Tri-Cities ADU Regulations: Pasco, Kennewick & Richland Permit Guide

If you're considering building an Accessory Dwelling Unit (ADU) in the Tri-Cities area, understanding local regulations is your first critical step. While Washington State has made it easier to build ADUs with recent legislation, each city in our region—Pasco, Kennewick, and Richland—has its own specific requirements that can significantly impact your project.

This comprehensive guide breaks down exactly what you need to know for each Tri-Cities municipality, from size limits and parking requirements to owner-occupancy rules and permit processes. Whether you're planning a backyard cottage for aging parents, a rental income property, or flexible living space, you'll find the specific regulations that apply to your property.

Understanding Washington State's ADU Laws

Before diving into city-specific regulations, it's important to understand the state framework. Washington's Growth Management Act (GMA) now requires cities in urban growth areas to permit ADUs, making our state one of the most ADU-friendly in the nation.

Key state-level requirements include:

• At least two ADUs must be allowed per residential lot (attached, detached, or combination)
• Minimum size cannot be restricted below 1,000 square feet
• No owner-occupancy requirements for properties within urban growth areas
• ADUs must follow the same setback and dimensional standards as the primary residence
• Cities cannot require street improvements as a condition for ADU permits

These changes, which took effect in 2024, represent a significant shift designed to address Washington's housing shortage. However, local municipalities can still enforce additional requirements within these guidelines.

ADU Regulations in Pasco, Washington

Pasco adopted comprehensive ADU regulations under PMC Chapter 25.161 following Washington's 2019 legislative changes. The city successfully secured grant funding to implement these regulations and has created one of the more progressive ADU frameworks in the Tri-Cities.

What's Allowed in Pasco

• One attached OR one detached ADU per property with a single-family dwelling
• Both internal conversions and new construction permitted
• ADUs allowed in all residential zones

Size Requirements

Detached ADUs: Maximum 800 square feet, with potential for larger units based on lot size and specific conditions

Attached ADUs: Up to 50% of the primary dwelling's living area

Height & Setback Standards

• Detached ADUs generally limited to 20 feet in height
• Must meet fire separation requirements per city building code
• Fire sprinkler system required if ADU exceeds maximum distance to fire hydrant

Occupancy & Use Restrictions

Long-term residential use only: ADUs must be used for long-term residential purposes. Residents must live in the ADU for longer than 180 days per calendar year. Short-term rentals and vacation rentals are prohibited.

No owner-occupancy requirement: Pasco does not generally require the property owner to live on-site, though this may vary depending on specific zoning rules.

Parking Requirements

One additional parking space is generally required for ADUs, with potential exceptions based on proximity to public transit.

Utility Connections

Sanitary sewer and surface water services must be built and permitted according to Pasco standard specifications. Right-of-way improvements are only required to address impacts created by the ADU development itself.

ADU Regulations in Kennewick, Washington

Kennewick permits ADUs in most residential zones and has established regulations designed to balance housing expansion with neighborhood character. The city allows both attached and detached units with specific size limitations.

What's Allowed in Kennewick

• Both attached and detached ADUs permitted
• Allowed in most residential zones, including single-family and multi-family areas
• Internal conversions, additions, and new construction all allowed

Size Requirements

Detached ADUs: Maximum 1,100 square feet (can be larger depending on lot size). Historically, detached ADUs on lots under 10,000 square feet were prohibited, but newer state regulations may have changed this.

Attached ADUs: Up to 50% of the primary dwelling's living area

Height & Design Standards

• ADUs generally limited to one story
• Height must not exceed that of the primary dwelling
• Must meet all building, fire, and health safety codes

Parking Requirements

One additional off-street parking space required for ADUs. This requirement can be waived if the ADU is within half a mile of public transit.

Owner-Occupancy Requirements

The property owner must reside in either the primary dwelling or the ADU. However, recent state legislation may override local owner-occupancy requirements for properties in urban growth areas.

Approval Process

ADUs that meet zoning and building requirements are subject to a streamlined administrative approval process, making the permitting timeline more predictable than discretionary review.

ADU Regulations in Richland, Washington

Richland refers to ADUs as "accessory apartments" in its municipal code (RMC 23.42). The city permits one accessory apartment per single-family dwelling in all single-family zones, with specific requirements that property owners should understand before beginning their project.

