SAN FRANCISCO (CBS SF) — The tight rental market isn’t just putting the squeeze on residents in the Bay Area as new research from Harvard shows that low and even moderate-income earners are facing affordability issues across the country.

The study found that the nearly half of all renters in the U.S. are considered “cost burdened.”

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“Between 2001 and 2014, real rents rose 7 percent while household incomes fell by 9 percent. In combination, these trends pushed the number of cost-burdened renters (paying more than 30 percent of income for housing) up from 14.8 million to a new high of 21.3 million,” the authors wrote.

Maybe unsurprisingly, the sharpest growth in the cost-burdened category is among middle-income earning renters pulling in $30,000-$44,999 annually, and certain age groups.

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“Burdens are most prevalent among the youngest (under age 25) and oldest (aged 65 and over) renter households.”

The market has yielded big returns for landlords, but as residents spend an increasing amount of their income on rent, the task of saving for a down payment is becoming more difficult.

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In the third quarter of 2015 alone, average rents in the U.S. increased more than 5 percent, while in the Bay Area prices jumped 10 percent, or more.