The shortage comes down to cost, zoning rules, and what developers can actually afford to build
Affordable housing is scarce because building it costs nearly as much as building market-rate housing, but you can charge far less rent. A developer who builds a 100-unit apartment complex spends the same money on land, labor, permits, and materials whether units rent for $800 or $1,800 a month. When the math doesn't work, developers build for higher-income renters instead. Add zoning laws that ban multi-unit buildings in most residential neighborhoods, and you get a market where supply can't keep up with demand — especially at the bottom end of the price range.
The gap between construction cost and what low-income renters can afford is the core problem. A renter earning $25,000 a year can afford roughly $625 a month in rent. A new apartment in most markets costs $1,200 to $1,500 a month to operate and profit from. That $575-to-$875 gap doesn't close on its own. Without subsidy, tax breaks, or a developer willing to accept lower returns, the unit doesn't get built.
Key Takeaways
- Building costs are the same whether a unit rents for $800 or $1,800, so developers choose the higher rent unless subsidies or tax incentives make affordable units profitable.
- Zoning rules in most neighborhoods prohibit apartment buildings, duplexes, and other multi-unit housing, which keeps supply artificially low across all price points.
- Land prices in desirable areas with jobs and transit are so high that even subsidized projects struggle to pencil out financially.
- Affordable units that do get built often come with deed restrictions that last 30 to 50 years, after which landlords can convert them to market-rate housing.
Construction costs don't change based on who lives there
A contractor charges the same hourly rate whether they're framing a unit for a low-income tenant or a high-income one. Concrete, drywall, electrical wire, and labor all cost what they cost. A developer's financing, insurance, and profit margin don't shrink because the tenant earns less. This is why affordable housing requires outside money to work.
In most cases, that money comes from government subsidies, tax credits, or philanthropic funding. The federal Low-Income Housing Tax Credit (LIHTC) is the largest tool — it lets investors reduce their federal taxes in exchange for funding affordable projects. Some cities use inclusionary zoning, which requires new market-rate buildings to include a percentage of affordable units, or offers density bonuses (permission to build taller or larger) in exchange. Without these mechanisms, a developer has no reason to build at below-market rates.
Even with subsidies, the math is tight. A project that costs $15 million to build and generates $800,000 a year in rent needs tax credits, grants, or below-market financing to break even. If any of those funding sources disappear or shrink, the project stalls.
Zoning laws prevent the housing types that would naturally be cheaper
Most American neighborhoods are zoned for single-family homes only. This rule, called single-family zoning, covers roughly 75 percent of residential land in many cities. It bans duplexes, triplexes, apartment buildings, and accessory dwelling units — the housing types that historically provided affordable options because they spread costs across more units per lot.
When you can only build one house per lot, land cost per unit is high. A $500,000 lot with one house on it costs $500,000 per unit. The same lot with a four-unit building costs $125,000 per unit. That difference flows directly into rent. Single-family zoning also limits total housing supply, which pushes prices up across the board — including for renters who can't afford market rates.
Some cities have begun allowing duplexes or small apartment buildings in single-family zones, but this change is recent and incomplete. Most neighborhoods still prohibit multi-unit housing, which means affordable options can only be built on the small fraction of land zoned for apartments or mixed-use development. That scarcity drives up land prices in those zones, making affordable projects harder to finance.
Land in places with jobs and transit is too expensive
Affordable housing is most needed near employment centers, public transportation, and services — but those are exactly the places where land costs the most. A lot in downtown or near a transit hub might cost $2 million per acre. A lot in a distant suburb might cost $200,000 per acre. The same affordable housing project is ten times harder to finance in the location where it's most useful.
Developers and nonprofits sometimes solve this by building farther out, where land is cheaper. But that creates a different problem: residents spend more on transportation, work longer commutes, and may have less access to jobs, schools, and services. A unit that costs $700 a month in rent but requires a $300 monthly car payment and two hours of commuting is not actually affordable.
