Rents have been on the rise nationally for several years, but in some cities the rate of appreciation has been particularly high. The reasons are varied, but the law of supply and demand — a shortage of inventory and a surplus of renters — is usually in play. More and more people are renting, either by choice, because they enjoy the lifestyle and flexibility, or by necessity, because homeownership is out of reach.

To accommodate this increasing population of renters, new multifamily communities are cropping up all over — so inventory shouldn’t be so tight, and rents shouldn’t keep rising — right? That seems to be the trend in some areas, but there’s another, less obvious factor influencing the market: land-use regulations. Recent Zillow research found that between 2011 and 2016, rents in cities with the most restrictive regulations increased nearly three times as much compared to cities with the least restrictive regulations. Renters might be feeling the pinch in these areas, but developers and management companies are impacted as well.

Despite the demand, it can be harder to build

When zoning rules and building codes are stricter, constructing new apartment buildings can prove more difficult — or at least take longer. Often, lengthy approval processes, extra oversight and additional inspections must be factored into the timeline. In the meantime, rental demand keeps rising, but because the inventory isn’t coming online fast enough to accommodate it, rent growth accelerates.

San Francisco is a notable example: With the highest median rent in the U.S. and a steady stream of new residents, it should be ripe for a building boom. But, with highly restrictive land-use regulations — plus the geographic limitations imposed by the coastline — construction is challenging, and the Bay Area’s supply cannot keep up with demand.

The land-use issue is complex; some consider restrictions to be hostile to development and a barrier to affordable housing, while others believe the regulations are critical to maintaining environmental integrity and quality of life. Regardless of which stance you take, the data shows a clear correlation between high regulation, low inventory and high rents.

More renters are cozying up to the idea of shared living

The increasing number of millennials living with their parents has been the buzz in housing news, but plenty of young professionals do opt to leave the nest. When new inventory is slow to open up, however, those with visions of starting out on their own may not really be “on their own”; renters who want to stay within their desired area might find themselves bunking up with a roommate, and that’s especially true where land-use regulations are strict. Between 2011 and 2014, the increase in the number of adults per household was nearly double in cities with the most restrictive regulations vs. those with the fewest regulations.

Apartment communities with additional living and socializing areas, such as outdoor dining and green spaces or indoor lounges and coffee bars, can expand the concept of “home” and offer greater appeal to renters who are sharing their primary living space.

Young or old, everyone’s doing it

It’s not just kids straight out of high school or college who are living with roommates to stretch their housing dollars. The “doubling up” phenomenon is spanning all generations. Multigenerational households are on the rise, and 32 percent of adults between the ages of 23 and 65 are now in doubled-up households (compare that to 25 percent in 2000). Whether renters are looking for companionship or just need help with the bills, they’re more likely to be living with roommates in cities where inventory is limited and regulations are restrictive.

If your area can’t (or won’t) easily accommodate more units, your communities are likely to see greater rent appreciation and more renters of all ages adding roommates to spread out the cost.