Oak Park, IL Fence Regulations: Retaining Walls (2026)

2. Item 4 under 'Building' exempts retaining walls that are not over 4 feet (1219 mm) in height, measured from the bottom of the footing to the top of the wall, unless the wall supports a surcharge or impounds Class I, II, or IIIA liquids, in which case the exemption does not apply regardless of height. 1, Required: the owner or owner's authorized agent must apply to the building official and obtain a permit before it is built. 2, any work performed without the required permit is illegal and constitutes an unlawful act, subject to administrative penalties under the code and any additional Village Code fine.

Because a retaining wall that fails without warning can undermine an adjoining structure or the public right of way, the 4-foot line functions as the Village's threshold for requiring engineered plans and building-official review rather than leaving the design to the property owner alone. A wall proposed in a designated historic district can also require a certificate of advisory review under the same section, independent of its height.