Guide to Roof Hail Impact Resistance

Introduction

Hail impact resistance refers to a roofing material’s or roof system’s ability to withstand damage from hailstones. In hail-prone regions, roofs are the first line of defense against ice balls that can range from pea-sized to baseball-sized. Large hail can reach terminal velocities of 50–100+ mph, carrying enough kinetic energy to dent metal, crack tiles, shatter shingles, or puncture membranes.

Damage modes include surface dents, coating/granule loss, substrate compression, cracks, or outright punctures. Impact-resistant roofing is designed and tested to resist such damage, reducing the likelihood of leaks or costly failures during hailstorms.

This guide explains how hail-resistance is defined and rated, who certifies it, how lab tests simulate hail, and what those ratings mean in practice. I cover both steep-slope roofs (asphalt shingles, wood, tile, metal, slate, synthetic) and low-slope roofs (single-ply membranes, built-up roofing, modified bitumen, spray foam, etc.), noting typical performance and key factors like substrate and installation. I’ll also provide some real product examples with official ratings, and end with practical tips.

My goal here is to help homeowners and property managers make informed roofing decisions to mitigate hail damage, understand the limits of hail resistance claims, and help you make sure your new roof meets insurance or code requirements for hail-prone areas.

Impact Rating Is Not a Warranty

Impact-resistance ratings are performance test results, not promises of future performance. A UL 2218 Class 4 or FM 4473 Class 4 label only means the product passed a specific laboratory impact test on the day it was tested. It does not guarantee that your roof will remain undamaged in every storm, or that the manufacturer will cover any hail damage at all under warranty.

Most roofing product warranties, especially for asphalt shingles, explicitly exclude hail, wind-blown debris, and other impact damage as “acts of nature.” The impact rating is intended to help consumers and insurers compare materials objectively, not to create a contractual obligation for the manufacturer.

Some commercial low-slope roof assemblies may carry limited hail coverage under the manufacturer’s warranty. For example, certain single-ply or modified-bitumen systems tested to FM 4470 Severe Hail or Very Severe Hail and installed exactly as tested, including specified cover board, insulation type, and attachment method, can be covered. These cases are clearly spelled out in the assembly’s published warranty terms and usually specify a maximum hailstone size (often 2 inches or less).

For any roof system, homeowners and property managers should verify hail coverage directly in the warranty document or with the manufacturer’s technical department. Unless hail resistance is specifically warranted by hail size and test standard, assume that the rating is informational only and that hail impact remains the owner’s risk.

Although impact ratings are not warranties, they can have financial value through insurance discounts. Many insurance companies offer insurance premium reductions in hail-prone regions, typically between 5 and 30 percent, for verified Class 4 impact-resistant roofs. These programs are based on actuarial data showing lower claims frequency, not on any manufacturer guarantee.

To receive a discount, homeowners typically must provide documentation proving that the installed product is Class 4. So impact ratings can save you money through insurance incentives, but they do not obligate the manufacturer to pay for hail damage.

Hail Impact Testing and Rating Systems

Multiple standards exist to evaluate hail impact resistance. These tests use different methods – steel balls or ice balls – to simulate hail strikes in a controlled way. Materials or assemblies that pass are assigned ratings (Classes 1–4 or descriptive levels like moderate/severe hail). It’s important to understand what each test involves and how to interpret the ratings in real-world terms.

UL 2218 “Steel Ball” Impact Test

Underwriters Laboratories (UL) Standard UL 2218 is a widely used test for impact resistance of prepared roof covering materials (primarily steep-slope products like shingles, tiles, metal panels). UL 2218 is often called the “steel ball test.”

In this test, a series of solid steel balls of increasing diameter are dropped from specified heights onto the roof sample, which is mounted on a standard substrate. The impact energy simulates hailstones of equivalent size striking a roof.

There are four class ratings: Class 1, 2, 3, 4, with Class 4 being the highest (most impact resistant).

• Class 1 uses a 1.25-inch (31.8 mm) steel ball
• Class 2 uses a 1.50-inch (38.1 mm) steel ball
• Class 3 uses a 1.75-inch (44.5 mm) steel ball
• Class 4 uses a 2.00-inch (50.8 mm) steel ball

Each ball is dropped twice onto the same spot from the height required to produce the kinetic energy of hail of that size in free-fall (for example, a 2-inch ball is dropped from 20 feet).

