Constraint and Gap Atlas
Seattle allows backyard cottages on most residential lots. This is an account of what happens between that permission and a cottage actually being buildable — measured across every parcel in the city, one stage at a time.
Most of what follows is a description of what we do not yet know. That is deliberate. A gap we can name and count is one somebody else can close, and the briefs below say exactly what evidence would close each one.
Evaluation gap-dadu-v1.2+assumptions-2026-Q2+financial-v1+programs-2026-06-23. These are automated screens over public data, not site investigations, permit decisions, or advice. Every count below is reported against the universe stated in the passport.
Versioned housing-screen evidence passport
Where screened capacity remains, where it is lost, and which evidence is still missing under evaluation gap-dadu-v1.2.
Declared universe
225,958
Included parcels
186,364
82% of universe
Explicit exclusions
39,594
| Stage | Pass | Blocked | Unknown | Not evaluated |
|---|---|---|---|---|
| Legal capacity66% | 123,890 | 0 | 62,474 | 0 |
| Physical fit69% | 128,438 | 40,737 | 17,189 | 0 |
| Financial plausibility90% | 167,817 | 18,377 | 170 | 0 |
| Affordable scenario and program applicability69% | 128,438 | 0 | 0 | 57,926 |
| Verification readiness30% | 56,393 | 0 | 129,971 | 0 |
financial cost basis uncalibrated
caution · needs evidence
186,364
100%
financial cost range straddles threshold
caution · needs affordability
131,590
71%
program household eligibility unknown
caution · needs affordability
128,438
69%
legal zone family unverified
evidence gap · needs policy
62,474
34%
verification zone rules unverified
evidence gap · needs policy
62,474
34%
physical tree canopy review
caution · needs stewardship
60,857
33%
physical eca overlap
caution · needs evidence
60,550
32%
verification eca severity unreviewed
evidence gap · needs evidence
60,550
32%
infrastructure sewer capacity review
caution · needs infrastructure
57,119
31%
verification sewer capacity unreviewed
evidence gap · needs infrastructure
57,119
31%
physical dadu screen failed
blocking · needs plan
40,737
22%
physical steep slope
caution · needs plan
39,915
21%
Universe: Parcels with a current enriched warehouse row, a resolved zoning category, 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.
Evidence manifest: gap-atlas-manifest:backyard-cottage:v1:b4ec2746
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 only covers the NR, RSL, LR, and SF zone families. Outside them physical fit is reported as unknown, never as a physical failure. 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.
Each brief takes one recurring constraint and states its scale, what currently exists to address it, the capability that is missing, and the next artifact somebody would have to produce. None of them is a request for a proposal or an offer of work.
The DADU artifact reports legal capacity as unknown for 62,474 included parcels because their zone-family rules have not completed the published verification path.
62,474 parcels · 34% of 186,364 · Seattle
Read the full brief →The general detached-cottage screen reports a physical-fit failure for 40,737 included parcels, but its current warehouse flag does not identify which dimension, shape, access, or envelope condition bound the result.
40,737 parcels · 22% of 186,364 · Seattle
Read the full brief →All 186,364 included parcels carry the published uncalibrated-cost caution, so the financial result remains a planning sensitivity rather than an empirical Seattle cost finding.
186,364 parcels · 100% of 186,364 · Seattle
Read the full brief →The artifact identifies 57,119 included parcels where mapped sewer risk or a drainage-control trigger requires review against actual capacity.
57,119 parcels · 31% of 186,364 · Seattle
Read the full brief →