The ordinance permits; it does not compel. A condominium declaration or HOA governing document may still restrict ADUs. That is the explicit guidance Illinois association counsel gave boards ahead of the April 1 effective date, and it is the single most important thing to understand about this change.

Zoning tells you what the City will allow. Your declaration tells you what the association will allow. They are different questions and the stricter one governs.

The 33% rule is where condominium boards get caught

For a building with 5 or more units, conversion units up to 33% of the existing legal unit count is a large number. A 24-unit building could in principle add eight.

But in a condominium, the attic and basement space in question is almost always a common element or a limited common element, not something an individual owner can convert. Creating a new unit from it raises questions the zoning ordinance does not touch:

• does the declaration permit creating new units at all, and on what vote;
• does adding units require reallocating percentages of ownership across every existing unit — which usually requires a supermajority and lender consents;
• who owns the new unit, and what does the association receive for the common element it gave up;
• how are assessments, voting rights and parking recalculated.

None of those are answered by an ADU permit, and a board that says yes to a conversion without answering them has created a title problem.

What a board can do before the first request

Read the declaration now for ADU-relevant language: provisions on subdividing units, on creating new units, on use of common and limited common elements, on leasing, and on amendment thresholds.

Then decide the position in advance and put it in writing. The failure mode is a board making policy under pressure from an owner who has already obtained a City permit and hired an architect.

Where this is heading statewide

The Governor's BUILD package would have legalised ADUs by right in every residential zoning district statewide and preempted home rule — and CAI engaged a sponsor over language that would have allowed middle-housing development in common elements or common areas. It stalled, and the Governor has said he will push it in the veto session.

The Municipal League's REAL counter-proposal goes further in the direction boards care about: it provides that HOAs and condominium associations may not unreasonably prohibit ADUs.

So the carve-out that currently protects Illinois declarations — zoning permits, documents may still restrict — is exactly what both statewide proposals would narrow. A board deciding its ADU position should assume that protection is temporary.

What to watch next

The veto session, and whether any negotiated BUILD/REAL compromise preserves association authority over common elements.