How Many Homes Can You Build on a Seattle Lot?
If you own a detached house on a Seattle lot, your zoning answer used to be one home, plus up to two accessory units. That's changed. Under Seattle's middle housing rules, most lots in Neighborhood Residential (NR) zones now allow four homes, and some allow six.
The count is the easy part. Whether those homes will actually fit on your lot takes a few more checks. We'll walk through them in order.
The short answer
Seattle's permanent middle housing legislation took effect on January 21, 2026, replacing interim rules adopted in mid-2025 to comply with Washington's HB 1110, the state middle housing law.
In NR zones, you're now allowed at least four homes on every lot, regardless of size. You can have six when one of two conditions holds: the lot is within a quarter-mile walk of a major transit stop, or two of the homes are affordable housing.
A major transit stop is a light rail station or a bus rapid transit stop, such as a RapidRide line, and it's a walking distance, not a straight line.
What sets the number
Start with the zone. NR covers most of Seattle's detached-house neighborhoods, and every count in this guide applies there. Lowrise, commercial, and other zones use different limits, so confirm your zone before you use any number here.
Next comes lot area. Base density is one home per 1,250 square feet of lot area, and the four-home floor sits underneath that formula, so a 3,750-square-foot lot still gets four. If your lot is bigger, the formula can allow more than four, and sometimes more than six, with no transit or affordability condition involved.
Finally, two conditions lift the floor to six: a quarter-mile walk to major transit, or two affordable homes in the project. Either one does it on its own.
Your lot | v Is the zone Neighborhood Residential (NR)? |-- No -> Different limits apply. Confirm the zone first. | Yes | v Base count: 1 home per 1,250 sq ft of lot area, and never fewer than 4 homes on any lot | v Within a 1/4-mile walk of a major transit stop, OR will 2 of the homes be affordable housing? |-- Yes -> The floor rises to 6 homes |-- No -> The count stays at 4, or the formula result if higher | v Then check the fit: coverage, floor area, height, setbacks, critical areas, trees, existing buildings
The other route: keep the house, add ADUs
Middle housing isn't the only way to add homes. If you're keeping the existing house, Seattle's ADU rules let you add two accessory dwelling units alongside the main home.
Your two ADUs can be attached, detached, or one of each. A detached ADU (a DADU, or backyard cottage) can stand in the rear yard. Each ADU can be up to 1,000 square feet, or 1,200 square feet with three or more bedrooms. There's no owner-occupancy requirement, so you don't have to live on the lot. The standards sit in SMC 23.42.022.
Add two ADUs to an existing house and you've got three homes, one fewer than the middle housing floor. The trade is that the house stays standing. One limit worth knowing: ADUs are part of the count, not a bonus on top of it. A project already at the four- or six-home count can't add two ADUs beyond it.
Allowed is not the same as fits
A unit count is a legal ceiling, not a site plan. Four checks decide whether you can actually draw the allowed homes on the lot:
- Lot coverage. Your buildings can cover up to 50 percent of the lot, or 60 percent for stacked flats.
- Height. The NR height limit is 32 feet, rising to 42 feet when certain standards are met.
- Setbacks. Yards were replaced with setbacks: 10 feet front, 5 feet sides, 10 feet rear, or zero at the rear with an alley.
- Open space and floor area. At least 20 percent of the lot stays open. Floor area is capped by a ratio that rises with unit count, up to 1.2.
For the arithmetic of how floor area, coverage, and placement interact on a single lot, see our guide to FAR, lot coverage, and the footprint that actually fits.
Worked example: a hypothetical 5,000-square-foot lot
Take a hypothetical lot: 5,000 square feet, NR zone, mid-block, no alley, a house of about 1,200 square feet, no mapped critical areas. Teaching assumptions, not a real parcel.
Count first: 5,000 รท 1,250 = 4 homes, matching the floor, so the count is four. The lot isn't within a quarter-mile walk of a major transit stop, and no affordable homes are proposed, so neither condition lifts it. Next to a RapidRide stop, the same lot's floor would be six.
You've got two ways to put homes on this lot: replace the house and build up to four new homes, or keep the house and take the ADU route, which gives three homes in total (the house plus two ADUs of up to 1,000 square feet each).
Here's the fit. Four new homes share a coverage cap of 2,500 square feet of footprint (50 percent of 5,000), under a 32-foot height limit. Setbacks take 10 feet off the front, 5 feet off each side, and 10 feet off the rear, and at least 1,000 square feet stays unbuilt as open space.
Fitting four homes inside that envelope takes design work: access paths, stairs, and separation between buildings all use room the raw areas don't show. The count says what's allowed. The envelope says what's possible.
What can still change the answer
A few site facts can narrow your project without changing the legal count. Environmentally critical areas don't count toward the lot area used in the calculations, so a mapped steep slope or wetland shrinks the area under your coverage and floor-area math. A large tree the code requires you to keep takes space out of the envelope. An unconfirmed sewer connection can hold up a layout that works on paper.
| Check | What it decides | Where the answer comes from |
|---|---|---|
| Zone | Which rulebook applies | The city zoning map |
| Lot area and density | The base count, with a floor of four | The parcel record and code density standards |
| Transit or affordable homes | Whether the floor rises to six | Walking distance to a major transit stop; the project proposal |
| Coverage, height, setbacks, floor area | Whether the allowed homes fit | The zone's development standards |
| Site conditions | Whether the fit survives the actual lot | Critical-area maps, tree records, utility records |
We've covered the record-keeping side in two other guides. The parcel evidence sheet is where you'd record each answer next to its source. How to read a blank constraint map explains what an empty map layer does and does not prove.
Getting a number for one specific lot
If you want a first-pass count for a real address, run it through LotFactor's analyzer. It brings the parcel record, zoning, mapped constraints, and transit context into one view and models the scenarios your lot supports. A free account includes 100 property searches a month, and you don't need a credit card.
Treat the result as a starting point for due diligence, not a permit decision. The count still needs confirmation against the current code, and for most projects you'll want a conversation with SDCI and a designer first.
Sources checked : SDCI, "ADUs and Middle Housing" and "New Middle Housing Codes to Boost Housing Supply"; Seattle OPCD, One Seattle Plan (CB 120993, effective Jan 21, 2026); Ordinances 127211, 127219, 127375, 127376; SMC 23.42.022.