Direct Answer
In Seattle, septic system installation & replacement work generally requires a permit when the project exceeds $500 or involves system replacements. Your licensed contractor should pull the permit — if they ask you to pull it yourself, that's a red flag. Unpermitted work can cause problems when selling your home.
Full Explanation
Seattle follows WA state building codes administered by the local building department. Permit fees vary by project value. All inspections must be scheduled through the Seattle building department. Keep all permit documentation — required for home resale disclosure.
Local Factors in Seattle
📍WA permit threshold: $500
📍Seattle building department issues local permits
📍Sales tax on materials: 9.5-10.5%
📍Permit records are public and transfer with the home