How big can a Renton ADU be?
✓ Verified against code · August 19, 2026
1,000 sq ft of gross floor area (and building area). Converting one full floor of your existing house can reach 1,250 sq ft, and PRADU pre-approved plans are exempt from the cap entirely.
Citation: RMC 4-2-110C; fns 40–41, 26
How current is this?
Renton’s ADU rules run under RMC 4-2-110C (Renton Municipal Code) (Ordinance 6160 (amended by Ord 6173)). Renton adopted its HB 1337 compliance package in June 2025 (Ord 6160) and amended it again five months later (Ord 6173, November 2025) — two rule changes in one year. Its PRADU pre-approved plan program is among the most generous in the state. We verified this answer against primary sources on August 19, 2026, and every change we catch is logged in the changelog.
More Renton ADU questions
- How many ADUs can I build on a Renton lot, and do I have to live there?
- What is Renton's PRADU program actually worth?
- Do I need parking for a Renton ADU?
- Can I convert an existing garage or shed?
- Are Renton's PRADU plans exempt from height limits?
All Renton 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.