What's Allowed in Richland

• One accessory apartment per single-family dwelling
• Allowed as permitted uses in all single-family zones
• Can be added to existing residence, built adjacent, or constructed with new home
• A lot with two or more primary dwellings cannot have an ADU

Size Requirements

Maximum: Cannot exceed 40% of the dwelling's total floor area AND cannot exceed 800 square feet of interior floor space

Minimum: Not less than 220 square feet

Note: Richland's 800 square foot maximum is lower than the state-mandated 1,000 square foot minimum for new regulations. Property owners should consult with the city's Community Development department to understand how recent state legislation affects these limits.

Unit Requirements

• Each accessory apartment must have a kitchen and bathroom
• Cannot contain more than two bedrooms
• Must comply with all building, fire, and health safety codes
• Recreational vehicles cannot be used as accessory apartments

Owner-Occupancy Requirements

Traditionally, Richland's code includes owner-occupancy requirements. However, recent Washington State legislation prohibits owner-occupancy requirements within urban growth areas, which may supersede local regulations. Confirm current requirements with the city's Development Services department.

Quick Comparison: Tri-Cities ADU Regulations

City: Pasco

• Max Size (Detached): 800 sq ft (potentially larger)
• Max Size (Attached): 50% of primary dwelling
• Max Height: 20 feet (detached)
• Parking: One space required
• Owner-Occupancy: Not required
• Short-Term Rentals: Prohibited (must be 180+ days/year)

City: Kennewick

• Max Size (Detached): 1,100 sq ft
• Max Size (Attached): 50% of primary dwelling
• Max Height: Cannot exceed primary dwelling
• Parking: One space (waived if within 0.5 mile of transit)
• Owner-Occupancy: Required (may be superseded by state law)
• Approval: Streamlined administrative process

City: Richland

• Max Size: 40% of primary dwelling AND max 800 sq ft
• Min Size: 220 sq ft
• Max Bedrooms: Two
• Owner-Occupancy: Check with city (state law may supersede)
• Note: Size limits may conflict with state minimums

The Tri-Cities ADU Permitting Process

While specific requirements vary by city, the general ADU permitting process in the Tri-Cities follows a similar pattern:

Step 1: Property Assessment

• Verify your property is in a zone that permits ADUs
• Check lot size requirements for your city
• Confirm setback requirements and available space
• Review any HOA restrictions (if applicable)

Step 2: Design & Planning

• Work with an architect or designer familiar with ADU regulations
• Ensure design meets city-specific size and height limits
• Plan for utility connections (water, sewer, electrical)
• Address parking requirements in your site plan

Step 3: Permit Application

• Submit building permit application to your city's building department
• Include detailed site plans, floor plans, and elevations
• Pay applicable permit fees
• Await administrative review (streamlined in most cases)

Step 4: Construction

• Hire licensed contractors familiar with ADU construction
• Schedule required inspections at various stages
• Ensure compliance with all building, fire, and safety codes
• Complete final inspection and obtain certificate of occupancy

Cost Considerations for Tri-Cities ADUs

Building an ADU in the Tri-Cities is a significant investment. Here's what to budget for:

Typical Construction Costs

• Detached ADU: $150,000 – $300,000+ depending on size and finishes
• Garage Conversion: $80,000 – $150,000
• Attached ADU: $100,000 – $200,000

Additional Expenses

• Permit fees: $2,000 – $5,000+
• Utility connections: $5,000 – $15,000
• Architectural/design fees: $3,000 – $10,000
• Impact fees (vary by city, may be reduced for ADUs)
• Landscaping and site work: $5,000 – $20,000

Financing Your ADU

• Home Equity Line of Credit (HELOC)
• Cash-out refinance
• Construction loans
• Personal loans or savings
• Check with local banks and credit unions for ADU-specific loan programs

Why Work With Tiny Cottage Builders for Your Tri-Cities ADU

Navigating ADU regulations across different Tri-Cities municipalities can be complex. That's where local expertise makes all the difference. At Tiny Cottage Builders, we specialize in ADU construction and home remodeling throughout Pasco, Kennewick, and Richland.

