DADU feasibility · Beacon Hill
Building a DADU in Beacon Hill
Beacon Hill has the highest detached-house share of any area in this set and the lightest tree canopy — an unusually clean combination for a cottage.
This profile is measured from City of Seattle open data across 3,449 parcels in Beacon Hill — not estimated, and not the same numbers as any other neighborhood on this site.
Lot sizes in Beacon Hill
Lots are solidly mid-size, with most above 5,000 sq ft. Combined with a housing stock that is nearly nine-tenths detached single houses, the typical Beacon Hill parcel is a straightforward DADU candidate on geometry alone.
Parcel counts by lot size, Beacon Hill. Source: King County parcels via Seattle's ADUniverse dataset.
32% of parcels here are under 5,000 sq ft and 68% are 5,000 sq ft or larger — a high share among the 18 areas profiled here. Seattle repealed the old 3,200 sq ft minimum lot area for a DADU, so small lots are no longer excluded; they are simply governed by the floor-area budget instead.
What the ground looks like
The ridge line carries steep slope along its edges, but the plateau is stable and there is essentially no mapped landslide-prone ground. Canopy is the lowest in this set, which means fewer Tier 2 and Tier 3 tree conflicts than almost anywhere else in Seattle.
Beacon Hill against the median of the 18 Seattle areas profiled here. Hazard layers clipped to the neighborhood boundary; canopy is area-weighted by census block group.
What decides feasibility here, in order
Ranked by what this neighborhood's own measurements say — not a generic checklist.
-
01
Side sewer, water and electrical capacity
19% of buildings here predate 1940 and 43% were built between 1940 and 1975. Older stock means older side sewers and smaller electrical services — the two utility findings that most often reset a DADU budget.
-
02
Slope and landslide-prone ground
8% of Beacon Hill is mapped as steep slope (40% or greater) and 0% as potential landslide area, against Seattle medians of 7.7% and 4.4% across the areas profiled here. Land inside an Environmentally Critical Area under SMC 25.09 triggers additional review and, in practice, a geotechnical report before design.
-
03
Liquefaction and soil conditions
7.8% of Beacon Hill sits on mapped liquefaction-prone soils (Seattle median here: 8.7%). This rarely stops a project, but it changes foundation design and belongs in the budget before you price a build.
-
04
Physical fit on a small lot
32% of parcels here are under 5,000 sq ft. Lot size no longer disqualifies a DADU, but on a tight lot the lot-wide FAR and lot-coverage budget — which ADU floor area now counts toward — usually binds before setbacks do.
-
05
Protected trees
Tree canopy covers 16.4% of Beacon Hill (Seattle median here: 26.9%). Seattle's tree code (SMC 25.11) protects trees by tier, and a Tier 2 tree with its root protection area falling across your rear yard can move or shrink a cottage even on a large lot.
Zoning and utilities
Zoning mix
- SF 50002,727 parcels
- SF 7200260 parcels
- LR2120 parcels
- LR389 parcels
- MR71 parcels
88.2% of parcels are Neighborhood Residential or Residential Small Lot; 7.4% are Lowrise. Zone labels reflect the parcel dataset's legacy single-family categories, which map into today's Neighborhood Residential zone under Ordinance 127376.
Housing age
- Before 194019%
- 1940 – 197543%
- After 197528%
Mid-century stock on a ridge. Confirm panel capacity; the sewer runs are generally shorter and simpler than the north end's deep lots.
Beacon Hill DADU questions
Can I build a DADU in Beacon Hill?
In almost all cases the zoning allows it. 88.2% of parcels in Beacon Hill sit in Neighborhood Residential or Residential Small Lot zoning, where detached accessory dwelling units are permitted, and Seattle removed both the old minimum-lot-size test and the owner-occupancy requirement. The real question is whether a compliant cottage physically fits your lot and whether utilities can serve it.
How big can a DADU be in Beacon Hill?
The citywide caps apply: 1,000 sq ft of gross floor area for an ADU with up to two bedrooms, or 1,200 sq ft with three or more. On top of that, your lot has a single FAR and lot-coverage budget shared with the existing house — which is what actually limits most projects. 68% of Beacon Hill parcels are 5,000 sq ft or larger, so whether you reach the cap depends heavily on which block you are on.
What is most likely to block a DADU in Beacon Hill?
Side sewer, water and electrical capacity — 19% of buildings here predate 1940 and 43% were built between 1940 and 1975. Older stock means older side sewers and smaller electrical services — the two utility findings that most often reset a DADU budget.
Do I need a feasibility study before designing a DADU in Beacon Hill?
You are not required to have one. But the checks that decide feasibility — setbacks against the existing house, FAR headroom, tree tiers, mapped critical areas, side sewer condition, and construction access — are all cheaper to answer before you commit to an architect or a plan set than after. In Beacon Hill specifically, start with the side sewer and the panel — on flat, stable ground like this, utilities are what most often reset the budget.
Next step
Run these checks on your own Beacon Hill lot.
This page tells you what Beacon Hill looks like as a whole. The Seattle DADU Pro Guide walks your specific address through the same review — setbacks and FAR headroom, tree tiers, mapped critical areas, side sewer and panel capacity, the permit roadmap, and a scoring template you fill in yourself.