Burien has its own ADU size, parking and permit rules. A useful city guide should make those local choices clear rather than reading like a builder’s sales page.
This independent guide is not the City of Burien or a contractor. Confirm the adopted code and property with Community Development.
What does Burien’s current code say?
Burien’s 2025 changes include BMC 19.17.070. The text allows up to two ADUs with a main home and generally limits them to 1,000 square feet. It also describes a possible exception for using current space in a building at least five years old.
Read the whole current section and confirm the lot. A summary of unit count and size does not answer placement, height, parking, utilities or building-code rules.
How should a Burien property be screened?
Collect the parcel, zoning, current dwelling and survey or site-plan details. Review:
- planned number and combination of ADUs.
- unit type and floor area.
- yards, coverage, height and building placement.
- trees, slope, drainage and retaining walls.
- driveway, alley and work access.
- sewer, water and electrical routes.
- existing garage or basement condition.
- easements or title restrictions.
Burien has varied slopes and neighborhoods. Tight access or drainage can control the project even when the unit type is allowed.
Use the early site-check guide to record site facts before plan selection.
Which ADU path should be compared?
A detached unit offers privacy but needs a full foundation, shell and utility route. An attached unit changes the main home. A garage or basement may reuse space, but its structure, moisture, height, fire safety and systems need review.
If the site may support two units, do not let the first block the second by accident. Review access, utilities and outdoor space for the whole lot.
The detached, attached and conversion guides provide work checklists.
What permits and design work belong in the quote?
Ask who confirms zoning and prepares the site plan. Assign plans for the current building, new unit, structure, energy and trades. The quote should name the person who answers City comments.
If a company suggests a standard or prefab plan, confirm its code basis, change limits and Burien review path. A design marketed across Washington is not property approval.
Use the design and permits guide to assign each task.
What utilities and external work need a separate line?
Map sewer, water, power and drainage. Ask whether current services have capacity and whether trenches cross paving, trees or plants. Add street work, hauling, erosion control and property repairs when needed.
A 1,000-square-foot cap does not mean site costs are capped. The utilities and site-work guide helps prevent external work from becoming a late allowance.
How much does a Burien ADU cost?
No citywide price applies to every unit type and lot. Use the Seattle-area cost guide as a budget schedule. Then replace broad ranges with the Burien site and design.
Separate site checks, survey, design, engineering and permits. Add demolition, access, foundation, construction, utilities, finishes and repairs. Keep money for surprises. Require written allowances and owner-bought item lists from every company.
How should Burien builders be compared?
Check the legal builder and registration through Washington L&I. Ask for recent Burien or south King County ADUs and the permit office for each. Confirm that the company on the quote did the work shown.
Give companies the same site facts, plan basis and finish schedule. Use the builder comparison guide for registration, project proof, design, permits, utilities, payment, schedule assumptions and written warranty terms.
Plan the lot for the long term
If the lot may support two ADUs, show the first and a possible later unit on one sketch. Check whether the first footprint, trench, power equipment or sewer route blocks the second. Add outdoor space and work access. The owner need not build both but should see the trade-off.
Also record current legal units and structures. Confirm with Burien how the planned layout is counted and which size or existing-space provisions apply to this parcel.
What should a Burien bid packet contain?
Include current parcel and zoning details, site plan or survey, selected ADU concept, access and tree notes, service routes and a finish schedule. Require every bidder to include the same design, engineering, permit, site, utility and repairs after the work duties.
Ask who answers City comments and plans utility or street work. Mark each unknown and the review needed to price it. This keeps a simple size comparison from hiding a difficult site or missing utility work.
What should be checked before work starts?
Compare the issued Burien permit set with the contract drawings and allowances. Confirm the legal contractor, current L&I registration and proof of insurance. Record permit conditions, inspection milestones, utility approvals and any work that remains owner-direct.
Give the site supervisor the same approved tree, drainage, access and service details used for pricing.
Frequently asked questions
Does Burien allow two ADUs on every lot?
The current code describes a maximum of two. But the site’s zoning, current development and other standards still control.
Is every Burien ADU limited to exactly 1,000 square feet?
The code generally uses 1,000 square feet and describes a limited existing-space exception. Confirm current eligibility with the City.
Can a Seattle pre-approved plan be used in Burien?
Do not assume so. Confirm plan rights, code review and the Burien permit path.
Does this site guarantee a Burien contractor?
No. Company coverage and capacity are checked separately.