Legal Question in Real Estate Law in Illinois

Assuming by "units" you mean condominium units, NORMALLY the exterior walls are "common elements" that the association would be responsible for. But some condominium declarations are unique to their developments, so the place to start looking would be the definitions and provisions for what constitute "common elements" in your declaration. In "oddball" situations, exterior walls may be "limited common elements" which the declaration MAY impose primary obligations on the actual unit owners, but that is less typical. However, if the leaks are coming from windows, more often the windows may be considered "limited common elements" and again unit owners may have primary responsibility for them. Again, without reviewing the applicable condominium documents, no definitive answer can be given.