Portland: Residential Infill Project (RIP)

Portland's Residential Infill Project, almost always shortened to RIP, did not start in a state capitol or a developer boardroom. It started locally, with residents and housing advocates pushing the city to let more homes be built on ordinary residential lots. The Portland City Council approved the general concept in 2016, and the project then moved through years of public hearings and revisions before it became law. By September 2018, the city's planning commission had already held packed hearings, where supporters slightly outnumbered opponents.

The timing matters for British Columbia readers, because it shows that Portland was already well down this road before its state forced the issue. Oregon's statewide middle-housing law, House Bill 2001, passed in 2019. Portland's RIP went well beyond the requirements of that state law, which legalized middle housing but stopped short of allowing it on any lot. In other words, the city volunteered for a deeper reform than the state required. The Seattle-based research group Sightline Institute called RIP the best low-density zoning reform in US history. That is a strong claim, and the production numbers that came later, covered further down this page, are the main reason it has held up.

Before RIP, most residential land in Portland allowed only a single house on a lot, with a duplex permitted on some corner lots. RIP rewrote that. The Portland City Council voted 3-1 to adopt the project on August 12, 2020, with most of the changes taking effect on August 1, 2021. The core change: across most lots that had been limited to a single house, the new rules permit duplexes, triplexes and fourplexes, as long as each building follows new limits on size and scale.

RIP was passed in two parts. Part 1 is the August 2020 reform described above. Part 2 came later: the City Council voted unanimously to adopt the Residential Infill Project – Part 2 on June 1, 2022, with the ordinance taking effect on June 30, 2022. Part 2 extended the rules to the rest of Portland's residential zones, including larger lots in outlying areas, and added standards for attached houses and cottage clusters, which are small groups of compact homes arranged around shared open space. Together, the two parts cover the residential neighbourhoods that make up 75% of the city's land where housing is allowed.

The cleverest part of RIP is how it sizes buildings. Instead of capping every lot at one fixed building size no matter how many homes go inside, Portland tied the allowed floor area to the number of units. The more homes you put on the lot, the more total floor area you are allowed. A duplex in Portland can be up to three-fifths the square footage of its lot, and triplexes and fourplexes up to 0.7 times the lot size. Floor area ratio, often shortened to FAR or FSR, simply means the total floor space of a building divided by the size of the lot it sits on.

That design choice is the difference between a reform that works on paper and one that gets built. Sightline contrasted Portland's approach with Minneapolis, which legalized triplexes in 2018 but held every building to a uniform 50% limit regardless of unit count. Under a flat cap, splitting a building into three or four homes just means three or four smaller, tighter units inside the same envelope, which often does not pencil out for a builder. By giving extra floor area to projects that add more homes, Portland made the triplex and fourplex the financially sensible choice rather than a penalty. RIP also removed parking requirements: the reform made home driveways optional citywide for the first time since 1973 and lifted parking mandates from most residential land, which removes a major cost and space burden from small infill projects.

RIP includes an incentive aimed squarely at below-market housing. On a standard lot the cap is four homes, but a builder can go higher by committing to affordability. Under the deeper-affordability option, a site can hold up to 6 units when half of those units are affordable to households earning up to 60% of the median family income. In plain terms, if you agree to rent or sell at least half the homes at regulated, lower prices to households of modest means, the city lets you build two extra homes beyond the normal limit.

This is a trade the city offers rather than a mandate it imposes. A builder is free to stick with a market-rate fourplex, or to reach for six homes by accepting the affordability conditions on half of them. Sightline described the same provision as four to six homes on any lot if at least half are available to low-income Portlanders at regulated, affordable prices. The point of the bonus is to use the value of extra density as the carrot that pays for the affordable homes, rather than relying on public subsidy alone.

