Mason County, WA Accessory Structures: Shed & Carport Rules (2026)
Shed permit rules in Mason County, WA, also referred to as storage shed, backyard shed, or accessory building regulations, set size limits, setbacks, and when a building permit is required.
Key Facts
- Size limit for exemption
- 576 sq ft or less
- Height limit
- 10 feet wall height maximum
- Setback
- 10 feet from other structures
- Paperwork required
- Affidavit of exemption recorded on title
- Still required
- Plumbing/mechanical permits; no floodway exemption
Summary
A storage shed in unincorporated Mason County skips the building permit only if it is single-story, five hundred seventy-six square feet or smaller, no taller than ten feet at the wall, and set back at least ten feet from other structures, per Mason County Code Section 14.08.031(2). Larger or taller sheds need a permit.
Sections [A]105.2 and R 105.2 of the International Building Code and International Residential Code are adopted herein by reference and supplemented with the following: ... (2)Storage (Non-Agricultural) Buildings: Single-story buildings or structures used for the storage of belongings, not designed for human habitation, and not used for remunerative purposes. These structures shall not be a place of human habitation or a place of employment, nor shall it be a place used by the public. Storage buildings shall be exempt when five hundred seventy-six square feet or less with a wall height not to exceed ten feet and shall be setback ten feet from all other structures.
Full Breakdown
Mason County Code Section 14.08.031, adopting and supplementing IBC/IRC Section 105.2, exempts a single-story storage building from the building permit requirement when it is used only for storing belongings, not designed for human habitation, and not used for a remunerative purpose, is not a place of employment or a place used by the public, is five hundred seventy-six square feet or less, has a wall height no greater than ten feet, and sits at least ten feet back from every other structure on the lot.
A separate exemption at subsection (1) covers single-story agricultural buildings up to eight hundred sixty-four square feet with a wall height up to sixteen feet, also with a ten-foot setback, though that exemption never applies to a structure used to grow or produce medical or recreational cannabis, which stays subject to Chapter 17.17. To actually claim either exemption, subsection (4) requires the owner to record an affidavit of exemption on title certifying the structure meets the size and setback description, confirming it is not in a critical area unless it complies with the Chapter 8.52 resource ordinance, confirming it meets Title 17 zoning setbacks, and confirming it is built to the current International Residential and Building Codes.
Even an exempt shed still needs plumbing and mechanical permits if those systems are installed, the exemption never applies inside a floodway, and it does not excuse compliance with the fire code or any other Mason County, state, or federal regulation that otherwise applies to the structure.
Violations & Fines
Building a shed over five hundred seventy-six square feet, taller than ten feet, or closer than ten feet to another structure without first obtaining a building permit is a misdemeanor under Mason County Code Section 1.04.010, punishable by up to a five-hundred-dollar fine, ninety days in jail, or both. The building official may also require an after-the-fact permit at triple the standard fee under Section 1.10.030.
Frequently Asked Questions
What size shed can I build without a permit in Mason County?
Do I need paperwork to build an exempt shed in Mason County?
Does an exempt shed in Mason County still need plumbing permits?
Sources & Official References
Other rules in Mason County
How Mason County compares: Shed Permit Requirements by City·Compare Mason County to another location·View the Washington accessory structures overview
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