Accessory Structures in Des Plaines, IL

Every city handles accessory structures a little differently. In Des Plaines, Illinois, there are 3 distinct rules that residents and property owners should be aware of. Some are stricter than what neighboring cities enforce, and others are more relaxed. Here is what you need to know.

ADU Rules

Des Plaines has no accessory dwelling unit (ADU) or coach-house ordinance; under Zoning Code Section 12-8-1 a permitted residential accessory structure is limited to a shed, gazebo, pergola, or detached garage and cannot be a separate dwelling, and Illinois has no enacted statute requiring cities to allow ADUs.

Key details: ADU ordinance: None - no ADU/coach-house category. Permitted accessory structures: Shed, gazebo, pergola, detached garage. Non-garage accessory max area: 225 sq ft. Illinois ADU mandate: None enacted (HB3552 pending). Code Section: Des Plaines City Code 12-8-1.

Establishing a second dwelling unit in an accessory structure (shed, garage, or coach house) without zoning approval violates Section 12-8-1 and the use regulations of the underlying residential district. The Community and Economic Development Department can issue a notice of violation, order the unauthorized living space removed or vacated, and pursue citations; legalizing such a unit would require a Variation from the Planning and Zoning Board.

Compared to other cities, Des Plaines takes a harder line on adu rules. The enforcement and penalty structure reflects that.

Shed & Carport Rules

Des Plaines limits a residential shed to 225 square feet and 15 feet tall (never taller than the house), set back at least 5 feet from any property line and off all easements, with a maximum of two accessory structures per lot; a building permit is required and the shed must sit on a 4-inch concrete slab or gravel base under City Code 12-8-1.

Key details: Max area: 225 sq ft. Max height: 15 ft, never taller than the house. Setback: At least 5 ft from all lot lines; off easements. Max accessory structures: 2 per lot (incl. detached garage/carport). Permit fee: $50 (shed).

Building a shed without a permit, over 225 square feet, taller than 15 feet or taller than the house, within 5 feet of a lot line or on an easement, or beyond the two-structure limit violates Section 12-8-1. The Community and Economic Development Department can issue a stop-work order, require the shed to be permitted, relocated, resized, or removed, assess fees and citations, and withhold final inspection approval until it complies; any exception may require a Variation.

Garage Conversions

A Des Plaines detached garage is capped at 720 square feet and 15 feet tall (never taller than the house) with walls 5 feet from property lines, and all sheds plus garages may not cover more than 50% of the required rear yard; converting or attaching a garage to the home requires an Alteration/Remodel (Residential) permit under City Code 12-8-1.

Key details: Detached garage max area: 720 sq ft. Max height: 15 ft, never taller than the house. Wall setback: 5 ft from lot lines (alley: 0 ft in R-1/R-2). Rear-yard coverage: All sheds + garages <= 50% of required rear yard. Attaching/converting: Requires Alteration/Remodel (Residential) permit.

Converting, attaching, or enlarging a garage without the proper Alteration/Remodel or accessory-structure permit, exceeding 720 square feet or 15 feet, violating the 5-foot setback, or exceeding 50% rear-yard coverage violates Section 12-8-1 and the adopted building codes. The City can issue a stop-work order, require permits or removal of unpermitted work, assess fees and citations, and withhold approval until the work complies; any exception may require a Variation.

The Bottom Line

Des Plaines's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Des Plaines is broadly strict or permissive.

Keep in mind that Des Plaines can amend these rules at any council meeting. For the most current version of any rule mentioned here, check the specific ordinance page, where we track updates as they happen.