Our team understands the specific requirements for each city and can guide you through:

• City-specific design that meets all local regulations
• Permit application and approval process
• Design options that maximize your property's potential
• Quality construction with attention to Tri-Cities climate considerations
• Coordination with utility providers and city inspectors

Important Considerations Before Building

Tri-Cities Climate Factors

The Tri-Cities experiences hot, dry summers and cold winters. Your ADU design should account for:

• High-efficiency HVAC systems (consider mini-splits)
• Proper insulation for temperature extremes
• Energy-efficient windows and doors
• Adequate shade and ventilation for summer cooling

HOA Restrictions

If your property is in an HOA, review your covenants, conditions, and restrictions (CC&Rs) carefully. While state law supports ADUs, some HOAs may have additional design requirements or approval processes. We can help you navigate these requirements.

Timeline Expectations

• Design phase: 1-3 months
• Permit approval: 2-6 weeks (streamlined administrative review)
• Construction: 4-8 months depending on complexity
• Total project timeline: 8-12 months on average

Ready to Start Your Tri-Cities ADU Project?

Building an ADU in the Tri-Cities is more accessible than ever, thanks to supportive state legislation and local regulations. Whether you're looking to create rental income, accommodate family members, or increase your property value, an ADU can be an excellent investment.

The key to a successful ADU project is understanding the specific regulations for your city and working with experienced local builders who can navigate the process efficiently. Each city—Pasco, Kennewick, and Richland—has unique requirements, and staying compliant while maximizing your investment requires local expertise.

At Tiny Cottage Builders, we've helped numerous Tri-Cities homeowners successfully complete their ADU projects. We handle everything from initial design through final inspection, ensuring your project meets all local requirements while staying on schedule and within budget.

Contact us today for a free consultation to discuss your ADU project. We'll review your property, explain the specific requirements for your city, and help you create a plan that brings your vision to life.

Frequently Asked Questions

Do I need to live on the property if I build an ADU in the Tri-Cities?

It depends on the city and recent state legislation. Pasco generally does not require owner-occupancy. Kennewick traditionally required it, but this may be superseded by state law for properties in urban growth areas. Richland's requirements should be confirmed with the city. Washington State law prohibits owner-occupancy requirements in urban growth areas, which may override local restrictions.

Can I use my ADU as a short-term rental (Airbnb)?

In Pasco, no—ADUs must be used for long-term residential purposes (180+ days per year). Kennewick and Richland regulations should be confirmed with each city's planning department. Short-term rental regulations vary significantly by municipality and may require additional permits.

How long does it take to get an ADU permit in the Tri-Cities?

Most Tri-Cities municipalities offer streamlined administrative approval for ADUs that meet code requirements. This typically takes 2-6 weeks, though complex projects or those requiring variances may take longer. Working with experienced builders who understand local requirements can help expedite the process.

What's the difference between attached and detached ADUs?

An attached ADU shares at least one wall with the primary residence and may share utilities. A detached ADU is a separate structure on the same property. Size limits and requirements can vary between the two types depending on your city. Detached ADUs often provide more privacy but may cost more due to separate utility connections and foundation work.

Will building an ADU increase my property taxes?

Yes, adding an ADU will likely increase your property's assessed value, which typically results in higher property taxes. However, the rental income or increased property value often offsets this increase. Consult with your county assessor's office for specific guidance on how ADUs are assessed in your area.

Can I convert my existing garage into an ADU?

Yes, garage conversions are permitted in all three Tri-Cities municipalities. This can be a more cost-effective option than building a new structure. However, you'll need to address parking requirements (which vary by city) and ensure the converted space meets all building codes for residential occupancy, including proper insulation, heating, and ventilation.

Important Note: ADU regulations are subject to change as cities update their codes to comply with evolving state legislation. Always verify current requirements with your city's planning or development services department before beginning your project. This guide is current as of December 2024 but should not be considered legal advice. For the most up-to-date information, contact:

• City of Pasco Community and Economic Development: (509) 545-3441
• City of Kennewick Community Planning: (509) 585-4280
• City of Richland Development Services: (509) 942-7630

Ready to explore your ADU options? Contact Tiny Cottage Builders today for a free consultation and let us help you navigate the Tri-Cities ADU process from concept to completion.