The 600 SF ADU: The Efficiency Sweet Spot

If ADU sizes had a "most valuable player," 600 SF would win most years. It's the smallest size that delivers a real one-bedroom home — and that unlocks everything.

What 600 SF holds: a genuine separated bedroom (11'×11' or so, with closet and egress window), a full bathroom, a real kitchen with counter space on both sides of the sink, and a living area big enough for a sofa, TV, and small dining table. Nobody has to eat on the couch. This is the difference between "a unit" and "a home."

Why the economics sing. Compared to 400 SF, you've added roughly $70K of construction (at planning-level rates) but jumped rental categories — from studio pricing to one-bedroom pricing, and from solo tenants to couples. Compared to 800 SF, you've saved roughly $70K while keeping most of the rent. In many California markets, 600 SF one-bedrooms sit at the top of the rent-per-dollar curve.

Design notes at this size:

• An open kitchen-living combo keeps the shared space feeling large; spend the walls on the bedroom
• In-unit laundry (stacked washer/dryer in a closet) fits at this size and tenants pay for it
• A small covered porch or patio effectively extends the living room outdoors

Who it serves: long-term tenants (solo or couples), a parent with independent habits, an adult child, or you — several of our clients build a 600 SF unit intending to downsize into it eventually.