Is Your Built-Up Roof Hail-Proof?

Hail Damage to Built Up Roofing: Critical 2025 Guide

Why Built-Up Roofs Face Unique Hail Damage Risks

Hail damage to built up roofing can be subtle and severe, making it challenging to assess. While these commercial roofing systems are generally resistant to hail, understanding their vulnerabilities is crucial.

Key Facts About Hail Damage to Built-Up Roofing:

Gravel-surfaced BUR systems resist hail up to 2 inches in diameter with no membrane damage.
Smooth-surfaced BUR systems are more susceptible to damage from smaller hailstones.
Damage often occurs below the surface, making visual detection difficult.
Unprotected areas like blisters and flashings are most vulnerable to impact.
Professional assessment is essential since damage may not be immediately visible.

Built-up roofs are common on commercial properties. These multi-layered systems use asphalt-coated reinforcements and bitumen for waterproofing. When hail strikes, the asphalt can crack or displace, and the underlying felt may fracture, allowing water infiltration that leads to premature deterioration.

Hail causes approximately $1 billion in annual property damage across the U.S. With millions of properties affected by damaging hail events annually, understanding your roof’s vulnerability is vital.

I’m Denton Belnap, founder of High Country Exteriors. I’ve seen how hail damage to built up roofing can compromise commercial buildings across Idaho. My experience shows that early detection and proper assessment are key to preventing costly long-term damage.

Understanding How Hail Affects BUR Systems

When hailstones strike a built-up roof, understanding the impact helps you protect your investment and spot problems early.

Hail damage to built up roofing begins on contact. The impact creates a chain reaction through the BUR system’s layers, with energy spreading outward and downward. On gravel-surfaced systems, the stones act as shock absorbers, dispersing impact force. This gravel protection is the first defense. On a smooth-surfaced BUR, the energy directly hits the asphalt flood coat.

Trouble begins when the impact cracks or displaces the asphalt. A compromised protective layer makes the underlying felt vulnerable. Membrane punctures and felt layer displacement create pathways for water intrusion. The most serious damage is often hidden below the surface. The felt reinforcement can fracture even if the surface looks normal. This hidden damage leads to water infiltration, damaged insulation, and structural issues.

For a deeper dive into how commercial roofing systems work together to protect your building, check out our guide on Commercial Roofing Systems.

Gravel-Surfaced vs. Smooth-Surfaced Roofs

Not all built-up roofs handle hail the same way; the surface type makes a huge difference.

Gravel-surfaced BUR systems offer the best hail resistance. The gravel absorbs and scatters impact energy, often shattering the hailstone. Testing shows gravel-covered roofs can withstand hailstones up to 2 inches in diameter without membrane damage. The gravel may be displaced, creating craters, but the membrane remains intact.

Smooth-surfaced BUR systems are more vulnerable. Without gravel, hail delivers its full force to the asphalt flood coat. This direct impact resistance challenge means even moderate hail can cause asphalt displacement and cracking. On newer smooth roofs, damage may appear as concentric fractures. Older, brittle roofs might suffer felt fracture and spalling. This susceptibility difference is why many prefer gravel-surfaced roofs in hail-prone areas.

The Role of Substrate and Support

The substrate beneath your BUR is as important as its surface. Softer substrates like insulation boards or plywood don’t provide the same solid backing as a concrete deck. When hail hits a membrane over soft insulation, it can flex and deform more easily. This flexibility increases the risk of membrane damage, as deeper indentations can stress the asphalt and felt layers to their breaking point.

Unsupported areas like membrane blisters, loose flashings, and ridged sections are prime targets for hail, as they are already weak points. Flashings are particularly vulnerable as they often lack solid support, and even moderate hail can damage these areas, creating entry points for water.

The insulation type also influences damage. Rigid insulation provides better support than softer materials. A concrete deck generally offers superior impact resistance compared to a plywood deck. Age is also a factor; older roofs with brittle asphalt have increased vulnerability to smaller hailstones. Regular maintenance is crucial for extending hail resistance.

Identifying Hail Damage on Your Built-Up Roof

Identifying hail damage to built up roofing can be tricky. The gravel on many BUR systems can hide underlying damage. A roof might look fine from the ground but have significant membrane damage upon closer inspection. A quick glance isn’t enough; a proper, safe, on-roof inspection is necessary, as serious damage is often subsurface. Professional assessment is crucial because scattered divots can signal widespread membrane compromise.

Hail damage patterns are distinctive, but without experience, it’s easy to miss them or confuse them with normal aging. Our experience in Idaho’s hail-prone regions is a key advantage for our clients.

Primary Signs of Hail Damage to Built-Up Roofing

When inspecting a BUR after a hailstorm, we look for specific signs that the weather protection is compromised. These indicators often mean a dramatically shortened roof lifespan.

