Illinois has seen its share of severe weather, but some hailstorms stand out not just for the damage they caused — but for the sheer size of the hailstones themselves.
In 2015, parts of Illinois experienced hailstones measuring over 6 inches in diameter, ranking among the largest hail ever recorded in the state. While events like this grab attention, they also create a dangerous misconception: that only massive hail causes roof damage.
In reality, hail doesn’t need to break records to compromise a commercial roofing system.
Here’s what Illinois’ largest hail events teach us — and why building owners should focus on impact behavior, not just size.
A Brief Look at Illinois’ Largest Hail Events
Illinois regularly ranks among the top states for hail frequency. Some of the most notable events include:
June 2015 – Coal City, IL: Hailstones measured over 6 inches in diameter, causing widespread structural and roof damage
April 2023 – Central Illinois: Large hail combined with high winds damaged commercial buildings across multiple counties
Recurring summer storm systems: Producing golf ball– to baseball-size hail that impacts thousands of roofs each year
While these extreme events are rare, moderate-to-large hailstorms are not — and they’re often just as problematic for commercial roofs.
Why Hail Size Alone Doesn’t Tell the Full Story
When it comes to roof damage, size is only one factor. In many cases, smaller hail causes more long-term issues than record-breaking stones.
Here’s why.
1. Impact Density Matters More Than Diameter
A storm producing thousands of 1–2 inch hailstones can be more damaging than a few isolated softball-size impacts.
High-density hail events can:
Create widespread membrane bruising
Damage seams across large roof sections
Crush insulation evenly over the roof surface
This type of damage often looks uniform and subtle — making it easy to overlook without a close inspection.
2. Wind Speed Changes How Hail Hits the Roof
Hail rarely falls straight down. In Illinois storms, hail is often driven by strong lateral winds, increasing impact force at angles roofing systems aren’t designed to absorb.
This can lead to:
Torn or weakened flashing
Damage at parapet walls and roof edges
Compromised attachment points
Even smaller hailstones can strike with enough force to fracture membranes when wind speeds are high.
3. Roof Type and Age Play a Major Role
Two buildings can experience the same hailstorm and have completely different outcomes.
Damage severity depends on:
Roof system type (TPO, PVC, EPDM, modified bitumen)
Roof age and prior repairs
Existing wear, ponding, or thermal stress
Older roofs or systems already under stress are far more vulnerable — even during “non-severe” hail events.
4. The Most Serious Damage Often Isn’t Visible
One of the biggest challenges with hail damage on commercial roofs is that leaks don’t always appear right away.
Hail can:
Create micro-fractures in membranes
Compress insulation without tearing the surface
Weaken seams that fail months later
By the time water intrusion becomes noticeable, damage may already be widespread beneath the surface.
Why Post-Hail Inspections Matter — Even After Smaller Storms
Because hail damage isn’t always obvious, post-storm inspections are critical after any hail event — not just record-setting storms.
A professional inspection can identify:
Impact bruising and membrane fractures
Insulation compression
Early warning signs of future failure
Early documentation also helps protect building owners if insurance claims become necessary down the road.
The Bottom Line: It’s Not Just About Big Hail — It’s About Smart Evaluation
Illinois’ largest hailstones make headlines, but it’s the more frequent, less dramatic storms that quietly shorten roof lifespans and lead to costly repairs.
Understanding how hail behaves — and how commercial roofing systems respond — is key to protecting your building long-term.
Jewett Roofing works with property owners across Illinois and Missouri to assess hail damage accurately, document findings clearly, and recommend practical next steps — before small impacts turn into major problems.
