Modest Densification

Modest Densification & Housing Access

Housing Affordability Institute’s Modest Densification series highlights how zoning modernization through modest densification can increase housing inventory, affordability, and access.  

Housing access, the ability of individuals and families to find affordable and suitable housing, is a growing public policy concern. However, numerous barriers, including restrictive zoning regulations, have hindered housing access for many, disproportionality impacting communities of color. Zoning reform via modest densification offers a powerful solution to this challenge, as it can enhance housing access by supplying a diverse set of housing options.

Modest densification is a subtle increase in housing density ‘by right’ over current zoning controls which dictate density via ordinance or the Planned Unit Development (PUD) process. On the same amount of land, more housing units can be built. Whether is it a duplex or twin home, a home with an accessory dwelling unit, or a series of townhomes, the result is the same: more housing.

Housing Access & Housing Density

More than simply adding new housing, modest densification can be a way to open housing access opportunities to a diverse population. According to research by Salim Furth of the Mercatus Center and MaryJo Webster of the Star Tribune, increased density can increase racial diversity in a community.

Looking at data in the Twin Cities, home to the largest housing equity gap in the nation, missing middle housing and modestly dense developments were shown to have a more diverse makeup than straight-zoned by-right developments:

In the Twin Cities metro, which has unique ethnic demographics, we find strong, robust associations between zoning and racial residential patterns. An area zoned for multifamily housing has, on average, 21 percentage points more non-White residents than an identically situated single-family zone.

A district that allows fourplexes, duplexes, townhouses, or mobile homes in addition to detached houses has, on average, 14 percentage points more non-White residents than a single-family district, although detached single-family houses remain the most common dwelling type in middle housing zones. Hispanic and mixed-race people appear especially likely to live in middle housing zones.”

Furth, Salim and Webster, MaryJo. “Single-Family Zoning and Race: Evidence from the Twin Cities.” Mercatus Center. Oct. 11, 2022.

Zoning modernization, they noted, would help to address racial disparities in housing access.

Modest Densification & Ending Exclusionary Zoning

The alternative to by-right flexibility is a zoning variance via planned unit development (PUD). Employment of a PUD opens the project applicant to a “give-and-take” negotiation with local officials in which housing costs are often increased in exchange for increased density. In their research, Furth and Webster examined how the PUD process impacts affordability and access, finding that it has an exclusionary effect.

By creating more flexibility in by-right housing options, modest densification can prevent municipalities from enacting exclusionary zoning added into the PUD negotiation. This includes imposition of aesthetic mandates, design reviews, or increased fee exactions or land dedications, all of which increase housing costs.

Housing Options Reflecting Changing Demographics

In many residential areas, single-family detached housing is the norm. In greenfield development areas, where new housing is being built and new housing patterns established, the zoning preference is for large lots and larger homes, much like it did in the 1980s and 1990s:

  • Marriage Rates: In 1990, 39.28% of men and 43.11% of women were unmarried. By 2022, those figures have increased to 48.33% of men and 50.13% of women. The share of unmarried Americans includes those never married, widowed, and divorced. ~
  • Delayed Marriage: Americans have delayed marriage more than a year over the three decades. In 2022, the average age of a first marriage in America was 30.1 years for men and 28.2 for women, compared to 26.1 for men in 1990 and 23.9 for women.  ~
  • Single-Person Households Increasing: With growth in single-person households and delays in marriage, there is also an increase in single-person households. In 2022, the number of single-person households was 29% up from 25% in 1990.
  • Multi-Generational Households Growing. After bottoming out in 1980 at 12.1%, the share of Americans living in a multigenerational household is growing and is now at 18%. (Pew Research Center, The demographics of multigenerational households)

The reality is that America is changing, and our housing options are no longer reflective of the demographics of today. Suburban zoning controls are failing to keep pace with demographic changes and the proliferation of modest densification can increase the number of housing options available by right to a changing population.


Modest densification is a transformative tool for expanding housing access and creating more inclusive communities. By promoting inclusivity, affordability, accessibility, and diversity in housing options, zoning reform breaks down barriers that have historically restricted housing access for marginalized and underserved populations. Policymakers and community leaders must recognize the potential of zoning reform to address the housing access challenge and work together to implement inclusive and equitable zoning policies.

~ U.S. Census Bureau