Divots or craters in the gravel are the most obvious signs on gravel-surfaced roofs. Hail creates depressions that expose the black bitumen, which stands out against the weathered surface.
Spalling or fracturing of the asphalt flood coat is clearer on smooth surfaces. On new roofs, this may appear as concentric fractures. Older, brittle roofs may show more dramatic spalling, with chunks breaking away.
Star-shaped fractures are concerning as they indicate ruptured reinforcement plies. These deep cracks, often found during detailed inspections, spread from the impact point.
Doughnut-shaped patterns can be created by large hailstones on ballasted roofs, where gravel is pushed aside in a ring around the impact zone.
Membrane bruising is a dangerous, nearly invisible sign. The surface may look fine but feel soft or spongy when pressed. This indicates broken or separated underlying plies, creating a weak spot that will fail.

Finding these signs clustered or following a storm’s path indicates functional damage needing immediate attention.

Differentiating Hail Damage from Common Roof Issues

Differentiating hail damage to built up roofing from normal wear and tear is tricky. Property owners often mistake gradual aging issues for storm damage.

$Image showing a side-by-side comparison of alligatoring cracks and hail-induced fractures - hail damage to built up roofing$

Alligatoring is a common issue mistaken for hail damage. These fine, interconnected cracks are caused by UV exposure and aging, not impact. They are shallow and lack the distinct impact points of hail.
Membrane blisters, caused by trapped moisture or air, can be mistaken for impact damage. However, hail can rupture a blister, which will then show characteristic star fractures.
Asphalt bubbles are smaller blisters, usually from installation. They are not hail damage but are vulnerable to hail strikes.
Interply voids are bonding failures from construction or aging, not storm damage. However, these weak spots will show typical hail damage patterns if struck.
Weathering and mechanical damage can create isolated damage. The key difference is that hail damage shows consistent patterns, often on slopes facing the storm. Hail-caused fractures also have sharper, fresher edges than older damage.

Factors That Influence Hail Damage Severity

When evaluating hail damage to built up roofing, severity depends on a combination of factors. The wrong mix can turn a moderate hailstorm into a roof replacement nightmare.

Hailstone size is a key factor. A hailstone’s impact energy increases exponentially with its size; a 3-inch hailstone has over 100 times the impact energy of a 1-inch stone. This is why larger hail is so destructive. Size isn’t everything; hailstone velocity, wind speed, and impact angle also matter. Wind-driven hail strikes at an angle, creating more stress on the roof membrane.

Roof age and condition are critical. As BURs age, the asphalt becomes brittle. A new, flexible roof can withstand hail that would shatter an older system. A poorly maintained roof with existing issues is more vulnerable. Research supports this, as detailed in this study: P9.3 HAIL DAMAGE TO BUILT-UP ROOFING.

How Hail Resistance is Tested and Rated

The roofing industry uses rigorous impact testing to measure hail resistance. This involves launching ice ball tests at roof samples at controlled velocities to simulate a hailstorm. These tests show that gravel-covered BURs can withstand 2.0-inch ice balls without membrane damage, while smooth-surfaced samples are much more vulnerable.

Standardized ratings help in selecting materials for hail-prone areas. UL 2218 Class 4 is a key impact resistance rating. For commercial roofs, FM 4470 and FM 4473 standards are even more stringent, evaluating the entire roof assembly. Systems with FM Global Class 1-H, 1H, or 1SH ratings are designed for severe hail. These ratings are crucial for projects in hail-prone areas. Explore the standards in the FM 4473 Rated Systems documentation.

An effective strategy is using high-density cover boards between the insulation and membrane. These boards act like armor, spreading impact energy over a wider area, which makes a huge difference in performance.

Your Post-Hailstorm Action Plan

After a hailstorm, the thought of hail damage to built up roofing can be stressful. A solid action plan makes all the difference. Our team has helped many property owners in Idaho and Montana manage this situation. The key is to act quickly and safely, document everything, and get professional help to prevent small problems from escalating.

Safety always comes first. Never climb onto a wet or damaged roof. Stay safe while gathering information for repairs and insurance claims.

Immediate Steps After a Storm

Once the storm passes, several critical steps can affect your insurance claim and repair process.

Note the exact date and time of the storm. Insurance companies require this information.
Conduct a visual inspection from the ground. From a safe spot, look for displaced gravel, dark spots, or visible cracks. Also, check for collateral damage to siding or cars, as this supports your claim.
Photograph everything. Take wide and close-up shots of any damage. These images are crucial evidence for your insurance claim.
Check inside for leaks immediately. Look for water stains or wet spots. Use buckets to minimize interior damage if you find active leaks.

Even if you see no damage, don’t assume you’re in the clear. Hail damage to built up roofing is often hidden. For immediate help, see our Roof Repair Services.

