A property owner needs a "Certificate of Zoning Compliance," which authorizes a basement conversion. It certifies the number of dwellings permitted on the property and the legality of a remodeled basement. For example, say the basement of a "two-flat" building that has two above-ground apartments is converted to a third apartment. Its certificate indicates that the property is zoned for two units only, which means the basement isn't approved for use as a residence. The basement was, therefore, completed without city permission -- it's illegal.
Spotting Illegal Basement Apartments
Dampening Illegal Building Plans
A Chicago basement apartment can extend to any depth below the floor grade as long as the space has sufficient protection from leakage. Floors and walls must be impervious to water penetration from both surface and underground water. Basement apartments must have a minimum ceiling height of 7 and a half feet.
Planning an Exit
A basement apartment must have its own entry and exit. The exit must be accessible without passing through a bedroom, bathroom or toilet. Basements of less than 800 square feet in a multi-unit dwelling need only one exit. Exits must prevent rodent entry, rain and surface water drainage entry, and all exterior doors and windows must fit well and have no cracks.
Beating the Cold
Basement apartments must have adequate heating and hot water. Living, dining and sleeping areas must receive natural light, therefore, a basement apartment needs at least one window. The apartment may use either natural or mechanical ventilation. Each room must have a minimum glazed window area of no less than 8 percent of the room's floor area.
Many of the rules that apply to regular residences also apply to basement apartments. For example, the city sets standards for electrical and plumbing systems to prevent fires and flooding. Basements apartments must also be fitted with smoke detectors and they require carbon monoxide detectors if the heating system burns fossil fuel.