What Permits Are Required for a DADU in King, Snohomish, or Pierce Counties?

Victor K • August 2, 2025

Before contracting for an ADU in Seattle, it is important to know the different kinds of permits and the processes involved. Since it usually ends in a legal battle, it becomes a struggle costing you money, time, and reputation in the market. You must also fully understand that some of the permit laws are similar for all counties but some are county-specific which must be catered for by the commercial subcontractor Seattle. Many instances in the past have involved the wrong permit process initiation by the commercial project management Seattle causing later headaches. Let us dive into some of the steps you must take as a commercial construction subcontractor Seattle to ensure that your legal aspect is as good as your construction practice.

Major Permit Requirements for all DADUs in Seattle

Regardless of the county or area in Seattle, some permit laws and regulations are the same for all. This is why a smart commercial subcontractor Seattle needs to be smarter regarding the location of the DADU. The permit has to be applied to the right authorities and followed up in a correct manner based on location. First, let us see some of the generic permit requirements in Seattle.

Construction Permit

This is the main permit that involves the main structure of the DADU. The commercial construction subcontractor Seattle has to provide site plans, floor plans, design drawings of both elevation & cross section, energy code forms and certain engineer approvals if the designs are custom-built.

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Zoning Permit

The second most important permit is the zoning and land use that needs to be filed by a commercial building services Washington. This review is a baseline for lot size and coverage, height, changes in current structure, parking requirements and street access.

Utility Connection Permit

Since a DADU is a separate entity from the main structure of the property, separate utility needs to be provided. Commercial subcontractor Seattle has to file for water, sewer, electrical permits which might include lateral lines, side sewer connections, electrical paneling and storm drain water compliance.

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Trade Permit

Some counties require separate permits for electrical, plumbing and mechanical systems. However, some counties allow bundling of these permits with the main permits explained above. Therefore, a building subcontractor Washington with experience and proper knowledge will save you time and money by applying for the correct permits with the exact documentation required.

Now, coming to the three counties where these questions are asked the most!

King County

· SDCI manages all DADU permits and offers a fast track for pre-completed applications. This is something United Seattle has expertise in which helps in shortening the review time.

· The energy code becomes strict in King County, where United Seattle's groundbreaking AeroBarrier technology comes into play.

· Tree protection plans are required for plantations near the construction site. This is one of the most overlooked areas in the permit application process.

· Sewer capacity charges apply for new dwelling units, and those must be reviewed by the King County Wastewater Division.

Snohomish County

· PDS issues all the permits with a special septic review for non-connected sewer systems.

· Design reviews are required in some cities to match the architectural heritage.

· Some neighborhoods do not approve of second driveways and therefore, it needs to be catered to in the design phase.

· WUI zones may ask for fire-resistant construction material which again has to be pre-planned

Pierce County

· Pierce County Planning & Public Works approves the DADU permits with additional strictness in the hilly neighborhoods.

· Fire department clearance is additionally required for emergency access

· Stormwater drainage reviews are more rigorous in Pierce County than in other areas.

· Utility coordination may require working with Tacoma Power and Tacoma Public Utilities, which have their own timelines and application processes separate from city permits.

Where Does United Seattle Come In?

Working with a commercial subcontractor Seattle who understands the inspection schedule is key to avoiding work stoppages. This is especially where the expertise of United Seattle in the DADU construction area comes in. They assist you with permit-ready drawings, utility permit coordination, advising on local code variations, sequencing the whole process and being there for you every step of the way. The delay in time for the permit process can be used as an asset if the commercial construction subcontractor Seattle is an experienced company with loads of DADU construction under their belt.

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