ADU Plans and Permits in Pierce and King County
Start with your address
Backyard cottages, garage conversions, and units over the garage. We check your lot, draw the plans, and take the permit through the city or county.
A lot of people want an ADU for a parent, a grown kid, a home office, or some rent to help with the mortgage. The first question is always the same: what will my lot actually allow?
Washington changed its ADU laws, and most cities around here have rewritten their codes. That's mostly good news. But the rules in Puyallup don't match Bonney Lake's, and unincorporated Pierce County has its own. Size caps, setbacks, height, parking, and utility connections all change from place to place.
So before we draw anything, we look up your parcel. We check zoning, setbacks, slopes, easements, critical areas, and where sewer or septic, water, and power would connect. If something on the lot is a deal-breaker, you hear about it before you pay for design.
What we draw
Detached backyard cottage (DADU): a small house on its own foundation
Garage conversion: turning an existing garage into a unit
Unit over a garage: new or existing garage with living space above
Attached or basement unit: an addition, a basement, or a lower level with its own entry
What's in the permit set
Site plan with setbacks, utilities, and access
Floor plans, elevations, and sections
Construction notes and details the reviewer expects to see
Washington energy code (WSEC-R) forms
Structural drawings and calcs from Dow Engineering PLLC, when the project needs them
We run the permit, too
Drawing the plans is half the job. The other half is getting them through review. We put the application together, upload it to the portal, keep an eye on it, and write the answers when the reviewer sends comments. Most ADU delays come from a missing dimension or a form that doesn't match the plans, and that's the stuff we're careful about.
Already have a correction letter? Send it over.
When the structure needs an engineer
Lots of ADUs can be built to the standard residential code with no engineer. Some can't: tall walls, big window openings, a unit over a garage, a steep lot, or an old garage slab being turned into a floor. When the city wants a stamp, we hand that piece to Dow Engineering PLLC. They're in the same office in Sumner, so the drawings and the calcs match.
The air test before final
New ADUs usually need a blower door air leakage test before final inspection. Book it early so it doesn't hold up your occupancy. WA Blower Door is our sister company and does these air leakage tests around Puget Sound.
Where we work
Sumner, Puyallup, Bonney Lake, Tacoma, Auburn, Kent, unincorporated Pierce County, and King County cities, Seattle included.
Got something already built without a permit, like a converted garage or an old cottage? See Already Built? Permits for Work Done Without One.
ADU questions we get a lot
Can I put an ADU on my lot?
Most likely, if you're inside a city or an urban area of the county. State law now has most of those places allowing ADUs, and often two per lot. Rural lots, septic systems, steep slopes, and wetlands can change that. Send us your address and we'll look it up.
Do I need an architect?
Usually not. In Washington, most houses and ADUs can be drawn by a building designer. If the structure needs an engineer, we bring in Dow Engineering PLLC.
How long does the permit take?
It depends on the city and how complete the application is. Some places move quickly. Others take months. We'll give you a straight answer for your jurisdiction when we start.
What does it cost?
Every lot is different. We'll look at your address and what you want to build, then give you a clear price for the plans and permit work.
Can I build it myself?
Yes. A lot of homeowners pull the permit as owner-builders. We can help you plan the job and the inspections.
Can you turn my garage into an ADU?
Often, yes. The slab, the ceiling height, insulation, and egress windows are the usual hang-ups. We check those first.
Do you build ADUs?
No. We draw the plans and run the permit. You or your contractor build it.
Will it need a blower door test?
Almost always, for a new unit. WA Blower Door can schedule it.
Thinking about an ADU? Start with your address.
Send us the address, a few photos of the yard, and what you have in mind. A sketch on a napkin is fine. Call (253) 799-0606 or email office@buildsherpas.com.