The pass/fail criterion is strict: no cracking, tearing, splitting or rupture is allowed through to the underside of the sample. After each impact, the panel is turned over and examined – if any “evidence of opening” (visible cracks or punctures) is seen on the back side, the material fails. Superficial damage on the top surface (dents, scuffs, or granule loss) is not counted as failure.

To achieve a UL 2218 Class 4 rating, the product must survive two drops of a 2-inch steel ball from 20 ft with no underside cracks. (A 2-inch steel ball weighs roughly 1.2 lbs.) Lower class ratings correspond to a material successfully resisting smaller maximum hail impacts: Class 3 withstands a 1.75″ ball from 17 ft, Class 2 resists a 1.5″ ball from 15 ft. UL 2218 was developed in the mid-1990s after catastrophic hailstorms, to allow manufacturers to rate and market “impact-resistant” roofs.

Today, Class 4 is often the advertised rating for hail-resistant shingles and other coverings. It’s important to note that UL 2218 focuses on functional damage, not cosmetic issues. A Class 4 roof might still get surface dings or granule loss from hail, but as long as it doesn’t split or crack all the way through, it passes. In the real world, insurers may still pay to replace roofs for extensive cosmetic damage or granule loss on Class 4 shingles, even though the shingle “passed” the UL test by not splitting.

So UL 2218 is a useful comparative standard – a Class 4 product is tougher than Class 3, etc. – but it does not guarantee a hail-proof roof in all conditions. It means the product can resist cracking against hail up to about 2″ in diameter in a controlled test. Hail larger than the test limit, or high-angle wind-driven hail, or multiple repetitive impacts, can still damage any roof. Also, UL 2218 does not age or weather the samples – new products are tested, which may not account for long-term aging or weathering effects on impact resistance.

FM 4473 “Ice Ball” Impact Test

Factory Mutual’s FM 4473 is another standard for impact resistance, primarily used for rigid roofing materials (including shingles, tiles, panels) and recognized by FM Approvals (often for commercial products). Instead of steel balls, FM 4473 uses actual ice balls launched at the test sample.

The ice spheres are standardized, made by freezing water in molds under controlled conditions to specific diameters – nominally 1.25, 1.5, 1.75, and 2.0 inches, corresponding to Classes 1 through 4. Using ice rather than steel is intended to more realistically simulate hailstone behavior (ice can shatter or flatten on impact, distributing energy differently than a solid steel ball).

In FM 4473 testing, the ice ball is propelled by an air cannon at a target speed that yields the desired impact energy for that size hail. For example, a 2″ (51 mm) diameter ice ball of about 0.135 lb mass is shot at about 117 ft/s (80 mph), representing a severe hailstrike with about 29.5 ft-lb of kinetic energy. The pass/fail criteria are similar to UL – the material must show no visible cracking, breakage or perforation after impact.

Products are rated Class 1 through 4 based on the largest ice-ball impact they withstand without failure. A Class 4 rating in FM 4473 equates to surviving 2″ ice impacts (the highest level). In practice, UL 2218 and FM 4473 class ratings are often considered equivalent benchmarks: Class 4 in either test is typically required for the highest hail-resistant roofing products.

Many asphalt shingles, metal panels, and tiles are marketed as “Class 4 impact rated” referencing one or both standards. The key difference is the projectile: FM 4473’s ice ball can simulate the shattering and energy dispersion of real hail more closely than a steel ball. Ice balls have lower density than steel and will fracture on a hard impact, which may impart a slightly more distributed impact load.

Steel balls, being unyielding, deliver a concentrated impact force at a single point and can in some cases exaggerate damage on brittle materials like tile or slate. Because of this, a material tested to UL 2218 should also do well under FM 4473, but there are instances where a product could pass one and not the other.

Building codes: Some insurance-backed programs or local codes accept either UL 2218 or FM 4473 certification for roof coverings. The International Building Code (IBC) has at times referenced impact standards for hail-prone regions (though historically with some confusion in earlier editions).

As of 2021, IBC Section 1504.7 recognizes UL 2218 or FM 4473 Class 2 (or higher) for impact resistance in low-slope roof coverings in hail zones. Many insurance companies, notably in Texas and the Midwest, offer premium discounts for roofs that are UL 2218 Class 3 or 4 rated. (Texas, for instance, maintains a list of criteria for products that can qualify for impact-resistant roofing credits under UL 2218.) These discounts can range from 5% to over 30% and typically require documentation of the new roof’s rating.

