One-third of all housing in Montgomery County is rental units, and affordability is becoming a chief concern for the area’s residents, according to a study the Montgomery Country Planning Department presented Thursday.

Half of Montgomery Country renters spent over 30% of their income on housing, UrbanTurf reports. This cost burden is particularly tough on those making between 30% and 50% of the county’s $110K median annual income. Older rental developments are more affordable, but high demand and lower post-recession incomes are causing that affordability to dwindle.

One reason for the lack of affordable housing is that those earning more than 120% of the average area income are choosing to live in rentals well under what they can afford. Demand for rental housing is up as millennials and those on the younger side of Generation X look to cut costs and people who could otherwise afford a home choose to rent rather than take on the perceived burden of homeownership.

As for where renters are going, location depends on age. The study showed transit-oriented development is a millennial-driven trend, with those aged 25 to 34 prefer high-density development like those seen inside I-495 and along I-270. Respondents who were 65 and older preferred wealthier, suburban settings.

The study did provide some solutions for making Montgomery County rental units more affordable. It recommends boosting the affordable housing requirement from 12.5% to 15% while providing developer incentives for preservation or adaptive reuse of existing structures.