168,655
98%
clear the legal screen
under the reviewed NR, lowrise, midrise, and highrise rule sets
Backyard Cottage Atlas
Where a cottage looks possible — and where our data stops
This is a citywide screening view, not a verdict on any lot. It shows how many Seattle residential parcels clear a rule and footprint check, separates measured constraints from missing evidence, and names the data work still left to do.
What the current screen says
Denominator: 171,938 non-civic parcels in Seattle residential zone families. Each check is independent; these are not steps in a single conversion funnel.
130,267
76%
have a measurable footprint fit
for the 16 × 30 ft reference cottage footprint
37,633
22%
hit a measured geometry limit
including setbacks, standing footprints, small fragments, and narrow slivers
4,038
2%
still need a physical answer
because a required screen input is still unavailable
Drainage review is not sewer failure
41,070 parcels are in mapped CSO basins and need drainage-control review. Only 13,352 intersect the separately mapped capacity-constrained system layer.
The economics are not ready for a citywide verdict
Every included parcel still carries the same uncalibrated cost caution. The ZIP-level rent sensitivity belongs in methodology, not in a ranking of neighborhoods.
Data cleanup queue
What this audit says we should fix next
These are gaps in our evidence or processing—not reasons for a homeowner to abandon a project.
The current artifact has no unresolved items in this priority cleanup queue. Measured site constraints remain findings, not data defects.
Open evidence work
Each brief states the size of a remaining evidence problem, what already exists, and the artifact needed to close it. They are research briefs, not project recommendations.
Financial plausibilityNeeds evidence
Calibrate the DADU construction-cost screen
All 171,938 included parcels carry the published uncalibrated-cost caution, so the financial result remains a planning sensitivity rather than an empirical Seattle cost finding.
171,938 parcels · 100% of 171,938 · Seattle
Read the full brief →Verification readinessNeeds infrastructure
Define a parcel-level sewer-capacity verification path
The corrected artifact identifies 13,352 included parcels that intersect a mapped capacity-constrained sewer-system area and need review against actual available capacity.
13,352 parcels · 8% of 171,938 · Seattle
Read the full brief →Open the technical evidence passport
Full stage counts, constraint distribution, universe filters, version identifiers, and methodological limitations.
Versioned housing-screen evidence passport
Backyard cottage / DADU screen
Where screened capacity remains, where it is lost, and which evidence is still missing under evaluation gap-dadu-v1.7.
Declared universe
226,166
Included parcels
171,938
76% of universe
Explicit exclusions
54,228
Independent screening checks
These checks are not a sequential funnel. A parcel can pass a later check while an earlier one is blocked or unknown.
| Stage | Pass | Blocked | Unknown | Not evaluated |
|---|---|---|---|---|
| Legal capacity98% of included | 168,655 | 0 | 3,283 | 0 |
| Physical fit76% of included | 130,267 | 37,633 | 4,038 | 0 |
| Financial plausibility72% of included | 124,307 | 47,631 | 0 | 0 |
| Affordable scenario and program applicability76% of included | 130,267 | 0 | 0 | 41,671 |
| Verification readiness46% of included | 79,138 | 0 | 92,800 | 0 |
Most common constraints and gaps
Income after capacity billing does not cover debt service
blocking · needs affordability
47,631
28%
Rear-yard clear span is too narrow
blocking · needs plan
21,167
12%
Remaining fragment is below 150 square feet
blocking · needs plan
12,666
7%
Only a sub-7-foot sliver remains
blocking · needs plan
1,726
1%
Rear-yard buildable area is too small
blocking · needs plan
1,059
1%
Standing building consumes the envelope
blocking · needs plan
1,003
1%
Setbacks consume the buildable envelope
blocking · needs plan
12
0%
Critical-area severity unreviewed
evidence gap · needs evidence
54,447
32%
Drainage-control requirements unreviewed
evidence gap · needs infrastructure
41,070
24%
Sewer capacity unreviewed
evidence gap · needs infrastructure
13,352
8%
Buildable envelope missing
evidence gap · needs evidence
4,583
3%
Building footprint not linked to this lot
evidence gap · needs evidence
4,038
2%
Universe: Parcels with a current enriched warehouse row, a resolved zoning category in a residential zone family, a non-excluded jurisdiction, and a non-civic present use.
Filters: outside_seattle_city_limits: Parcel resolves outside Seattle city limits, which is outside this artifact's jurisdiction.; zoning_unresolved: No zoning category resolved for the parcel, so no rule set applies.; civic_or_institutional_present_use: Parcel carries a civic, institutional, or park present use, so a household backyard cottage is out of scope.; non_residential_zone_family: Parcel sits in a commercial, mixed-use, downtown, or industrial zone family, where a household backyard cottage is not the applicable housing instrument.
Evidence manifest: gap-atlas-manifest:backyard-cottage:v1:4fbf6f1e
Public-data screen only. It includes no site visit, survey, title review, or permit determination. Legal capacity comes from joined zone rules; physical fit comes from the citywide parcel screen. A parcel can pass one and not the other. The citywide physical screen covers the NR, RSL, LR, MR, HR, and legacy SF residential zone families. Outside them physical fit is reported as unknown, never as a physical failure. Current SMC 23.42.022 (Ord. 127375/127376, 2025) allows accessory dwelling units as a housing use in every zone where housing uses are allowed. The former 2023 lowrise principal-unit-type gate and 650-square-foot cap no longer apply; the current cap is 1,000 square feet. A parcel that intersects the official Seattle Shoreline Environments overlay is reported as legally unknown, not blocked. Current SMC 23.42.022.A requires Shoreline District ADUs to comply with Chapter 23.60A, which this screen has not read per environment; earlier evaluations (through gap-dadu-v1.6) reported the overlay as a prohibition. Standing structures are measured spatially against the lot (dadu-footprint-evidence-v1), not by the footprint layer's parcel identifier. A lot with a King County building record but no measured footprint is reported as physically unknown; a lot with neither is reported with a no-principal-dwelling caution. The physical screen treats every standing structure as immovable. Where a lot fails only because of its own garage or outbuilding, the screen also reports whether the reference cottage would fit with the house alone retained; that is a caution on a blocked result, not a pass. Financial plausibility applies a published screening rule to explicit planning assumptions and a HUD SAFMR rent basis. It is not a bid, quote, appraisal, or forecast, and no Seattle cost calibration supports it. The financial stage varies only by ZIP-level one-bedroom HUD SAFMR. All parcels in the same SAFMR geography receive the same result under the citywide cost assumptions; this is not parcel-specific financial evidence. Financial geography patterns are rent-basis patterns, not observed construction-cost or project-outcome patterns. They must not be used to deprioritize investment in the neighborhoods they name. Public program applicability describes whether a listed program reaches this site. Household eligibility — income, ownership, occupancy, disability, financing — is never collected or inferred. The first detected blocker is the first blocking condition under the published stage and within-stage detection order, and attribution is withheld when an earlier stage is unknown. It is not a claim that other constraints matter less. Stages are evaluated independently wherever their inputs allow, so a later-stage blocker does not imply that earlier stages passed. Every share in this artifact is reported against its denominator: included parcels in the declared evaluation universe. Excluded parcels are counted by reason and are never redistributed into stage results.