. It uses market incentives rather than government subsidies to persuade real-estate companies to preserve units for the middle of the rental market, an area of concern for policy makers in recent years. “The supply of workforce housing is rapidly declining. There’s an urgent need to preserve what’s there and find ways that you can effectively create more,” said David Brickman, an executive vice president at Freddie Mac and head of its multifamily division. The initiative will offer lower interest rates to landlords who agree to rent the majority of units in a building at levels affordable to tenants making 80 percent or less of the area’s median income, a range that typically includes nurses, teachers and police officers. The units must remain affordable for the term of the loan, typically about a decade.