WHAT THE AUTHORS EXAMINED

The study measured:

• Total housing units over time

• Units affordable at different income levels (ELI, VLI, LI, MI, >Median)

• Rent levels

• Address counts

• Permit activity

• Local zoning reform data

The authors compared cities that:

• Increased density allowances (upzoning)

• Decreased density (downzoning)

• Stayed the same (control group)

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KEY FINDING #1 — Upzoning Increases Supply by Less Than 1%

The most shocking data point in the study:

 

Upzoning led to a 0.8% increase in total housing units — spread over 9+ years.

A 0.8% increase is far too small to affect prices or affordability.

 

This single statistic dismantles Sightline’s claim that “if you just let people build more, rents will fall.”

 

KEY FINDING #2 —Upzoning Creates LUXURY Units, Not Affordable Units

The authors found:

• Almost all new units were priced for above-median income households

• No statistically significant increase in units affordable to:

  • Extremely low-income (ELI)

  • Very low-income (VLI)

  • Low-income (LI)

  • Middle-income (MI)

Their exact wording:

 

“We find no statistically significant evidence that lower-cost units became available following upzoning.”

This destroys the “filtering works everywhere” talking point.

 

KEY FINDING #3 — Upzoning Does NOT Reduce Rents

The study tested rent levels specifically and found:

 

“No significant effects on rent levels.”

This directly contradicts Sightline’s video.

If increased density lowered rents, it would show up here.

It does not

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KEY FINDING #4 — Upzoning Raises Nearby Rents Through Amenity Effects

New dense buildings create:

• New amenities

• Higher-income residents

• Upgraded infrastructure

• Higher land desirability

The authors found that in many cities:

 

These “amenity effects” outweigh the small supply increase — causing rents to stay flat or rise.

This explains the pattern seen in Bellingham:

• New market-rate apartments →

• Higher assessments →

• Higher land values →

• Higher taxes →

• Higher rents for everyone nearby

Density raises the baseline cost structure.

KEY FINDING #5 — Downzoning (Restricting Density) Increases Rents

When cities reduced allowed density:

• Rents rose

• Fewer middle-income units were available

This means Bellingham’s refusal to annex UGAs — thereby restricting available land — is functionally a downzoning of the entire city.

Exactly what the study warns against.

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WHY THIS STUDY MATTERS FOR BELLINGHAM

0 of 15 UGAs annexed → land scarcity

✔ Population +30% → demand surge

✔ Upzoning → same pattern as study (luxury units only)

✔ Rents → rising

✔ Affordable units → disappearing

✔ City fees → skyrocketing with dense construction

 

Bellingham perfectly matches the national pattern documented by this study.

Upzoning in a land-constrained, high-fee, high-cost, low-supply-expansion city:

👉 Creates expensive units
👉 Raises land values
👉 Helps city budgets
👉 Does nothing for affordability
👉 Hurts renters
👉 Rewards government inefficiency

This is why Bellingham is pushing density so aggressively.

 

Not because it works for affordability — but because it works for revenue.