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Des Plaines, IL Accessory Structures: ADU Rules (2026)

Heavy Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified June 2026

ADU rules in Des Plaines, IL, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

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

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Illinois under recent ADU streamlining laws. The Des Plaines, IL rules below cover local size, height, and setback requirements.

Summary

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.

Accessory uses and structures shall be: 1. Incidental to the principal use or structure served; ... and 3. Subordinate in height, area, bulk, and location to the principal use or structure served.

Source: Des Plaines City CodeView official code

Full Breakdown

Des Plaines does not have an accessory dwelling unit (ADU), coach-house, or 'granny flat' ordinance. The City's official Community and Economic Development handout 'Residential Accessory Structures' and Zoning Ordinance Section 12-8-1 (Accessory Uses and Structures) define a residential accessory structure as a shed, gazebo, pergola, or detached garage or carport - not a separate dwelling unit. Under Section 12-8-1, an accessory structure must be 'incidental to the principal use,' 'subordinate in height, area, bulk, and location to the principal use,' and (other than a detached garage) is capped at 225 square feet and 15 feet in height, which physically rules out a habitable second residence.

The City's permit handouts only list 'Accessory Structure - Shed, Gazebo, Pergola (Residential)' and 'Accessory Structure - Garage (Residential)' as permit types; there is no ADU permit category. Illinois does not currently mandate ADUs statewide: the proposed Local Accessory Dwelling Unit Act (HB3552, 104th General Assembly) was re-referred to the Rules Committee on March 21, 2025 and has not been enacted, so Des Plaines's local restriction controls. A homeowner who wants a livable second unit (for example, finishing a garage or coach house into living space) would need a use Variation or zoning relief from the Planning and Zoning Board.

Violations & Fines

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.

Frequently Asked Questions

Can I build an ADU or coach house in Des Plaines?

Des Plaines has no ADU ordinance. Permitted residential accessory structures are limited to sheds, gazebos, pergolas, and detached garages under Section 12-8-1 - not separate dwelling units. A livable second unit would require a Variation from the Planning and Zoning Board.

Does Illinois require Des Plaines to allow ADUs?

No. As of June 2026 Illinois has no enacted statewide ADU law. A proposed Local Accessory Dwelling Unit Act (HB3552) was re-referred to the Rules Committee in March 2025 and has not become law, so Des Plaines's local rules apply.

Can I live in my detached garage or shed?

No. Section 12-8-1 requires accessory structures to be subordinate and incidental to the home; non-garage accessory structures are capped at 225 square feet, and none may be used as a separate residence without zoning relief.

Sources & Official References

Other rules in Des Plaines

Noise Ordinances: Quiet HoursHeavy Restrictions Noise Ordinances: Construction HoursSome Restrictions Shed & Carport RulesSome Restrictions Garage ConversionsSome Restrictions Noise Ordinances: Vehicle NoiseSome Restrictions Noise Ordinances: Amplified Music & Outdoor SoundHeavy Restrictions Noise Ordinances: Aircraft NoiseFew Restrictions Noise Ordinances: Barking DogsSome Restrictions

All Des Plaines rules

How Des Plaines compares: Easiest Cities to Build an ADU·Compare Des Plaines to another location·View the Illinois accessory structures overview

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