Issaquah ADU rules
✓ Verified against code · August 19, 2026
Current rules under LUC 18.500.090 (Issaquah Land Use Code), adopted by Ordinances 3092 / 3093, in effect since May 27, 2025. Issaquah adopted its ADU package (Ord 3092) and parking overhaul (Ord 3093) together in May 2025, alongside its middle-housing ordinance. Unusually for the region, Issaquah publishes actual permit review-time targets.
Common questions, answered from the code
How big can an Issaquah ADU be?
1,000 sq ft each, not counting garages, sheds, or decks — but check the other direction too: your main house must be at least 25% larger than your biggest ADU, which on a modest home can be the binding limit.
LUC 18.500.090(F)(2) · Permalink
How long does an Issaquah ADU permit take?
Issaquah is one of the few cities that publishes targets: four weeks for first review, three for the second round, one week for third and later — measured from fee payment. Budget for two rounds on a custom design.
City Target Review Times handout (April 2026) · Permalink
Do I need parking for an Issaquah ADU?
No — the minimum is zero. Unusually, there's also a maximum: one space per ADU, and tandem parking counts.
Table 18.604.080(A); LUC 18.500.090(F)(5) · Permalink
Can I sell an Issaquah ADU separately?
Yes — the 2025 ordinance struck owner-occupancy entirely, and the code expressly protects condominium conveyance of ADUs.
LUC 18.500.090(F)(8) · Permalink
Can my ADU share the house's water meter?
Possibly — sharing the principal dwelling's connection and meter is allowed if fixture count and fire-flow demands are met; the city reviews capacity with your water/sewer availability forms at submittal.
LUC 18.500.090(F)(7); ADU submittal requirements · Permalink
The rules at a glance
| ADUs allowed per lot | Two ADUs in any combination of attached or detached, with a single-family residence or with middle housing (the lot must meet density and minimum lot size for the principal unit; nonconforming lots also qualify for up to two).LUC 18.500.090(F)(1), (C) |
| Maximum size | 1,000 sq ft each, excluding nonliving areas like garages, storage sheds, and decks (unless the ADU is located in them). Internal conversions and existing-structure conversions may exceed 1,000 sq ft if no exterior expansion is needed. One catch: the principal home must have gross floor area at least 25% larger than the largest ADU.LUC 18.500.090(F)(2)(a)–(c) |
| Detached ADU height | No separate DADU cap — ADUs comply with the principal unit's height per Ch. 18.404 (roughly 30 ft in most single-family zones).LUC 18.500.090(F)(3) |
| Detached ADU setbacks | Standard zone setbacks — with one exception: new ADUs face no rear-yard setback where the rear yard abuts an alley (unless the city routinely plows snow on it).LUC 18.500.090(F)(4)(a)(1) |
| Off-street parking | Zero minimum — and a maximum of one space per ADU. Tandem parking satisfies any space you choose to provide.Table 18.604.080(A) (Ord 3093); LUC 18.500.090(F)(5) |
| Owner-occupancy | None — Ordinance 3092 struck the owner-occupancy criterion and covenant. ADUs can be sold and owned separately, and the code bars prohibiting condominium conveyance.Ord 3092 Exh. C; LUC 18.500.090(F)(8) |
| Lot coverage / floor area | ADUs don't count toward lot density when associated with a detached single-family home (they do count with middle housing). Standard zone impervious-surface and coverage limits apply.LUC 18.500.090(D)(2) |
| Permit path & timeline | Level 1 (administrative) review plus a building permit, e-submittal only via MyBuildingPermit.com. Published target review times: four weeks for first review, three for second, one for third and later — targets start when fees are paid.LUC 18.500.090(B)–(C); city Target Review Times handout (April 2026) |
Worth knowing
- The 25%-larger principal-unit rule is unique in the region — on a small house, it can bind before the 1,000 sq ft cap does.
- Issaquah sets a parking MAXIMUM for ADUs (one space) — most cities only set minimums.
- A 4-ft-wide walkway to the ADU entrance is required, and a street-facing ADU door must be screened or mitigated.
- ADUs may share the principal dwelling's utility connection and meter if fixture counts and fire-flow demands pencil out — the city reviews capacity at submittal.
- An explicit legalization path exists for unpermitted pre-existing ADUs via inspection.
- No pre-approved ADU plan program — the city's FAQ says so explicitly.
On our watchlist
Ordinance 3114 (October 2025) — subject matter unverified; we confirm it didn't amend the ADU or parking chapters on the next pass.
The 'Lot Density Covenant' section (retitled from the old owner-occupancy covenant) is ambiguous about whether any recorded covenant is still required for new ADUs — worth a one-line confirmation with Issaquah CPD.
Check your parcel
The rules above are citywide — what you can build depends on your lot’s zone, size, and setbacks. Look yours up on the official viewers:
- King County Parcel Viewer
- King County Assessor Property Search (eRealProperty)
- Issaquah GIS map (General Viewer)
Primary sources
- Ordinance 3092 (ADU standards, signed)
- Ordinance 3093 (parking, signed)
- City ADU page + FAQ
- Target review times
Other Washington cities
Bellevue · Bothell · Burien · Edmonds · Everett · Kent · Kirkland · Lynnwood · Olympia · Redmond · Renton · Sammamish · Seattle · Shoreline · Tacoma
Not legal advice. Every fact above cites the code section it comes from — check the cite, or ask your city’s planning department to confirm your specific lot. Spotted an error or a new ordinance? See about to reach us; corrections are logged in the changelog.