Always check with local code and insurer requirements – Class 4 is the gold standard, but Class 3 products may meet minimum code in some areas. Insurers will likely require the highest rating for maximum discounts.

FM 4470 Roof Assembly Ratings

UL 2218 and FM 4473 test individual roofing materials. FM 4470, on the other hand, is an extensive approval standard that tests entire roof assemblies (for commercial low-slope roofs) for a range of properties – fire, wind uplift, foot traffic, durability, and hail.

FM 4470 classifies roof assemblies by hail resistance using descriptive ratings: Moderate Hail (MH), Severe Hail (SH), or the newest Very Severe Hail (VSH). These correspond to the different size hailstones the assembly can endure. Historically, FM defined Moderate as hail ≤1.5″ and Severe as 1.75″ (golf ball size). Around 2016, responding to reports of larger hail sizes, FM introduced Very Severe Hail for >2″ hail (billiard-ball size and above).

The FM 4470 hail test method uses steel balls for MH and SH, and ice balls for VSH, with aging of roof assembly samples to test long-term performance. Specifically, to earn an FM Class 1-SH (Severe Hail) rating, a roof assembly must withstand a 2″ steel ball dropped from a height of 141.5 inches (11.8 ft) onto both new and artificially weathered samples, delivering about 14 ft-lb of energy (18.98 joules). Moderate Hail (MH) uses the same 2″ steel ball but dropped from 81 inches (6.75 ft), for about 8 ft-lb of energy.

For the Class 1-VSH (Very Severe Hail) rating, the test propels a 2-inch diameter ice ball at 152–160 ft/s (about 105 mph) at the roof assembly; three variants are tested: one new, one UV-weathered, and one UV + heat aged for 42 days. These ice impacts (at about 53–58 ft-lb) are far more destructive, simulating extreme hail conditions.

After these tests, the assembly is inspected for cracks, fractures, or membrane splits; any failure disqualifies the assembly for that rating. Assemblies that pass are listed in FM’s RoofNav database as Class 1-MH, 1-SH, or 1-VSH. FM ratings apply to the entire roof system, not just the membrane. An FM Approved assembly for severe hail will specify the exact membrane, attachment method, insulation type/thickness, and any cover board or ballast used. For instance, a single-ply membrane roof system might achieve Severe or VSH rating only if a 1/2″ cementitious cover board is installed above the insulation.

FM’s testing and historical data have shown that the firmness of the substrate under a roof membrane is critical: a hard cover board greatly improves impact resistance, while a soft compressible insulation alone allows hail to dent in and cause membrane stress tears. (This is illustrated in FM literature: large hail on a soft-backed membrane creates a “dimple” that can split the roof, whereas the same impact on a roof with a high-density cover board leaves little damage.)

Many commercial building insurers (including FM Global) require FM-rated assemblies for facilities in hail-prone regions. FM Global’s loss prevention maps (Data Sheet 1-34) delineate areas of Moderate, Severe, and Very Severe hail exposure across the U.S.

If your building is in a “Severe” zone, FM would recommend a Class 1-SH roof; in the core “VSH” hail belt (like parts of TX/OK/CO and northern Plains), a Class 1-VSH assembly is recommended for best protection. It’s worth noting that since the VSH classification’s introduction, thousands of new assemblies have been tested; as of 2025, over 33,000 FM-rated roof assemblies are listed as VSH, and about 4,400 of those even achieved it without a cover board (for example, some thick built-up roof or ballasted systems).

Cover boards are still typically the key to meeting higher hail ratings for most single-ply systems.

UL 2218 Class 4 and FM 4473 Class 4 are the typical ratings of an impact-resistant product, while FM 4470 SH/VSH is the mark of an impact-resistant system. Homeowners with steep roofs will usually look for the UL 2218 rating on shingles, etc., whereas commercial building owners with flat roofs should look for FM-approved assemblies (or an equivalent performance test) that match their hail exposure.

In either case, knowing the rating and its limitations helps set expectations: for example, a Class 4 shingle roof should resist functional damage in most hailstorms, and a VSH commercial roof should survive even extreme hail events (up to about 2.5-inch diameter).

