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New study shows promising housing production results from the Residential Infill Project (RIP)

News Article
Street view photo showing recent middle housing construction in Portland
A year after new rules governing single-dwelling zones went into effect, middle housing and accessory dwelling unit (ADU) production have increased dramatically.

One year after City Council passed the Residential Infill Project (RIP) , the zoning code changes went into effect on Aug. 1, 2021. This project established new limits on building size, created new allowances for middle housing types, and expanded allowances for accessory dwelling units in Portland’s single-dwelling zones (R2.5, R5, and R7).

To evaluate the development outcomes from the first year of implementation, the Bureau of Planning and Sustainability (BPS) contracted Cascadia Partners, LLC to conduct an analysis of the first year of housing development in Portland’s residential zones since RIP went into effect.

Read the full report

Read the executive summary

The sample size for the study was small, 646 units total, and included development activity during the COVID-19 pandemic, which was not a typical development cycle. Nevertheless, the initial results are impressive.

RIP year-one results

In the first year of RIP implementation, 271 units of middle housing (duplexes, triplexes, fourplexes and sixplexes) were permitted in the R2.5, R5 and R7 single-dwelling zones, compared to 102 new single-dwelling houses. In other words, excluding ADUs, 73% of units permitted in these zones were middle housing. Fourplexes made up the largest share of middle housing units permitted (76%), followed by duplexes at 13%, triplexes at 10% and sixplex units at 1%.

Chart from the RIP Year-One report showing permit activity by housing type in the single-dwelling zones.

Furthermore, these 271 permitted middle housing units will be built on just 81 lots, which is more than double the rate for single-dwelling construction. 

New units built near centers and corridors with lots of amenities

While the Planning and Sustainability Commission applied the new housing allowances in residential neighborhoods throughout the city, more new middle housing is being built near the city’s “centers and corridors” ― places where jobs, services and amenities are conveniently located and where Portland’s 2035 Comprehensive Plan anticipates most of the city’s growth to occur. Eighty-six percent of middle housing units were located within a quarter mile of centers and corridors, compared to 60% of single houses. And neighborhoods that were identified as “at risk” for displacement (i.e., Montavilla, Lents, Brentwood-Darlington) did not see significant middle housing development.

Map from the RIP Year-One Report showing the location of middle housing permits overlaid on the City's designated centers and corridors.
Download the full PDF version of this map

Greater variety of housing choices offers more opportunities

Exterior street view photo of recent middle housing construction
Recent example of a detached accessory dwelling unit (ADU).

ADUs continue to be an important part of the housing mix in the single-dwelling zones, matching middle housing unit production at 42% each of the total, with single houses making up the remaining 16%. The project expanded allowances for ADUs by enabling homes to have two ADUs, duplexes to have one ADU, and ADU basement conversions to exceed prior size limits, which enabled 40% more ADUs to be permitted. Due to their size limits, ADUs are typically studio or one-bedroom units, which mostly serve smaller households.

Conversely, middle housing provides more options for growing or multi-generational households; more than 99% of permitted units had two or more bedrooms, and 24% of the units had three or more bedrooms. So, finding a home that is well suited for differently sized households should become easier as this diversity in housing types continues.

Pie chart from the RIP Year One report showing the percent of housing units permitted in single-dwelling units

Impact of size limits

New unit size limits imposed by RIP were also an important part of the success story. Cascadia Partners evaluated homes built in the four years before the new limits took effect and found that homes built in excess of the new maximum floor area ratios, one-third to one-half of all homes, sold for an average of $117,000 more than homes at or below those limits.

Bar chart from the RIP Year One report showing average close price of middle housing units both over and under FAR limits
Detached single-family homes over the current FAR limit sold for substantially more than those below the limit.

New homes built in the first year after RIP went into effect were generally between 2,100 and 2,400 square feet in floor area. Triplex and fourplex units tended to average between 950 and 1,300 square feet each, and duplex units were between 1,300 and 1,600 square feet.

Key takeaways

RIP was informed by thousands of public comments and countless interactions between stakeholders, staff, Planning and Sustainability Commissioners, and City Council over the course of several years. This comprehensive and inclusive process resulted in several significant changes to shape and refine the proposal along the way, which has ultimately led to this promising renaissance in neighborhood housing.

Summarizing a few of the study’s key takeaways:

  1. Excluding ADUs, middle housing accounts for 73% of the 373 units permitted in the first year.
  2. Fourplex units comprised 76% of all middle housing units in the R2.5, R5 and R7 zones.
  3. Middle housing is a more efficient use of land than houses, achieving 3.4 units versus 1.2 units per lot.
  4. More than 99% of middle housing units had two or more bedrooms, and 24% of units had three or more bedrooms, offering more choices and flexibility for growing or multi-generational households.
  5. ADUs continue to be an important part of the housing mix, equaling middle housing unit production.
  6. Comparing newer homes that met RIP's adopted floor area size limitations to larger homes built before RIP, these smaller homes were $117,000 less expensive, on average.