ADU builders
Backyard cottage builders: what to check
By the HyreADU research desk. Last checked .
The short answer
A backyard cottage is a detached ADU by another name. Seattle uses the term for a detached accessory dwelling unit (DADU). In California the same unit is a detached ADU under Gov. Code § 66323. The rules and the builder license follow the legal category, not the name on the brochure.
What the term means where
Seattle’s building department calls a backyard cottage a detached accessory dwelling unit, permitted as a separate dwelling, and offers pre-approved designs. California law says detached ADU. Some builders also say casita or granny flat. Ask which legal category the unit will be permitted as.
Rules follow the category
In California a detached unit with four-foot side and rear setbacks must be approved if it meets the code (Gov. Code § 66323). In Seattle, the city’s own ADU rules apply, and they have changed recently, so check the city’s current page.
For how many ADU permits Seattle has issued each year, see our Seattle ADU permit data. A tiny house on wheels is not a backyard cottage in Seattle and cannot be lived in within city limits.
Checking a cottage builder
In California, a B General Building license. In Washington, a registered contractor with the state Department of Labor and Industries. Ask for finished units in your city and an itemized bid. See how to find a good ADU contractor.
What to do next: read the questions to ask an ADU builder, check what decides ADU cost, then tell us about your project. Matching is not live yet, so we reply with information, not a quote.
Get ADU optionsQuestions
Is a backyard cottage the same as a tiny house?
A tiny house on a foundation can be an ADU. One on wheels is usually a vehicle, not a dwelling.
Do backyard cottages need parking?
Seattle’s 2023 guidance said no parking is required for an ADU; check the city’s current rules. California caps ADU parking and waives it in many cases.
Can I rent a backyard cottage?
Usually, subject to local rules. California lets cities require rentals of 30 days or more (Gov. Code § 66315).
Does HyreADU list cottage builders?
No. We publish no ranked list and have no partner builders.
Sources
- Seattle SDCI, Accessory Dwelling Unit (backyard cottage). Checked October 27, 2026.
- Gov. Code § 66323 (by-right ADUs, utility connections). Checked September 5, 2026.
- Gov. Code § 66315 (no extra standards, 30-day rentals). Checked September 5, 2026.
- CSLB Fast Facts: Accessory Dwelling Units (2025). Checked October 27, 2026.
HyreADU is a publisher. It does not design, permit or build ADUs, has no partner builders, and gives no legal, tax or engineering advice. Rules vary by state and city; California rules are labeled as such.