Other Test Methods and Research

Aside from the above industry standards, there are a few other test methods and research programs worth mentioning:

ASTM Standards:

ASTM International has published some methods related to impact on roofing, such as ASTM D3746 (an old standard for impact resistance of bituminous roofing, using a weighted plunger) and ASTM D4272 (impact resistance of rigid roofing by impact bar). However, these never gained the broad adoption that UL and FM tests have.

In some building codes around 2000, ASTM D3746 was referenced for roof impact, but it was later dropped in favor of the UL/FM standards. There is (or was) ongoing ASTM work to develop a new “very severe hail” test, likely building on FM 4473’s ice ball method for wider use. Generally, when manufacturers advertise impact ratings today, they refer to UL 2218 or FM tests, not ASTM, except for some specialty cases.

Miami-Dade TAS 114 Appendix F:

In Florida’s High Velocity Hurricane Zone, there is a test (TAS 114-11 Appendix F) involving impact of steel balls on roof assemblies adhered to insulation. This is primarily to assess hail damage potential for roofs in South Florida, and it’s somewhat analogous to an assembly test for hail (it even references FM’s procedure).

IBHS Hail Research:

The Insurance Institute for Business & Home Safety (IBHS) has conducted extensive hail studies to better replicate natural hail effects. IBHS developed a laboratory method to grow artificial hailstones with precise density and hardness, and built a hail cannon to fire them at full roof sections. In 2019 IBHS introduced an impact testing program for asphalt shingles that differed from UL 2218 by using ice spheres and measuring granule loss and substrate bruising, not just cracks.

This research revealed that not all UL 2218 Class 4 shingles perform equally well in the field – some Class 4 shingles still suffered significant surface damage from realistic hail that wouldn’t count as “failure” in UL’s criteria. As a result, IBHS proposed a new impact rating that accounts for that, though as of 2025 the industry still primarily uses the UL classification on products.

The key takeaway is that Class 4 is necessary but not always sufficient – the construction (material formulation, reinforcement) matters. IBHS also found that aged shingles can become more brittle and less impact-resistant, so a brand-new Class 4 shingle may lose resilience after years of UV and heat exposure. This underscores why some standards (like FM’s VSH) deliberately test aged samples as well.

Historical NBS/NIST Studies:

Even back in 1960s, the National Bureau of Standards (NBS, now NIST) studied hail effects on roofs. A 1969 NBS series fired ice balls at built-up roofs, shingles, slate, clay tile, etc., documenting damage thresholds. They confirmed what is still true: metal and gravel-surfaced BUR were the most hail-resistant roofs at the time, surviving hail up to 2.5″ with no damage, while materials like slate, asbestos-cement, and standard asphalt shingles were damaged by much smaller hail. That study helped establish early guidelines that firm substrates and robust surface materials matter, and those findings remain consistent with modern tests.

Conclusion:

Multiple testing protocols exist, but UL 2218 Class 4 is the common benchmark for impact-resistant shingles and tiles, while FM’s severe hail ratings are critical for commercial flat roofs. When evaluating roofing options, look for these ratings in official listings or data sheets, and beware of marketing claims without documentation.

Also remember that these tests simulate hail strikes under laboratory conditions; extremely rare events (softball-sized hail, wind-driven side impacts, etc.) can exceed these standards. No roof is “hail proof,” but using impact-rated materials and assemblies significantly improves the odds of avoiding functional damage in most hailstorms.

Hail Performance by Roofing Material and System

Hail impact resistance varies widely by roofing material. Factors include the material’s hardness or flexibility, thickness, the support beneath it, and how it’s installed. This section summarizes the typical hail resistance expectations for common roof materials and systems. Steep-slope materials are usually rated as individual products per UL 2218 or FM 4473; low-slope systems are often rated as assemblies per FM 4470. Key variables that can improve or worsen hail performance are noted for each.

Steep-Slope (Pitched) Roofing Materials

(Covers pitched roofs on homes or buildings; generally shingles, tiles, metal panels, etc.)

Asphalt Shingles (Composition Shingles):

Asphalt shingles are the most common residential roofing material in the North America. Standard asphalt shingles typically have no specific hail rating and can be damaged by relatively small hail. Hail can bruise the shingle (knock off mineral granules and dent the asphalt substrate) or in severe cases puncture it.

Many manufacturers offer impact-resistant shingles that achieve Class 3 or Class 4 ratings. These Class 4 asphalt shingles usually incorporate modifications like a rubberized asphalt (SBS polymer-modified asphalt) or a reinforcing mesh on the back of the shingle to prevent cracking. SBS-modified shingles are more flexible and can absorb hail strikes without fracturing.

