A Seattle lot can look like four townhomes on a listing and turn out to be one house and a tree. Most of the difference comes from five checks: the unit count the lot actually allows, critical areas, large trees, utilities, and how long each agency takes to answer. Each one has an official answer, and each is easier to get before closing than after.
Count the units the lot actually allows
Since 01-21-2026, Seattle Neighborhood Residential lots allow the greatest of four units, one unit per 1,250 sq ft of lot area, or six units within a quarter mile of a major transit stop or with at least two affordable units. Stacked flats allow one unit per 600 sq ft. Floor area grows with the unit count: 0.6 FAR for a single house, up to 1.6 at one unit per 1,600 sq ft of lot area or more. Two lots that look alike on a listing can hold very different projects, so start from measured lot area and the walking distance to transit, not the asking price.
Check for environmentally critical areas first
Seattle regulates landslide-prone areas (including steep slopes), peat settlement, liquefaction, abandoned landfills, flood-prone areas, wetlands, riparian corridors within 100 feet of a water body, and fish and wildlife habitat. Critical areas also reduce middle housing density in proportion to the share of the lot they cover.
Exemption before the permit. If the work qualifies, SDCI can exempt it from the ECA rules. The exemption decision must be in hand before you apply for the building permit.
Site visit. Most requests need a pre-application site visit, and the application usually carries a site plan plus a geotechnical report or topographic survey.
Timing. SDCI aims to finish exemption review within 2 weeks. Build that into the feasibility period.
Find the large trees
Under Seattle's tree protection code, a Tier 2 tree is 24 inches in diameter at standard height or larger, and a Tier 3 tree is 12 to 24 inches. In Neighborhood Residential and the other residential and commercial zones, a Tier 2 tree can come out only if it is hazardous, an emergency, or must be removed to reach the development capacity the code allows. Tier 3 trees can be removed with a development permit. Removed trees require replacement or a payment in lieu, paid before SDCI approves the removal. One large tree in the wrong spot can move the building footprint.
Confirm utilities and access
Seattle Public Utilities confirms water, drainage and wastewater service through an availability certificate. Ask early whether the lot is served by the main in front of it, how stormwater will be handled and whether a side sewer has to be extended. Alley access changes rear setbacks and parking options.
Line the deadline up with the agencies
Zoning can be read in an afternoon. A critical area exemption, a utility answer or a tree evaluation can take weeks. If an answer will come back after the inspection period ends, flag it before you waive contingencies. An unanswered question is not a green light.
Know which rules will apply
A complete building permit application vests to the zoning and building codes in effect on the day it is filed (RCW 19.27.095). Seattle's Neighborhood Residential clean up legislation is headed to Council in late 2026, so the filing date can decide which version of the rules governs the project.
Frequently Asked Questions
How many units can a Seattle Neighborhood Residential lot hold?
The greatest of four units, one unit per 1,250 sq ft of lot area, or six units within a quarter mile of a major transit stop or with at least two affordable units. Stacked flats allow one unit per 600 sq ft.
Do I need an ECA exemption before applying for a Seattle permit?
If the project qualifies for an exemption, the decision must be received before you apply for the building or master use permit. SDCI aims to finish review within 2 weeks, and most requests need a site visit.
Can I remove a large tree on a Seattle lot I am developing?
A Tier 2 tree, 24 inches in diameter or larger, can be removed only if it is hazardous, an emergency, or must come out to reach the development capacity the code allows. Tier 3 trees, 12 to 24 inches, can be removed with a development permit. Replacement or a payment in lieu is required.
Sources
Insights are general information researched from published sources on the date shown. Rules change, so confirm with the permitting authority before you act.
