Can you build a fourplex in Seattle? Yes, on every Neighborhood Residential lot.

Yes. Every Neighborhood Residential (NR) lot in Seattle now allows at least 4 homes, and that rule became permanent on January 21, 2026 under the One Seattle Plan. The exact base is "the greater of 1 unit per 1,250 sq ft, or 4 units," so most standard lots land at 4. Any accessory dwelling units you build count toward that total. If your lot is near frequent transit or you make some homes affordable, the ceiling goes higher than four.

It depends on where the lot sits and whether you include affordable homes. The base is 4 homes anywhere in the NR zone. Within a quarter-mile of a major transit stop, or if at least 2 homes are affordable, the base rises to 6. A stacked-flats building on a lot of 6,000 sq ft or more near major transit can reach 9. And if at least half the homes are affordable, a 5,000 sq ft lot near transit can reach 12, the highest the NR zone allows.

The One Seattle Plan is Seattle's update to its Comprehensive Plan and the zoning that carries it out. It is how the city met the requirements of Washington's state middle-housing law, HB 1110. The permanent version was adopted by the City Council on December 16, 2025 through two bills: Council Bill 120985 for the Comprehensive Plan and Council Bill 120993 for the Neighborhood Residential zoning. The zoning took effect on January 21, 2026.

Effectively, yes. The One Seattle Plan is the first full rewrite of the Neighborhood Residential zone since 1982, and it means every NR lot now allows at least 4 homes rather than one house. The city did not ban detached houses. You can still build a single home if you want. But the old "one house only" rule is gone across the Neighborhood Residential zone, which covers most of Seattle's residential land.

These are the two ways to build above the 4-to-6 base. The stacked-flats bonus lets a lot of 6,000 sq ft or more within a quarter-mile of major transit hold up to 9 homes, at a floor-area ratio of 1.8. The low-income bonus goes further: if at least half the homes are affordable (60% of area median income for rentals, or 80% for ownership) a 5,000 sq ft lot near transit can reach 12 homes, at 1.8 floor-area ratio and up to 4 stories. Both bonuses are tied to being near major transit.

Often no. No off-street parking is required within a half-mile walk of light rail, commuter rail, or bus rapid transit. No parking is required for any home that is 1,200 sq ft or smaller, wherever it sits. ADUs never require parking. Outside those cases, the rule is 1 parking space for every 2 homes. Because so much of Seattle sits near frequent transit or involves smaller units, many projects owe no parking at all.

The base height limit is 32 feet, which rises to 42 feet if you keep existing trees on the lot. Lot coverage is capped at 50%, so at least half the lot stays open. Floor-area ratio starts at 0.6 and rises to as much as 1.6 by density, and the two transit bonuses reach 1.8. These envelope rules, height, coverage, and floor area, usually decide what actually fits on a given lot, more than the unit count alone.

Seattle rewrote its ADU rules in 2019, and they are some of the most flexible in the United States. You can build up to 2 ADUs per lot: either 2 attached units, or 1 attached plus 1 detached backyard cottage (a DADU). There is no owner-occupancy requirement, so you do not have to live on site to rent them out, and there is no parking requirement for an ADU. Detached backyard cottages are capped at 1,000 sq ft. Under the 2026 rules, ADUs also count toward your total unit limit.

It is large and still growing. ADU permits rose from 482 in 2020 to 987 in 2023, roughly double in three years. ADUs now outnumber new single-family-home permits by about 2 to 1. And about 70% of new single-family permits now include an ADU, so most people building a house are adding a second home at the same time. The 2019 rules that removed the owner-occupancy and parking requirements are widely credited for that jump.

Yes. Interim rules (Council Bill 120969) took effect on June 30, 2025 to meet the state deadline, and the permanent rules took effect on January 21, 2026 after the Council adopted them on December 16, 2025. As of July 2026 the permanent Neighborhood Residential zoning is the law that applies. This is not a proposal or a pilot. It is the current, adopted zoning across the NR zone.

There is no published build count yet, and it would be misleading to give one. The permanent rules only took effect on January 21, 2026, so the city has not had time to accumulate meaningful permit or completion data under them. The honest answer is that the outcome is still unknown. What we can measure is the ADU trend, which has been strong for years, and the fact that every NR lot now legally allows at least 4 homes.

Not below 5,000 sq ft. Under the current rules, new lots smaller than 5,000 sq ft cannot be created. Separate lot-splitting legislation was expected in 2026 to allow smaller lots, but as of July 2026 it is not confirmed that it passed, so do not count on it. For now, the way to add homes is to build more units on your existing lot under the 4-to-12 density rules, not to divide the land into new parcels.

Washington passed HB 1110 in 2023, a statewide middle-housing law that requires larger cities to allow more homes on residential lots. Seattle carried out that requirement through the One Seattle Plan. The interim ordinance in mid-2025 met the state deadline, and the permanent One Seattle Plan zoning in early 2026 replaced it. So Seattle's rules are the local version of a state-wide policy, which is why other Washington cities are making similar changes.

Start with two things: whether your lot is within a quarter-mile of a major transit stop, and your lot size. Those two facts decide whether you are limited to the 4-home base or can reach 6, 9, or 12. Then look at the envelope rules, the 32-foot height, 50% lot coverage, and the floor-area ratio for your density, because those usually decide what physically fits. If you are near transit or building smaller units, you likely owe no parking, which frees up the lot and lowers the build cost.