Other designs use a polymer composite backing that holds the shingle together on impact. These shingles commonly carry a UL 2218 Class 4 label and are advertised for hail regions. They also resist wind damage better than unmodified shingles.

In practice, Class 4 shingles greatly reduce fractures. One study found Class 4 asphalt shingles had a median hail damage threshold around 2-inch hail, versus 1.25-inch for standard shingles. They will still get cosmetic damage in big hailstorms (dents and granule loss), but are less likely to leak. Aging plays a role: a brand-new Class 4 shingle roof might survive golf-ball-size hail, but after 15–20 years of UV exposure the asphalt typically becomes more brittle, lowering its hail resilience.

Impact-rated shingles are a cost-effective upgrade in hail country. They install and look the same as regular shingles, with a modest initial cost increase, and can yield insurance discounts (often 5–30% off premiums) in many states. When buying, verify the shingle’s rating on the actual packaging and the product data sheet; also verify that the hip and ridge cap shingles being used are similarly impact-rated (some insurers require the accessory ridge caps to be Class 4 as well).

Important: Hail impact ratings such as UL 2218 Class 4 show how a shingle performed in a controlled laboratory test, not how it will behave in every real storm. These ratings are not warranties and are not included in the manufacturer’s shingle warranty coverage. They simply indicate that the product met a certain test standard at the time of testing.

Manufacturers do not guarantee that a Class 4 shingle will remain undamaged in all hail events or that insurance will cover cosmetic or functional damage. Always read the actual warranty document to understand what is and is not covered.

Examples of Class 4 impact resistant asphalt shingles include:

• Owens Corning TruDefinition® Duration FLEX® (SBS modified)
• CertainTeed NorthGate® ClimateFlex®
• Malarkey Legacy® Scotchgard™
• GAF Timberline^® ArmorShield II
• Atlas StormMaster® Shake
• IKO Nordic^™

Wood Shingles & Shakes:

Natural cedar shingles and shakes have a mixed performance with hail. Cedar roofing materials are often simply unrated/untested. New, thick cedar shakes can resist smaller hail without splitting, and some do meet Class 3 or even Class 4 impact ratings when tested under UL 2218. At least one manufacturer advertises its western red cedar shingles as UL 2218 Class 4 compliant.

Cedar’s natural fibrous structure can absorb impact to a degree. However, as wood roofs age and dry out, they become more brittle. A 10+ year old cedar shake is quite likely to crack under moderate hail. Statistically, wood roofs suffer heavy damage in large hailstorms (hail ≥1.5″ will split many shakes). Hail can also cause impact dents in the wood that may not leak initially but can reduce the roof’s lifespan.

Thicker shakes do better than thin shingles. Unless specifically impact-rated and relatively new, wood roofing is considered one of the more hail-vulnerable roofing materials. Many insurance companies have surcharges for wood roofs in hail-prone states.

If you have a wood shake roof in a hail zone, you should inspect it after every significant hail event; even if it’s not leaking, cracked shakes should be replaced to keep the roof sound. For new installations in areas with high hail risk, consider treated cedar shakes that come with an impact rating, or even synthetic or metal shakes as an alternative for better durability.

Clay Tiles (Terra Cotta Tile):

Clay roofing tiles are hard but thay can be brittle. Hail can crack clay tiles. Under UL 2218, many clay tiles achieve only Class 1 or 2 (if tested at all), meaning even 1″ hail might cause some breakage. Thicker, heavier tiles generally perform better.

Some manufacturers have tested clay tiles to higher levels. Roof tile manufacturer Verea claims that at least some of their Spanish clay tiles were certified to FM 4473 Class 3 (surviving 1.75″ ice balls at ~70 mph). This implies that strong, well-supported clay tiles can resist golf-ball hail. Usually, tiles that are thicker or have fiber reinforcement (or those laid over a solid deck with foam attachment) perform better.

Still, larger hail (≥2.5″) will devastate most clay tile roofs – tiles can shatter on impact. The good news is that tile roofs are typically installed with special underlayment that provides a secondary water barrier; even if some tiles break, the felt or membrane underneath should prevent interior leaks until repairs are made. Also, hail damage to clay tile tends to be localized (individual broken tiles can be replaced) rather than a total loss of the roof.

