Tacoma ADU Basics for Buyers: What to Check Before You Buy
Important Note Before We Start
This article is for general educational purposes only.
If you are already under contract, your own real estate agent, lender, and the City of Tacoma must guide you, as Washington law does not allow outside agents to advise on another agent’s active transaction.
What follows is a practical overview of what buyers typically check when considering a home with an ADU in Tacoma.
1. Why ADUs Are So Popular With Tacoma Buyers
Accessory Dwelling Units (ADUs) are attractive because they can offer:
Rental income
Multigenerational living
Guest or office space
Long-term flexibility
In Tacoma, interest in ADUs has grown as buyers look for creative ways to offset housing costs — but not every ADU is created equal.
2. What Counts as an ADU in Tacoma?
In Tacoma, an ADU is a secondary living unit on a residential property.
Common types include:
Detached backyard cottages
Converted garages
Basement or above-garage units
The key distinction is whether the unit is legally recognized by the city — not just whether it functions like a separate space.
3. Permitted vs Unpermitted ADUs: The First Thing to Verify
One of the most important checks for buyers is whether the ADU was:
Properly permitted
Built to code
Finaled by the city
An ADU can look great and still be unpermitted.
If you’re unfamiliar with how unpermitted work affects buyers, this breakdown helps:
Buying a Home With Unpermitted Work in Washington: A Reality Check for Buyers
4. Zoning and Lot Requirements in Tacoma
Not all Tacoma lots qualify for ADUs.
Buyers should understand that ADU eligibility depends on:
Zoning designation
Lot size
Setbacks
Utility access
Zoning rules can change, so buyers should never assume an ADU is allowed just because another property nearby has one.
5. Utilities: Separate or Shared?
Buyers often overlook utilities when evaluating an ADU.
Important questions include:
Are water, sewer, and electric shared or separate?
Are meters independent?
Are utilities sized appropriately?
Utility configuration can affect:
Monthly costs
Rental feasibility
Future resale
6. Financing and Appraisal Considerations
Not all lenders treat ADUs the same.
Potential issues include:
Rental income not counted
ADU square footage excluded
Appraisal value adjustments
Unpermitted or non-conforming ADUs may not add value at all from a lender’s perspective.
This ties directly into appraisal outcomes:
Appraisal Contingency in Washington: What It Is and Your Options If the Appraisal Comes in Low
7. Disclosure Expectations for ADUs
Washington sellers must disclose known material facts, including:
Whether an ADU is permitted
Known code or permit issues
Estate sellers or long-time owners may legitimately answer “don’t know,” but known information must be disclosed.
Disclosures are explained in detail here:
WA Form 17 Seller Disclosure: A Simple, Complete Guide for Washington Sellers
8. Rental Reality vs Buyer Assumptions
Many buyers assume:
ADU = guaranteed rental income
In reality, rental legality depends on:
City rules
Permit status
Owner-occupancy requirements
Utility setup
An ADU’s existence does not automatically mean it can be rented.
9. ADUs and Inspection Findings
Inspectors evaluate:
Safety
Functionality
Visible defects
They do not determine legality.
A clean inspection does not confirm the ADU is legal — which is why buyers must separate condition from compliance.
10. Resale Considerations Buyers Should Think About Now
Even if an ADU works for you today, consider:
Future buyer financing limits
Appraisal treatment
Permit questions during resale
ADUs can be an asset — or a friction point — depending on how they’re documented.
11. ADUs When Selling and Buying at the Same Time
For move-up buyers:
Sale proceeds
Financing approval
Appraisal outcomes
…can all be affected by an ADU on either property.
Planning matters:
The Step-by-Step Move-Up Buyer Plan: How to Sell Your Current Home & Buy Your Next One Smoothly in Washington (2025 Guide)
12. The Big Picture: ADUs Are Powerful — When Done Right
ADUs can create flexibility, income potential, and long-term value — but only when buyers understand what they’re actually buying.
Checking:
Permit status
Zoning
Utilities
Financing impacts
…before writing an offer helps prevent expensive surprises later.
And once again, if you are already under contract, your own agent, lender, and the City of Tacoma must guide your next steps.
If you’re considering buying in Tacoma and want to understand ADU realities before writing an offer, learning these basics early can save a lot of stress down the road.
Written by: Lani Fisher — Washington Realtor Helping Everyday Buyers & Sellers With Confidence