Short Answer
In Chicago an open gazebo or similar single-story detached structure needs no building permit if it is no taller than 15 feet, has no plumbing and has a footprint of 150 square feet or less. Larger structures, attached structures and anything with plumbing need a permit. Chicago's exempt list does not name carports, so confirm with the Department of Buildings. In Seattle the detached-structure exemption stops at 120 square feet of roof area.
Key Takeaways
- Chicago exempts detached open gazebos and similar structures up to 150 sq ft and 15 ft tall without plumbing.
- Seattle's small-structure exemption is 120 sq ft of roof area, single story, detached and outside environmentally critical areas.
- Neither city's exemption list names carports; Seattle's garage guidance covers single-family structures used to park a car.
- Zoning, setback and lot coverage rules apply whether or not a permit is needed.
Quick Facts
| Open gazebo (Chicago) | Exempt up to 150 sq ft footprint, 15 ft tall, single story, detached, no plumbing |
|---|---|
| Roof work on an exempt structure (Chicago) | No permit needed |
| Small detached structure (Seattle) | Exempt up to 120 sq ft of roof, single story, unattached, not in an ECA |
| Larger structure (Seattle) | Usually a subject-to-field-inspection permit; over 750 sq ft needs a full permit |
| Wiring | Lights or outlets need an electrical permit |
From our city pages and each city's open permit data (refreshed October 30, 2026).
Chicago: The 150 Square Foot Rule
Chicago does not require a building permit for installing, altering or removing a single-story detached structure that:
- is not more than 15 feet tall,
- has no plumbing,
- is used as a tool or storage shed, open gazebo, playhouse or similar use, or is purely decorative, and
- has a footprint of 150 square feet or less.
Roof installation, repair or replacement on such a structure also needs no permit. Temporary structures up to 15 feet tall covering no more than 400 square feet are exempt too.
Step-by-Step: What to Do
- Measure the footprint or roof area, including overhangs.
- Note whether it attaches to the house and whether it has plumbing or wiring.
- Compare with your city's exemption limits.
- Check zoning setbacks and lot coverage, which apply even to exempt structures.
- Apply for a permit if any limit is exceeded, plus an electrical permit for wiring.
Seattle: The 120 Square Foot Rule
Seattle's exemption for small detached structures applies when the roof area is 120 square feet or less, the building is single story, sits on a simple slab, pier blocks or soil, is not attached to another building, is not in or near an environmentally critical area, and is used for storage, growing plants or similar unoccupied uses. Other structures usually need a subject-to-field-inspection permit; one over 750 square feet or with beams spanning more than 14 feet needs an addition or alteration permit.
| Limit | Chicago | Seattle |
|---|---|---|
| Exempt size | 150 sq ft footprint | 120 sq ft roof area |
| Height | 15 ft | Single story; zoning caps sheds at 12 ft |
| Attached to house | Not exempt | Not exempt |
| Plumbing | Not exempt | Plumbing permit required |
Carports
Neither city's exemption list names carports. Seattle's garage guidance covers single-family structures used to park a car: most need a subject-to-field-inspection permit if they are 750 square feet or less, single story without a roof deck and with beams spanning 14 feet or less. A carport attached to the house is not exempt in either city, since both exemptions apply only to detached structures. Ask your building department before you build.
Building Departments in the Cities We Cover
Rules in this guide vary by jurisdiction. These are the official departments that issue residential permits in the 15 cities we track, with the city's open-data source for permit records. Each city page shows the rules for roofing, HVAC, solar, fence and deck work.
Before relying on any rule, read the department's current page or call its permit desk. Model-code sections cited here (such as IRC R105) are adopted locally, often with amendments.
Frequently Asked Questions
Do I need a permit for a gazebo?
In Chicago, not if it is an open, detached, single-story gazebo of 150 sq ft or less, no taller than 15 feet and without plumbing.
Do I need a permit for a pergola attached to my house?
Both Chicago's and Seattle's exemptions cover only detached structures, so an attached pergola does not qualify for them.
Does a carport need a permit?
Carports are not on Chicago's or Seattle's exempt lists. Seattle's garage guidance, which covers structures used to park a car, usually calls for a subject-to-field-inspection permit. Confirm with your building department.
Sources
Official sources checked on . Rules change; confirm with the department before you start work.
- City of Chicago: What Types of Work Do Not Require a Building Permit? (Full List) (chicago.gov)
- Seattle SDCI: Sheds (seattle.gov)
- Seattle SDCI: Garages (seattle.gov)