TL;DR (generated, confidence: high)

Portland requires building permits for accessory structures over 200 sq ft or taller than 15 feet, with exceptions for small non-habitable structures, large lots, and different rules for habitable spaces.

Key points:

Accessory structure is a stand-alone building smaller and dependent on the main structure, including garages, carports, sheds, greenhouses, pool pumphouses, covered patios, and decks. (Garages, sheds, and accessory structures ↗)
Building permit required for accessory structures over 200 sq ft (interior wall measurement) or taller than 15 feet (grade plane to roof height). (Garages, sheds, and accessory structures ↗)
Non-habitable structures 200 sq ft or smaller need zoning permit only, not building permit. (Garages, sheds, and accessory structures ↗)
For lots over 2 acres: no building permit if structure under 400 sq ft AND minimum 20 feet from property lines and other structures. (Garages, sheds, and accessory structures ↗)
Habitable structures (bedrooms, living rooms, kitchens, studies, etc.) require building permit regardless of size. (Garages, sheds, and accessory structures ↗)

Entities: definition: Accessory structure · Habitable structure | permit_type: Building permit · Zoning permit | threshold: 200 square feet · 15 feet · 400 square feet

Garages, sheds, and accessory structures

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Source: Garages, sheds, and accessory structures ↗ Last modified: Sun, 19 Apr 2026 20:05:52 GMT

Definitions

Accessory structure. A stand-alone building that is smaller and dependent upon the main structure on the lot.
- Examples of accessory structures:
  - Garages, carports, sheds, greenhouses, swimming pool pumphouses, covered patios, and covered decks.
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Erosion control. The practices and techniques used to prevent or minimize soil movement or loss.
Impervious area. The area of a property that does not allow rainwater to drain naturally into the ground. This can include buildings, structures, and paved areas.
Living or habitable space. A space in a building for living, sleeping, eating, or cooking.
- Examples of habitable space:
  - Bedrooms, living rooms, studies, recreation rooms, kitchens, dining rooms, and other similar spaces.
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Lot or site slope. The measure of how flat or steep the land is. Shown as a percentage.

Do you need a permit?

You will need a building permit to build, tear down ↗, or change an accessory structure* that is:

Over 200 square feet (measured from the interior of exterior walls)
- Non-habitable structures 200 square feet or smaller.
  - A building permit is not needed, but you may need a zoning permit ↗.
and/or taller than 15 feet (measured from the grade plane to the average height of the highest roof surface)

For lots over 2 acres, you do NOT need a building permit if:

The structure is under 400 square feet, AND
The structure is located a minimum of 20 feet from property lines and other structures.

*For non-heated and non-habitable accessory structures. A building permit is required for habitable structures ↗ regardless of size.