What Is a Septic Rating in Snohomish County?
In Snohomish County, a “septic rating” refers to the number of bedrooms a septic system was originally designed and approved to support.
The official term is the system’s septic design capacity.
It is determined when the septic system is permitted and installed — and it is on file with the county.
It has nothing to do with the current condition of the system.
What a Septic Rating Actually Means
Snohomish County approves septic systems based on expected wastewater usage.
Bedrooms are used as the standard measurement of wastewater flow.
You may see language like:
- “Septic approved for 3 bedrooms”
- “Designed for 4-bedroom capacity”
- “2-bedroom septic system”
This number is a legal limit.
It defines how many bedrooms the property is allowed to serve — regardless of how many rooms exist in the house.
Why Bedrooms Matter
More bedrooms = more occupants = more water usage.
Septic systems are engineered to handle a specific daily flow. That flow is calculated using bedroom count — not square footage.
If the system was designed for 2 bedrooms, the home is legally treated as a 2-bedroom septic property, even if:
- The home has 4 physical bedrooms
- The septic system passes inspection
- The system is functioning properly
The rating controls legal bedroom count.
Why This Affects Buying and Selling
This becomes critical during:
- Appraisals
- Financing approval
- MLS marketing
- Disclosure review
Example:
A home has:
- 4 physical bedrooms
- A septic system rated for 2 bedrooms
- A clean septic inspection
For lending and valuation purposes, that property is considered a 2-bedroom home.
It cannot be marketed, appraised, or financed as a 4-bedroom property without a septic system upgrade approved by the county.
Common Problems This Creates
- Financing delays
- Appraisal reductions
- Disclosure issues
- Value disputes
- Buyer confusion
This is one of the most misunderstood issues in Snohomish County real estate transactions.
Inspection vs. Rating (Important Distinction)
A septic inspection checks whether the system is functioning properly.
A septic rating defines how many bedrooms the system is legally allowed to serve.
They are completely different.
You can have:
- A perfectly functioning septic system
- That is legally limited to fewer bedrooms than the house contains
Condition does not change design capacity.
Where Do You Find the Septic Rating?
The septic rating (design capacity) can be found in:
- The original septic permit
- The septic as-built drawing
- Snohomish County Health Department records
Official records are available through:
Snohomish County As-Built Records Search
https://www.snohd.org/159/As-Built-Records
If records are not available online, a formal records request may be required.
Can You Upgrade a Septic Rating?
Sometimes.
Upgrading requires:
- County approval
- Soil evaluation
- Drainfield capacity review
- Possibly a new septic design
In many cases, increasing bedroom capacity means installing a larger or new septic system.
It is not automatic.
Bottom Line
A septic rating in Snohomish County controls how a home can be:
- Marketed
- Valued
- Appraised
- Financed
It is a legal design limitation — not a performance score.
Before buying or selling a septic property, verify the system’s approved bedroom capacity early to avoid surprises during inspection and underwriting.
FAQ
What does septic rating mean in Snohomish County?
It refers to the septic system’s approved bedroom design capacity on file with the county.
Where do you find the septic rating?
In Snohomish County Health Department records, the original septic permit, or the septic as-built drawing.
Can a home have more bedrooms than the septic rating?
Yes, but it must be marketed, appraised, and financed based on the septic rating unless the system is upgraded.
Does a septic inspection change the rating?
No. Inspection evaluates condition; rating defines legal design capacity.
Can you upgrade a septic rating?
Sometimes. It requires county approval and often a redesigned or expanded septic system.