Seattle Middle Housing Under HB 1110: What Changed for Lot Owners

What state law requires

HB 1110 is codified at RCW 36.70A.635. Cities of 75,000 people or more must allow at least four units per lot on lots zoned mainly residential, and six within a quarter-mile walk of a major transit stop or when at least two units are affordable for at least 50 years. No parking can be required within a half mile of a major transit stop. Other cities are covered in the Washington HB 1110 guide.

How many units a Seattle lot allows

Seattle went past the state floor. An NR lot allows the greatest of:

• One unit per 1,250 sq ft of lot area for attached or detached homes

• One unit per 600 sq ft for stacked flats, with more possible when added requirements are met

• Four units

• Six units within a quarter mile of a major transit stop, or when at least two units are affordable

A 5,000 sq ft lot gets four units either way. A 7,500 sq ft lot gets six on lot area alone. ADUs count toward the total, and environmentally critical areas reduce density in proportion to the share of the lot they cover.

Floor area now follows the unit count

This is the change most owners miss. The floor area ratio (FAR) rises as density rises:

• 0.6 below one unit per 4,000 sq ft of lot area

• 0.8 from one unit per 4,000 sq ft to one unit per 2,201 sq ft

• 1.0 from one unit per 2,200 sq ft to one unit per 1,601 sq ft

• 1.6 at one unit per 1,600 sq ft or more

On a 5,000 sq ft lot, a single house is capped at 3,000 sq ft of floor area, while four units can share 8,000 sq ft. Stacked flats can reach 1.8 FAR, or 2.0 with a retained Tier 1 tree, two retained Tier 2 trees or a 0.6 Green Factor score. Lots under 5,000 sq ft get up to 2,500 sq ft regardless of FAR.

Height, setbacks and lot coverage

Base height is 32 feet plus pitched roof allowances, or 42 feet when the project keeps a Tier 2 tree, reaches 10 percent tree canopy at maturity, has three or more principal units behind a front setback of at least 20 feet, or pairs stacked units with a 0.6 Green Factor score. Front and rear setbacks drop from 15 feet to 10 feet at three or more units, and the rear setback is zero on an alley. Side setbacks average 5 feet with a 3 foot minimum, buildings sit at least 5 feet apart, and lot coverage tops out at 50 percent.

Parking, trees and design

Parking is one space per two units, and none within a half-mile walk of a major transit stop, for units of 1,200 sq ft or less, or for ADUs. New units also bring amenity area, tree planting and Tree Protection Code requirements, and design standards for pathways, entries, windows and doors. Unit lots have no minimum size, but a new parent lot under 5,000 sq ft cannot be created.

What is still moving

Draft Neighborhood Residential clean up legislation came out on 10-26-2026, with comments closed on 11-09-2026, and is headed to Council in late 2026. The Centers and Corridors rezone, sent to Council on 01-29-2026, is on hold while appeals of the city’s environmental impact statement proceed. A complete building permit application vests to the codes in effect on the day it is filed (RCW 19.27.095), so submittal timing can decide which version of the rules applies.

What to check before you design

Start with the lot, not the floor plan: measured lot area, walking distance to a major transit stop, critical areas, regulated trees and alley access. Each one moves the unit count, the floor area or the height. Backyard cottages have their own size limits, covered in the Seattle DADU and ADU guide.

How SASHKOV handles it

SASHKOV reads the lot against Ordinance 127376 before anyone draws, including the trees and critical areas that change the numbers. That work sits under Feasibility and Regulatory Strategy, and the wider picture is on the Middle Housing page. Where a building needs a licensed architect or engineer, SASHKOV brings them into the contract and carries the permit through SDCI review.

Own an NR lot in Seattle, or about to buy one? Send the address and what you want to build, and SASHKOV will confirm what the lot allows and map the permit path.