For years, off-street parking requirements were the single biggest barrier to ADU construction in Washington State. Many properties simply didn't have room for both an ADU and additional parking. That changed dramatically with House Bill 1337, which eliminated parking requirements for ADUs near transit — and in Seattle, that covers the vast majority of residential neighborhoods.
This guide explains the current parking rules, who qualifies for the transit exemption, and what this means for popular ADU types including garage conversions.
Not sure if your property qualifies? Our free feasibility study checks transit proximity as part of the analysis.
Seattle: No Off-Street Parking Required (Most Areas)
Under HB 1337, no off-street parking is required for ADUs located within half a mile of a major transit stop. Seattle is served by King County Metro bus routes throughout the city, and the Link Light Rail system (1 Line) and RapidRide corridors cover the most densely populated residential neighborhoods — meaning the vast majority of Seattle properties fall within this exemption radius.
In practical terms: if you live in most Seattle neighborhoods, you do not need to add any parking for your ADU. Your existing driveway and on-street parking are sufficient. This is a massive change from the pre-HB 1337 rules, which often required one or two dedicated off-street spaces per ADU.
King County Rules
For properties in unincorporated King County (outside Seattle city limits), parking rules are different. The county has been updating its ADU regulations to comply with state mandates, but rural properties typically have more lenient parking requirements anyway — because lots are larger and most properties already have ample driveway and on-site parking.
Smaller incorporated cities within King County — such as Enumclaw, Carnation, Snoqualmie, and North Bend — follow their own municipal codes, which are also being updated to comply with HB 1337. In areas served by King County Metro routes, the transit exemption applies wherever a fixed-route bus stop falls within half a mile.
For the specific rules affecting your property, see our comparison of Seattle vs King County ADU regulations.
Transit Proximity Exemptions
The key question is whether your property is within half a mile of a major transit stop. Here's how most Seattle neighborhoods stack up:
| Neighborhood | Parking Status | Transit Details |
|---|---|---|
| Capitol Hill | Exempt | Capitol Hill Link Light Rail station; dense RapidRide + Metro network |
| Beacon Hill | Exempt | Beacon Hill Link Light Rail station; multiple Metro routes |
| Columbia City | Exempt | Columbia City Link Light Rail station (1 Line) |
| Rainier Valley | Exempt | Multiple Link stations (Columbia City, Othello, Rainier Beach) |
| Fremont / Wallingford | Exempt | RapidRide D + multiple Metro routes; within ½ mi of Link connections |
| Greenwood / Phinney Ridge | Exempt | King County Metro routes along Greenwood/Phinney Ave N |
| Ballard | Exempt | RapidRide D Line; multiple Metro routes |
| West Seattle | Mostly Exempt | RapidRide C Line covers most of West Seattle; outlying streets: verify |
| Shoreline (unincorporated edge) | Check | Shoreline Link stations open 2024; confirm ½-mi radius for your parcel |
*Transit exemption based on half-mile radius from any fixed-route transit stop (Link Light Rail, RapidRide, King County Metro buses). Verify your specific property with our feasibility study.
What Counts as “Parking”?
Even for properties outside the transit exemption zone, the parking requirements are less onerous than you might think. Here's what typically satisfies the requirement:
Typically Counts
- Existing driveway space (even gravel or compacted surfaces)
- Tandem parking (cars parked one behind another)
- Carport or covered area (doesn't need to be an enclosed garage)
- Pervious paving or permeable surfaces
Good to Know
- On-street parking is NOT counted toward off-street requirements
- Standard stall size: 8.5' x 18' minimum
- ADA accessible spaces only required for commercial, not residential ADUs
Garage Conversion Parking Implications
One of the most common concerns we hear: “If I convert my garage to an ADU, do I need to replace the parking I'm losing?” Under the old rules, the answer was usually yes — which made many garage conversions impractical because there was nowhere to put the replacement parking.
Under HB 1337, the answer for most Seattle properties is no. The transit proximity exemption means you don't need to replace the garage parking. Your existing driveway (in front of where the garage was) and on-street parking are sufficient.
This change alone has made garage conversions one of the most cost-effective ADU options in Seattle. You're working with an existing structure, reducing construction costs, and you don't need to budget for building a replacement parking area.
Important note: Even though you don't legally need parking, consider your household's actual parking needs. If you have three cars and a single-car driveway, losing the garage means two cars on the street. Practically, most homeowners find that driveway parking plus on-street works fine.
Frequently Asked Questions
Do I need to add parking to build an ADU in Seattle?
In most cases, no. Under HB 1337, cities cannot require off-street parking for ADUs within half a mile of a major transit stop. Since most Seattle neighborhoods are within this distance of a King County Metro bus route, the vast majority of properties are exempt from any ADU parking requirement.
If I convert my garage to an ADU, do I need to replace the parking?
Under HB 1337, the loss of parking from a garage conversion does not need to be replaced if your property qualifies for the transit proximity exemption. Since most Seattle properties do qualify, you can convert your garage without adding new parking spaces. Check our feasibility study to confirm your specific property.
What counts as a "major transit stop" for the parking exemption?
Washington State defines this broadly. It includes stops served by fixed-route transit (bus routes with regular schedules). In Seattle, this means Link Light Rail stations, RapidRide corridors (A through H lines), and King County Metro fixed-route buses all count. The half-mile radius from any of these stops covers the vast majority of Seattle residential neighborhoods. The exemption does not require high-frequency service — just a fixed route.
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