Civil Engineering for Sunken Driveway Projects
Serving public and private clients in Illinois, Indiana, Wisconsin, Michigan, and Iowa.
The sunken driveway is a popular home renovation in the City of Chicago. Adding a lower-level garage is an easy way to add significant value to a city dwelling. Chicago's stormwater ordinance requires special calculations for homeowners planning to construct a sunken driveway on their property to minimize the risk that floodwater from the street will come down the driveway and flood the basement. This change was added to the storm code because the City has had numerous events where the street flooded over the top of the sidewalk, and the overflow for the entire block was into the basement of an unsuspecting homeowner.
The ordinance is there to protect everyone and now requires that an engineer prepare a plan to determine the overflow path of the stormwater in the gutter in the event that the catch basin nearest the property is blocked. The analysis determines whether the sewer will overflow down the street to another block or will the new driveway become the overflow point? This requires a topographic survey of the gutter along the subject block and then down to the next cross street until an overflow point is found. Calculations are required for the amount of runoff expected in the gutter and the depth of the gutter flow. This is then compared to the grade at the back of the sidewalk to ensure the driveway can be constructed safely. Builders should not automatically assume that a sunken driveway will work in every location, but contracting with an experienced engineering firm like Bono Consulting can bring clarity and a definitive answer to whether or not a sunken driveway can be constructed at your home.