The Impact of Urban Development on Housing Affordability: A Case Study

A note on this example

Everything below is a hypothetical built to illustrate how the arithmetic of affordability works. It does not describe a real city, project or result, and every number is invented for teaching. Real districts differ in ways that matter, so treat this as a thinking tool, not a prediction.

The starting point

Imagine a district called Eastgate, a fictional area with 1,000 existing apartments, mostly older buildings. Assume:

• The typical household income in the district is $50,000 a year.
• Existing apartments rent for about $1,100 a month.
• The affordability rule of thumb is 30 percent of income spent on housing.

At $50,000 a year, 30 percent is $15,000 a year, or $1,250 a month. A rent of $1,100 sits under that line, so the typical household in the fictional district is not cost-burdened under this rule. Which household incomes can afford a $1,100 rent? Multiply by 12 to get $13,200 a year, then divide by 0.30 to get $44,000. So any household earning at least $44,000 would pay no more than 30 percent of income there. Households below that would be stretched.

The proposed development

The district approves a project that adds 250 homes:

• 200 market-rate units renting at $2,000 a month.
• 50 subsidized units reserved for households earning up to 60 percent of the area’s typical income, with rents capped at 30 percent of that level.

Check the numbers:

• 60 percent of $50,000 is $30,000 a year. Thirty percent of that is $9,000 a year, or $750 a month. So the subsidized rent cap is $750.
• A $2,000 market-rate rent is $24,000 a year. Dividing by 0.30 gives $80,000. A household needs roughly $80,000 a year to rent a market-rate unit without exceeding the 30 percent rule.

After construction, the district has 1,250 homes. Of these, 1,000 are older units (80 percent), 200 are new market-rate units (16 percent) and 50 are subsidized (4 percent). The shares add to 100 percent.

What changes, and what does not

Supply rose by 25 percent. Going from 1,000 to 1,250 homes is an increase of 250, which is 25 percent of the original 1,000.

Most new units target higher incomes. Few households at the district’s typical $50,000 income could afford $2,000 a month under the rule of thumb. The new market-rate units therefore primarily serve households earning around $80,000 or more, who might otherwise have looked for homes in the older stock or elsewhere in the region.

The subsidized units serve a lower tier. Eligible households earning up to $30,000 pay no more than $750, so these homes are within reach for households that the market-rate units are not. But there are only 50, and in a real place there could be far more eligible households than units, so allocation by waiting list or lottery matters.

Three ways the story could unfold

Because this is a hypothetical, consider several possible outcomes, none of them guaranteed.

1. Relief outward. If the 200 market-rate units attract higher-income newcomers who would otherwise have competed for older apartments, pressure on the $1,100 rents may ease or at least not grow. Proponents of supply expansion point to this effect.
2. New demand. If the new buildings make the district more attractive, bringing a new store, a safer-feeling street or a stronger reputation, demand might rise faster than supply and older rents might climb anyway. Some households could find the $1,100 rent drifting toward $1,250 or beyond.
3. Mixed. Some blocks see rent relief and others see pressure, depending on how close they are to the new buildings, the condition of the older stock and the regional market.

Which scenario dominates is an empirical question, and the research on small-area effects is mixed. This is why the broader picture of development and housing costs stresses time frame and scale.

Reading the share of subsidized units

Fifty out of 250 new homes is 20 percent of the project. But fifty out of the district’s 1,250 total is 4 percent. Both numbers are honest and answer different questions: how inclusive is the project, and how much does it change the district overall? Be wary of figures that quote only the more flattering one.

What the hypothetical suggests

• A project can add supply and still leave a gap at the income level of the typical household. Here, neither new category was priced for $50,000 earners.
• Subsidy changes who is served at the bottom, but quantity matters as much as price. Affordable units that number only a few dozen reach few families.
• Policy design shapes outcomes. If the district had required a higher share of lower-priced units to create mixed-income housing, or paired the project with tenant protections for existing residents, the picture would differ. Those choices have costs, such as reduced project profit, that can affect whether the project gets built at all.
• Public benefits may be traded for height. A city could grant density bonuses in exchange for more subsidized homes, but that works only if the project’s numbers still hold up in its development pro forma.
• Local services matter. Adding 250 homes raises the question of infrastructure capacity for water, sewers and roads, and the fees used to pay for it can raise the cost of each unit.
• Tracking results requires data. A city would compare rents, vacancy and displacement before and after, not simply count new units.

Questions to carry into a real case

When you meet a real project described as boosting affordability, check the unit counts, the rent levels, the income thresholds and the time frame. Then compare the rents to local incomes the way this example does. The arithmetic is simple, but it often reveals who a project is, and is not, meant to serve.