When selecting clay tile for hail regions, choose products that have an established impact rating or have passed the FM/UL tests, and consider installation methods that improve impact resistance. Be aware that after a major hailstorm, finding replacement tiles of the same style/color can be tricky, especially if the product was custom-made or imported.

Concrete Tiles:

Concrete roofing tiles (which can mimic the appearance of clay or slate) are generally more impact-resistant than clay due to their material properties – concrete tile is a bit less brittle and commonly made thicker and heavier. Many concrete tiles achieve Class 3 or Class 4 ratings in UL 2218.

Flat profile concrete tiles by some brands have a UL 2218 Class 4 listing. Concrete S-tile has been shown to be able to achieve FM 4473 Class 4, withstanding 2-inch ice ball impacts at 80 mph without cracks. These tests indicate a well-made concrete tile can handle hail up to 2 inches in diameter.

In real storms, concrete tiles have proven durable against moderate hail; often only a few tiles might crack under 1.5 – 2-inch hail, whereas clay would have many more breaks. However, very large hail (≥3″) can still break concrete tiles. Like clay, concrete tile roofs rely on underlayment for additional watertightness, so even if some tiles fracture, catastrophic leaks can often be avoided.

One issue with concrete roof tile is edge vulnerability which stems from their thinner, more fragile interlocking corners/edges. Hailstones hitting these parts of a tile can break or chip it, whereas impacts on the main part of the tile wouldn’t do that. Some newer concrete tile systems use foam adhesive or full boarding under tiles, which improves their hail resistance by supporting the tile. Textured or thicker tiles may mask or resist cosmetic chips better than flat, thin tiles.

Homeowners and property managers in hail regions with concrete tile should still inspect their roof after a hailstorm. Cracked tiles should be replaced to keep the roof system sound (and to maintain any warranty). Overall, concrete tile is a durable material in moderate hail climates, but not invulnerable in extreme hail events.

Metal Roofing (Panels and Shingles):

Metal roofs are often promoted for their hail resistance. In terms of functional impact resistance, metal is highly resilient: aluminum, steel, copper, and zinc roofing will not crack or puncture from hailstones that would destroy rigid materials. Virtually all metal roof systems can attain UL 2218 Class 4 (the highest rating).

Stone-coated steel shingles and standing seam steel panels will normally be Class 4 rated. In tests, even giant hail (3–4″) typically will not puncture a metal panel, especially if it’s over solid decking. However, metal is prone to cosmetic damage: a hailstone can leave dents in the metal surface. Softer metals like aluminum, copper, and zinc will dent more easily than steel. Even thick steel may show dimples from large hail, though stone-coated steel (with a textured granular coating) tends to hide or prevent minor dents.

It’s noteworthy that UL 2218 ignores cosmetic denting, so a metal roof can be full of dents but still be a “Class 4” roof (no cracks or holes). After a severe hailstorm, metal roofs will often remain waterproof but not look so good any more. Some insurance policies exclude cosmetic hail damage for metal roofs (but offer a premium reduction in exchange), meaning they won’t pay for appearance-only dents. Homeowners should be aware of this and decide if minor denting is acceptable.

From a performance standpoint, metal roofs are great at resisting hail impacts. They are tough and won’t fail unless the hail is extreme to the point of puncturing the metal or deforming seams (which is very rare). Through-fastened metal panels (exposed-fastener roofs) could potentially have their fastener washers damaged by very large hail, but again, this is uncommon.

If you choose metal in a hail-prone region, steel (especially Galvalume steel in 24 ga (0.024″) or thicker) is recommended for best dent resistance. Aluminum and copper roofs may need to be heavier gauge to avoid dents. Standing seam panels with foam insulation backing or solid decking under them will resist impact better than those spanning open purlins.

Overall, a Class 4 metal roof offers superb hail protection. You can expect it to remain structurally intact through almost any hailstorm. You may have some dings and dents to live with (although stone-coated steel or heavily textured panels can hide the impacts).

Slate (Natural Stone):

Traditional slate roofing (natural quarried stone shingles) has high strength in some respects (long-lasting, fireproof) but can be fractured by hail or careless foot traffic. Roofing slate is a brittle material that’s typically only 1/4-inch thick in standard installations (standard slate thickness). Hail around 1 – 1.5 inches in diameter can crack or chip standard slates, especially if they hit near the unsupported middle of a piece. In the 1990s NBS tests, even relatively small hail (1-inch) caused some damage to standard slate shingles, and larger hail easily cracked them.

