With limited buildable area in the City of Chicago, sometimes a driveway will be designed to slope down below grade from the sidewalk in order to meet all the needs of the construction project. While it’s not always ideal, sometimes it’s the only option to maximize the site's potential. These sloped driveways are allowed in Chicago, but a special “sunken driveway” permit is required.
The City of Chicago defines a sunken driveway as any driveway that slopes down below grade from either a street or an alley. This permit will help determine the necessary steps to protect the proposed building from flooding conditions.
In the early 2000s, the City implemented a "Rain Blocker" system to reduce basement flooding. The system has reduced the amount of water that can enter the city's sewer system and allows for more water to be stored in the gutter line of the street. However, this additional water in the gutter line has cause an unfortunate problem where the stormwater could pond too high, overtop the sidewalk, and flow down the sunken driveway and into the garage.
Bono Consulting has worked with numerous projects with sunken driveways and we're familiar with the required calculations. For example, the survey area of the site needs to be expanded much more than what is typically required for a standard building permit. Often, the entire street front and a block or two will need to be surveyed to determine the tributary area where water might flow. Our team uses that information to calculate the ponding height and ensure the sidewalk is a higher elevation and will protect the property from potential water damage.
Additionally, the City requires a driveway profile to be prepared that shows that the driveway is not too steep, is safe to drive down, and that vehicles will not bottom out when driving on it.
Bono Consulting has extensive experience with the City of Chicago in obtaining sunken driveway permits and can assist residential property owners and developers in obtaining these permits.