The Illinois egress window code requires at least one emergency escape opening in every sleeping room and every basement of a home, sized to a net clear opening of 5.7 square feet, at least 24 inches tall and 20 inches wide, with the sill no more than 44 inches off the floor. Since Public Act 103-0510 took effect in January 2025, these International Residential Code requirements apply statewide, including in jurisdictions that previously had no local building code.1Illinois Capital Development Board. Building Codes and Regulations Local codes still govern where they exist, but they cannot fall below that baseline.
Minimum Size and Dimensions
Every egress window has to provide a net clear opening of at least 5.7 square feet. That is the actual space available when the window is fully open, not the size of the glass or the frame. The opening also has to measure at least 24 inches tall and at least 20 inches wide. Hitting 5.7 square feet with the wrong combination of height and width still fails: both minimums have to be met independently.
Windows at or above grade level get a small break, needing only 5.0 square feet of net clear opening. Below-grade windows, which most basement egress windows are, stay at 5.7. This distinction catches homeowners who measure a walkout basement window, clear 5.0 square feet, and assume they’re fine.
The bottom of the opening cannot sit more than 44 inches above the finished floor. The window has to be operable from inside without keys, tools, or special knowledge, which rules out painted-shut sashes and any lock that needs an allen wrench. Fall prevention devices and window opening control devices that comply with ASTM F2090 are allowed, provided they release under normal operation.
Where an Egress Window Is Required
The IRC calls for an emergency escape and rescue opening in three places: every sleeping room, every basement, and every habitable attic. A basement used as one open living area needs at least one. Once you frame walls and create bedrooms in that basement, each bedroom needs its own opening in addition to any basement-level one.
The window has to open directly into a public way, or into a yard or court that is at least 36 inches wide and leads to a public way. A window that opens into an enclosed patio, or into a space blocked by a fence with no exit, does not count.
Two narrow exceptions exist:
- A basement used exclusively to house mechanical equipment, totaling no more than 200 square feet, does not need an egress window.
- In a home with an automatic sprinkler system installed to IRC Section P2904, basement sleeping rooms do not need their own egress windows if the basement has either one egress opening plus a code-compliant exit, or two separate code-compliant exits.
The sprinkler exception is mostly useful in new construction where the builder designs around it. Retrofitting a sprinkler system into an existing house purely to skip an egress window rarely pencils out.
Window Well Rules
When the window sits below grade, a window well is required. The well must provide at least 9 square feet of horizontal area, with a minimum width and horizontal projection of 36 inches each. It also has to be large enough for the window to open fully. A well that technically hits 9 square feet but doesn’t give the sash room to swing or slide will fail inspection.
Ladders for Deep Wells
If the well is deeper than 44 inches from its bottom to grade, it needs a permanently attached ladder or steps. Rungs must be at least 12 inches wide on the inside, project at least 3 inches from the wall, and sit no more than 18 inches apart vertically for the full height of the well. The ladder has to be usable with the window in the fully open position, so mounting it directly behind the window’s swing path is a problem. This is the detail most commonly missed in basement egress projects.
Covers
Well covers are allowed and often practical for keeping out rain and snow. Any cover over an egress window well has to be operable from inside the well without tools or special knowledge, and it cannot take more than 30 pounds of force to open. A cover that’s bolted down, or too heavy for a child to push open, violates the code no matter how well it sheds water.
When a Renovation Triggers the Requirement
Existing homes are not required to add egress windows just because the code has been updated. The requirement kicks in when you change the use of a space. The two common triggers: finishing a basement into habitable living space, and converting an existing room into a bedroom. Framing walls and finishing a raw basement into a family room brings in the requirement for at least one egress opening. Adding a bedroom, anywhere in the house, brings in the requirement for one in that room.
Illinois municipalities generally require a building permit for this work. The permit process gets the project reviewed for compliance before construction and inspected afterward. Skipping the permit doesn’t eliminate the requirement. It just means any non-compliance turns up later, usually during a home sale inspection or after an incident, when fixing it costs more.
Where a jurisdiction has its own building code, that local code governs, but as of 2025 it has to be at least as stringent as the IRC. Where no local code exists, the current IRC applies directly.1Illinois Capital Development Board. Building Codes and Regulations Either way, the egress dimensions above are the floor.
What Non-Compliance Costs
Building code enforcement in Illinois happens at the municipal level. Under the Illinois Municipal Code, municipalities can establish code hearing departments to prosecute and correct violations.2Illinois General Assembly. Illinois Code 65 ILCS 5 – Illinois Municipal Code A violation usually starts with a written notice identifying the code provision, the nature of the problem, and the property address, followed by a correction window before penalties escalate.
Fines vary widely by municipality. Some charge a few hundred dollars per violation; others charge substantially more, and each day a violation continues can count as a separate offense.
The bigger exposure is civil. If someone is injured because a sleeping room lacked a code-compliant escape route, the owner faces potential liability under the Illinois Premises Liability Act, which holds owners responsible for maintaining safe conditions on their property.3Illinois General Assembly. Illinois Code 740 ILCS 130 – Premises Liability Act A tenant or guest trapped in a basement bedroom during a fire because there was no egress window is the scenario that produces lawsuits, and the absence of a code-required safety feature makes the plaintiff’s case straightforward.
Insurance and resale add practical costs. Insurers may refuse to cover a loss tied to a known code violation, or raise premiums once they learn about it. Home sales frequently stall when an inspector flags missing or undersized egress windows, because lenders and buyers expect the property to meet applicable codes before closing.
Installation Costs
Professional egress window installation typically runs between $2,300 and $11,000 or more, depending on scope. Below-grade basement installations are the most expensive because they involve excavating around the foundation, cutting through the foundation wall, installing the window and well, and waterproofing the area. A grade-level installation in an above-ground wall costs considerably less, since it skips the excavation and well.
The window unit itself is a small share of the total. Most of the money goes to labor and excavation. Permit fees vary by municipality and are usually modest compared with the installation. Weighed against a stalled sale, municipal fines, or liability after an emergency, the cost is closer to a safety investment than an optional upgrade.