Some cities have tried to address this by acquiring land in expensive areas and holding it for affordable projects, or by allowing developers to build taller buildings in exchange for including affordable units. These tools work, but they require sustained public funding and political will.
Deed restrictions limit how long units stay affordable
Most affordable housing built with public money comes with a deed restriction — a legal requirement that the unit remain affordable for a set period, usually 30 to 50 years. After that period ends, the owner can convert the unit to market-rate housing or sell the building to someone who will. This means the affordable stock is constantly shrinking as older restrictions expire.
A unit built in 1995 with a 30-year restriction becomes market-rate in 2025. The owner has no incentive to keep it affordable once the restriction ends and can charge whatever the market will bear. Cities and nonprofits sometimes try to renew restrictions or purchase buildings before they convert, but they don't have enough funding to save all of them.
This creates a treadmill: cities must constantly build new affordable units just to replace the ones aging out of affordability. Without a growing pipeline of new construction, the total stock shrinks.
Financing is harder for affordable projects than market-rate ones
Banks and investors prefer market-rate housing because the returns are higher and more predictable. An affordable project with a 4 percent return on investment is riskier and less attractive than a market-rate project with an 8 percent return. Lenders charge higher interest rates for affordable projects, which makes them more expensive to build and operate.
Affordable projects also depend on multiple funding sources — tax credits, grants, below-market loans, and sometimes donations. Assembling that funding takes longer and requires informed. A developer building market-rate housing can often get a single construction loan and move forward. An affordable project might need five different funding sources, each with its own timeline and requirements.
When interest rates rise or tax credit demand falls, affordable projects are the first to stall. Market-rate projects can absorb higher costs by raising rents. Affordable projects can't, so they become financially unfeasible.
Population growth and migration outpace new construction
In many regions, people are moving in faster than housing is being built — at any price point. When demand outpaces supply, prices rise. Low-income renters get pushed out first because they have the least ability to pay more. Even if a city builds some new affordable units, if overall housing supply is tight, market-rate rents will rise, and low-income residents will still be squeezed.
Some of this is demographic: young adults are moving to cities for work, and older adults are living longer. Some is migration: people relocate from high-cost regions to lower-cost ones, raising prices in the destination. Some is economic: remote work has made it possible for higher-income people to move to cheaper areas, bidding up prices there too.
Building enough housing to keep up with this demand requires sustained construction at a scale most cities haven't achieved. It also requires building across all price points, not just affordable units, because the overall shortage pushes everyone's costs up.
Frequently Asked Questions
Why don't developers just accept lower profits on affordable housing?
Because investors and lenders expect a competitive return on their money. A developer who accepts a 2 percent return on an affordable project could earn 8 percent building market-rate housing. Over time, that difference compounds. Without subsidy to close the gap, developers have no financial reason to build affordable units.
Could building more housing in general help affordable housing?
Yes, but only if it includes affordable units or is built at a scale that increases overall supply enough to ease pressure on lower-income renters. Building only luxury apartments in a tight market doesn't help people earning $25,000 a year. Building a mix of housing types and prices, across many neighborhoods, does reduce pressure on the entire market.
What happens to affordable units when deed restrictions expire?
The owner can convert them to market-rate housing or sell the building. There's no automatic renewal. Cities sometimes purchase buildings before restrictions expire to keep them affordable, but they don't have funding to save all of them. This is why the affordable stock shrinks over time without new construction.
Is zoning the main reason for the shortage?
Zoning is a major factor because it limits where housing can be built and what types are allowed. But it's not the only one. Even in areas where zoning allows apartments, construction costs and land prices still make affordable units difficult to finance without subsidy. Changing zoning helps, but it's not a complete solution on its own.
Why is affordable housing built so far from jobs?
Because land is cheaper in distant areas, which makes projects financially feasible. But this trade-off means residents spend more on transportation and have longer commutes. Building affordable housing near jobs requires either cheaper land (which is rare in those areas) or public funding to cover the difference.