This week, Harvard’s Joint Center for Housing Studies and the affordable housing organization Enterprise Community Partners released a report sketching out various scenarios of rental cost and income growth for the next ten years. The headlines are fairly bleak: JCHS and Enterprise project the number of “severely rent-burdened” households to grow under almost any scenario. (The report uses the common definition of households paying more than half of their income for housing as “severely rent-burdened.” About which more at the end of this post.) Even if income growth moderately outpaces rent increases—something that hasn’t happened for over 20 years—demographic trends, including the rising number of elderly households, will push the severely rent-burdened totals higher.

But a few other parts of the report stick out, too.

For one, JCHS and Enterprise write that there is a huge national rental supply crunch, which is a major source of rising rents. The paper notes that while the number of rental households is growing at record levels, the growth of rental housing units is lower than it’s been for generations. JCHS projects that there will be 4.2 million more rental households ten years from now—though it notes that may be an underestimate, as the Urban Institute has placed its guess closer to 6 million. But in the last ten years—in large part because of the Great Recession—the number of rental homes grew by only 2.2 million, a pace slower than any since the early 1970s. As a result, vacancy rates are historically low, putting upward pressure on rental prices.

Second, a huge proportion of the growth in rental households in every scenario that JHCS and Enterprise sketched out is made up of single people. Partly, that’s Millennials putting off having families. But it’s also in large part about the growing number of elderly adults, and especially elderly women, living alone. While much of the discussion and debate about “tiny houses” or “microapartments” centers on the lifestyles of young, highly mobile, relatively wealthy urbanites, this report is a reminder that many of the housing types we’ve made illegal in our neighborhoods—the studios, small one-bedrooms, and backyard cottages—are needed by, and have historically served, a broad range of demographics. In other words, they’re called “granny flats” for a reason: because the elderly as well as the young have relied on a small, flexible, affordable housing types to remain living independently in the communities they value. As the number of single households, and single renters, continues to grow, making sure we haven’t outlawed the kinds of housing they need is a key challenge.

Finally, we feel the need to note that, like the 30 percent housing-cost-to-income ratio that usually denotes “cost-burdened,” the 50 percent ratio that JCHS and Enterprise used to denote “severely cost-burdened” suffers from some serious flaws. In particular, it may overstate the problem of high housing costs in the upper end of the market (someone who earns $200,000 can choose to pay a huge amount for housing and still afford all of life’s other necessities), while understating the burden on low-income families who need a much greater percentage of their smaller incomes to buy food, clothing, and so on. Nor does the report’s metric touch on other location-based costs, like transportation, which adds meaningful and important context as the geography of housing demand, poverty, jobs, and transit service changes.

The JCHS/Enterprise report is a valuable reminder that housing costs remain a serious problem in many parts of the country. But we shouldn’t just take it as a general alarm: it contains concrete lessons for those working to improve housing policy—especially the need to grow the rental housing supply where there is demand and reform zoning laws to allow the full range of housing options to accommodate single people in all neighborhoods—that, along with more aggressive subsidized housing programs, offer at least the outlines of a path forward.