"We hired MNBE to build our ADU in Bellevue, and the entire experience was amazing. They handled everything from foundations and framing to kitchen, siding, windows and HVAC."
Zena Heywood
Bellevue, WA · Attached ADU
FIVE-STAR RATEDRATED ON GOOGLE
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Sumner & Lake Tapps ADU & DADU rules, in plain English
Lake Tapps lots fall under different jurisdictions. Here are the ADU rules for the City of Sumner and unincorporated Pierce County. Written by MNBE founder Aharon Ben Elisha. Checked October 28, 2026.
Sumner: SMC 18.12.030 Pierce County: PCC 18A.37.120 Check the jurisdiction first
The Update
What changed in Sumner & Lake Tapps.
Most lots around Lake Tapps are in unincorporated Pierce County, not in Sumner; some are in Bonney Lake or Auburn (Cascade Water Alliance). So the first step is the parcel's jurisdiction. This guide covers the two most common: the City of Sumner and unincorporated Pierce County.
Sumner's ADU rules sit in SMC 18.12.030, last amended by Ordinance 2964 in July 2026. Pierce County's sit in PCC 18A.37.120, updated by Ordinance 2025-516s (effective June 30, 2025) and Ordinance 2026-523s (effective August 1, 2026).
What we are building at Lake Tapps
Our two-story home at Lake Tapps is in permitting now. See the plan on the Lake Tapps home page.
Rules for other cities are in our ADU rules by city guide.
Sumner & Lake Tapps · SMC 18.12.030 · PCC 18A.37.120
Sumner & Lake Tapps' ADU rules, by the numbers.
The four numbers homeowners ask about first. Check them against your lot with a feasibility study →
2
ADUs per lot
In Sumner, and inside Pierce County's urban growth area.
1,000sq ft
Size cap
Sumner and urban Pierce County. Rural Pierce County: 1,250.
24feet
Sumner DADU height
Or the house's height, if lower.
1
Parking space
Per ADU, except near a major transit stop.
The Code
Sumner & Lake Tapps ADU rules, line by line.
Two jurisdictions in one table. Each row says which one it covers.
| Rule | What Sumner & Lake Tapps allows | Source |
|---|---|---|
| Sumner: ADUs per lot | Two, attached or detached, with the one house. None on a lot smaller than the zone's minimum lot size. | SMC 18.12.030 |
| Sumner: size and height | 1,000 sq ft, not counting a garage. DADU height: 24 feet, or the house's height if lower. Upper-floor living-room and dining windows face into the site. | SMC 18.12.030 |
| Sumner: setbacks | The house's setbacks apply. A DADU may sit on the lot line at an alley, and an ADU 18 feet or lower can be 15 feet from the rear and 7.5 feet from the side. | SMC 18.12.030 |
| Sumner: parking | One space per ADU, none within half a mile of the Sumner transit station. | SMC 18.12.030 |
| Sumner: ownership | Sumner's code ties separate ownership to subdividing the ADU onto its own conforming lot. State law separately protects condominium sales. | SMC 18.12.030 |
| Sumner: existing structures | A legally built accessory structure can be converted and expanded up to 1,000 sq ft, without added encroachment or coverage. | SMC 18.12.030 |
| Pierce County: ADUs per lot | Inside the urban growth area: two, in any combination. Outside it: one. | PCC 18A.37.120 |
| Pierce County: size | 1,000 sq ft inside the urban growth area, 1,250 sq ft in rural areas, measured as interior living area; a garage doesn't count. | PCC 18A.37.120 |
| Pierce County: height | No taller than the house, or one story taller when built over a detached garage, and never capped below 24 feet. | PCC 18A.37.120 |
| Pierce County: setbacks | A new DADU stays out of the required yards and no closer to the front than the house, with reduced side and rear setbacks in some urban cases. | PCC 18A.37.120 |
| Pierce County: parking | One space per ADU, none within half a mile of a major transit stop. | PCC 18A.35.040 |
| Owner occupancy | Not required in Sumner or Pierce County. | RCW 36.70A.681 |
| Shoreline | At Lake Tapps, shoreline rules (Pierce County Title 18S) and critical area rules apply, and work near the lake may need Cascade Water Alliance approval. | Cascade Water Alliance |
Checked October 28, 2026. Sources: Sumner SMC Chapter 18.12, PCC 18A.37.120, PCC 18A.35.040, Cascade Water Alliance Lake Tapps plan and RCW 36.70A.681. Lake Tapps zoning is checked parcel by parcel. A plain-English summary, not legal advice. The code governs, and we confirm it for your lot.
Your Lot
How we check a Sumner & Lake Tapps lot for an ADU.
The code sets the outer limits. Your lot sets the real ones. This is the order we work in during the free site visit and feasibility.
01
Jurisdiction
We confirm whether the parcel is in Sumner, Bonney Lake, Auburn or unincorporated Pierce County, and its zone.
Zoning
02
Shoreline and critical areas
Near the lake we check the shoreline rules, critical areas and any Cascade Water Alliance approval.
Shoreline
03
Fit the footprint
We test size, height, setbacks and coverage against your house, and whether a garage can be converted.
Footprint
04
Sewer or septic
We confirm sewer availability or the septic approval the ADU needs.
Utilities
05
Design and permit
We draw the plans in house, submit to the right jurisdiction and carry the project through inspections.
Review
Reviews
What Seattle homeowners say about building with MNBE.
Verified five star reviews from owners we guided through ADU feasibility, permitting, and construction.
"We hired MNBE for a full renovation of our 100 year old home and the results exceeded expectations, structural upgrades, new insulation, a luxury bathroom, a high end kitchen, a new roof and mini split AC."
Dave Gierok
Redmond, WA · DADU
"My mom hired MNBE Construction for her two-bedroom DADU in Seattle, and watching the process up close was impressive. They did it all: design, architectural plans, the building permit, and the full construction. … The communication was excellent and there were never any surprises."
Maryam Z.
White Center, WA · ADU
Schedule Free Estimate
FIVE-STAR RATEDRATED ON GOOGLE
LICENSED · BONDED& FULLY INSURED
FAQs · Sumner & Lake Tapps ADU rules
Sumner & Lake Tapps ADU questions we hear on site visits.
Short answers from the code. For your exact lot, call us or book the free site visit.
Mostly not. Most Lake Tapps lots are in unincorporated Pierce County; some are in Bonney Lake or Auburn. We confirm the jurisdiction for each parcel first.
Two, attached or detached, with the house, on a lot that meets the zone's minimum lot size.
1,000 square feet inside the urban growth area and 1,250 square feet in rural areas, not counting a garage.
In Sumner, 24 feet or the house's height if lower. In Pierce County, no taller than the house, or one story taller over a detached garage, and never capped below 24 feet.
Sumner and Pierce County ask for one space per ADU, except within half a mile of a major transit stop or, in Sumner, the transit station.
Contact Us · Free Estimate
Tell us about your project.
We'll confirm your jurisdiction, check its ADU code and get back to you within one business day with a clear next step.
Contact information
Thank you for considering MNBE. Thank you for considering MNBE. Tell us your address and we will tell you, in writing, what your jurisdiction's code allows on your lot. We respond within one business day, Monday through Saturday.
(206) 637 0044
info@mnbe-wa.com
2014 Fairview Ave Unit 2308, Seattle, WA 98121