The Importance of Professional Inspection and Maintenance

With hail damage on built-up roofs, what you can’t see often matters most. A professional inspection is essential. Our certified inspectors perform a hidden damage assessment, looking for membrane bruising, subsurface fractures, and other subtle signs. We use specialized equipment for subsurface damage detection and moisture detection to find trapped water before it causes major structural problems.

We also provide insurance claim assistance. We know what adjusters look for and provide the detailed documentation to strengthen your claim. Addressing hail damage quickly prevents further issues. Our comprehensive Roof Maintenance Programs help keep your roof resilient.

Long-Term Consequences of Unrepaired Hail Damage to Built-Up Roofing

Delaying repairs for hail damage to built up roofing is a costly mistake.

Accelerated aging occurs when unrepaired damage exposes underlying layers to the elements. A 20-year roof can fail in just a few years.
Water infiltration is a silent killer. Tiny cracks allow water to seep in and spread, worsening with freeze-thaw cycles.
Insulation damage follows water intrusion. Wet insulation is ineffective, raising energy bills, and can lead to mold growth.
Structural deterioration is the scariest consequence. Persistent water intrusion can rot roof decks and supports, potentially leading to collapse.

This all leads to a reduced roof lifespan, forcing a premature and expensive roof replacement. Prompt repair is the smart financial choice. If damage is extensive, we’re here to help with professional Roof Replacement Services when needed.

Frequently Asked Questions about Hail Damage to Built-Up Roofing

After a decade of working with property owners in Idaho and Montana, I’ve found that the same questions about hail damage to built up roofing arise after a storm. Here are some straight answers.

How large does hail need to be to damage a built-up roof?

This answer isn’t simple. Generally, hailstones over 3/4 inch in diameter are the minimum size considered to cause property damage. However, built-up roof systems are quite tough.

Gravel-surfaced BUR systems can resist hailstones up to 2 inches in diameter in lab tests. The gravel acts like armor, dispersing impact energy. However, unprotected or older, brittle roofs are more susceptible to smaller hail. Flashings, blisters, or smooth-surfaced sections can be damaged by 1-inch hailstones. Age is a major factor, as asphalt becomes more brittle over time.

Can I file an insurance claim for cosmetic hail damage?

Insurance coverage varies significantly by policy. Some policies cover cosmetic damage that doesn’t affect function, while others only cover “functional damage” that reduces weather resistance or lifespan.

The key is to have a professional assess if the damage is functional. This assessment strengthens your claim. We document fractures or felt damage, proving it’s functional damage that will lead to premature failure, not just cosmetic marks. What appears cosmetic on a BUR often indicates deeper issues. Adjusters understand this when it’s properly documented.

How long do I have to file a claim after a hailstorm?

Time is critical. Most policies have a filing deadline, often six months to two years from the date of loss. Do not wait that long.

Acting quickly with a professional inspection and documentation is critical for claim acceptance. Delaying can lead to further deterioration, which an insurer might attribute to neglect. Waiting can lead to denied claims as fresh hail damage becomes complicated by weathering. Schedule an inspection within days of a hail event. We document everything, differentiating fresh hail damage from pre-existing conditions. This creates a clear timeline that insurers trust.

Even without immediate leaks, hail can compromise your roof’s integrity. Damage may not appear until the next storm or winter’s freeze-thaw cycles. Acting early protects your building and your claim.

Protect Your Investment with a Professional Assessment

With hail damage to built up roofing, what you can’t see can hurt you. A small, seemingly harmless crack or bruise can become a major problem. Waiting for professional help often turns a minor repair into a major headache.

Built-up roofs are tough but not invincible. Hail damage is often subsurface and hard to spot. Membrane bruising, fractured plies, and compromised flood coats can weaken your roof without obvious signs. Early detection by a professional is essential to protect your investment.

At High Country Exteriors, we’ve spent over 10 years helping property owners in Idaho and Montana assess their roofs after severe weather. Our expert inspections use tools like infrared cameras and moisture meters to find hidden moisture and damage that others miss.

Catching hail damage early can save you tens of thousands of dollars. A prompt repair prevents the accelerated aging, water infiltration, and structural deterioration that can lead to a premature roof replacement. We’ve seen roofs fail years early due to unaddressed hail damage.

Our teams are ready to serve you across Idaho, including Rigby, Twin Falls, Rexburg, Driggs, Idaho Falls, Shelley, Blackfoot, and Pocatello, as well as in Montana, including Helena, Belgrade, Billings, Bozeman, Dillon, and Butte. We understand the unique weather challenges in these areas and know how to spot the specific patterns of damage that our regional hailstorms create.

Don’t gamble with your building’s protection. A professional assessment provides peace of mind by clarifying your roof’s condition and the steps needed to maintain it.