How big can an Issaquah ADU be?
✓ Verified against code · August 19, 2026
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.
Citation: LUC 18.500.090(F)(2)
How current is this?
Issaquah’s ADU rules run under LUC 18.500.090 (Issaquah Land Use Code) (Ordinances 3092 / 3093). 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. We verified this answer against primary sources on August 19, 2026, and every change we catch is logged in the changelog.
More Issaquah ADU questions
- How long does an Issaquah ADU permit take?
- Do I need parking for an Issaquah ADU?
- Can I sell an Issaquah ADU separately?
- Can my ADU share the house's water meter?
- Does Issaquah offer pre-approved ADU plans?
All Issaquah ADU rules → · Compare Washington cities →
Not legal advice — lot-specific overlays can change the answer for your parcel. The citation above points at the governing code section; check it, or ask the city to confirm.