This is the part that turns RIP from a nice idea into a case study other cities cite. In February 2025 the City of Portland published a progress report, and the numbers are unusually clear. Between August 1, 2021 and June 30, 2024, the city permitted over 1,400 accessory dwelling unit and middle-housing units in single-dwelling zones. More striking is the share of the city's total housing that those neighbourhoods now produce. Historically, single-dwelling residential zones supplied only 10 to 20% of the city's total housing production. That figure rose to 23% in 2023 and then jumped to 43% in the first half of 2024. Neighbourhoods that used to add almost nothing to the housing supply are now responsible for close to half of it.

The price gap is just as important. In 2024, the average new market-rate middle-housing unit cost about $460,000, compared with about $916,000 for a new detached house in the same single-dwelling zones. The report translated that into household income. To afford a new triplex or fourplex unit, a three-person household needed roughly $116,000 a year, versus about $233,000 a year for a new detached house. The middle-housing path put a brand-new home within reach of a household earning half as much. That is the whole argument for this kind of reform, expressed in dollars rather than slogans.

Oregon's House Bill 2001 set a statewide minimum: large cities had to allow middle housing. But a statewide minimum is a floor, not a ceiling, and floors tend to be cautious. Portland chose to go further on the details that decide whether anything gets built. The state law stopped short of allowing middle housing on any lot; RIP did not. Portland paired that broad permission with the unit-based floor-area rule, the affordability bonus, and the removal of parking mandates.

Those three choices are why the permits actually flowed. A reform that legalizes a fourplex but caps it at the size of a single house, demands two or three parking stalls, and offers no path to extra homes will produce a trickle. Portland removed each of those choke points. The lesson for any jurisdiction copying the model is that legalizing a housing type is necessary but not sufficient. The size limits, the parking rules, and the financial incentives decide whether the type is buildable. Portland treated those secondary rules as the main event, and the jump from 10 to 20% of production up to 43% is the result.

RIP is not a finished story, and honest analysis should say so. The price figures describe new construction in 2024, after several years of high interest rates and elevated building costs, so a $460,000 middle-housing unit is cheaper than a new detached house but is still not low-income housing on its own. The deeper-affordability bonus is the part of RIP that produces genuinely below-market homes, and it depends on builders choosing to use it; most market-rate fourplexes do not. The report's 1,400-plus units over nearly three years is a strong result for a reform of this kind, but it is modest against the scale of a regional housing shortage, and it arrived during a period when overall construction was constrained by financing costs.

There is also a measurement caution. The 43% share is from the first half of 2024, a single half-year, and partly reflects a slowdown in large apartment construction as much as a surge in infill. A share can rise either because the numerator grows or because the rest of the market shrinks. The unit counts and the price comparison are the more durable evidence; the share figure is best read as a signal of direction rather than a permanent new normal. None of this undercuts the core finding, but it keeps the claim honest: RIP measurably shifted where and what Portland builds, without by itself solving affordability.

British Columbia arrived at a similar destination by a different route. The province passed Bill 44, the Small-Scale Multi-Unit Housing legislation, in 2023, and required municipalities with populations over 5,000 to rezone for three to six units on most single-family and duplex lots by June 30, 2024. Where Portland's reform was homegrown and the city pushed past its state's floor, BC's was top-down, with the province compelling cities to act. The end state is comparable: small multiplexes are now permitted by right across formerly single-family neighbourhoods on both sides of the border.

The instructive difference is in how generous the size rules are. Portland gives a triplex or fourplex a floor area ratio of up to 0.7 and removed parking mandates from most residential land. Vancouver's multiplex rules, set out in its R1-1 zone that took effect in October 2023, allow up to six units, but start from a base floor space ratio of only 0.70, reaching 1.0 only when a project meets extra conditions such as securing all units as rental or providing a below-market homeownership unit. Vancouver also steers multiplexes toward an average unit size of roughly 1,000 square feet with ground-oriented design. Those are tighter design strings than Portland attaches. The takeaway for BC is the same one Portland's own data teaches: legalizing the multiplex is the easy half. Whether the building actually gets built turns on the floor-area allowance, the parking rules, and the design conditions, and those are exactly the levers where Vancouver is more cautious than Portland. Portland's production record is the best available evidence that the generous version of these rules is the one that delivers homes.