Thicker slates (3/8″–1/2″) or harder varieties (like Vermont slate) do better. The National Slate Association reports that 3/8-inch slate can achieve a Class 4 rating. But large hail (2″+) will likely break or chip many slates on a roof. Since slate quality varies from quarry to quarry, it’s important to verify the impact resistance rating of any slate material with the slate producer.

When slate cracks, the pieces usually remain in place, so immediate leaks are uncommon unless the hail was extreme. But those slates will need replacement to restore full roof integrity. In places like Colorado or Oklahoma, many historic slate roofs have been lost to hail damage over time. Some insurers charge high premiums for real slate in severe hail areas due to the expensive repairs when it does get hit.

If you love slate and live in a hail zone, consider softball-sized hail as an existential threat. It could destroy the roof. An alternative is installing a polymer composite synthetic slate (see the next section) which offers a similar look with far better impact resilience. If you have an existing slate roof, keep up with inspections – hairline cracks from smaller hail can be hard to see but may grow with freeze-thaw cycles. Replacing individual slates will help preserve the rest of the roof.

Synthetic Composite Shingles/Tiles:

This category includes polymer-based or rubber-based roofing tiles that imitate wood shakes, slate, or tiles. Examples are polymer slates/shakes manufactured by DaVinci Roofscapes or Brava Roof Tiles, rubber/polyurethane shakes made by CeDUR, and other composite roofing sheets. These products are almost always engineered to achieve UL 2218 Class 4 ratings. In fact, one of their main selling points is superior impact resistance.

As an example, DaVinci’s polypropylene-based synthetic slates and shakes all have Class 4 impact ratings and have survived dozens of hailstorms with no damage in field reports. These materials tend to have some flexibility, so hailstones bounce or break while the impact force is harmlessly absorbed rather than cracking the material. They also don’t use granules, so there’s no granule loss issue.

A Class 4 synthetic composite roof can typically withstand golf-ball to tennis-ball size hail (1.75–2.5″) without functional damage, although there may be occasional surface scuffing. A synthetic shake might get a slight indent from a huge hail strike but not break.

Unlike with other steep slope roofing materials, it’s common for synthetic composite roofs to be warrantied against hail up to a certain size (some offer warranty coverage for any hail up to 2″ or so). These products are generally more expensive upfront than asphalt shingles or even metal, but if you live in a very hail-prone area (“Hail Alley”), they can provide peace of mind and potentially lower insurance costs.

Just ensure the specific product is listed as Class 4 (most are) and installed per manufacturer specs (sometimes the Class 4 rating may depend on a specific underlayment or installation method).

One thing to watch: some early-generation synthetic slates (from the 1990s) had issues becoming brittle after years of UV exposure, which could reduce impact resistance. Newer formulas seem to have solved this with UV stabilizers. As always, check for any independent certification or code evaluation.

Synthetic composite shingles/tiles/slates are among the best choices for resisting hail.

Table 1: Hail Impact Resistance – Residential Roofing

Scroll table sideways on smaller screens.

Low-Slope (“Flat”) Roofing Systems

(Typically commercial roofing, but also “flat” residential roof areas.)

Built-Up Roofing (BUR):

Built-up roofs consist of multiple plies of reinforcing felts and layers of bitumen (asphalt or coal tar pitch), often finished with a thicker top layer of bitumen with gravel embedded in it (a “gravel-surfaced BUR”). Decades of experience and testing show that gravel-surfaced BUR is one of the most hail-resistant systems available. The layer of gravel provides excellent impact resistance: hailstones impact the gravel, which dissipates the energy by shifting or breaking the stones instead of damaging the roof membrane below.

A oft-cited study found no damage to BUR with pea gravel surfacing even from 2.5″ ice balls, unless the substrate was extremely soft. In the field, gravel BUR roofs in hail zones often come through unscathed, while single-ply roofs in the same area are punctured. BUR with aggregate surfacing generally qualifies for the highest FM hail ratings. Many are FM Severe or Very Severe Hail approved essentially by default.

Smooth-surfaced BUR (no gravel, typically surfaced with an emulsion and an aluminum coating for UV resistance) is less resistant. Large hail can gouge or crack the asphalt membrane. Still, because BUR has multiple layers, hail damage doesn’t necessarily leak; it usually takes a serious crack through several plies to open a hole. Historically, the “threshold of damage” for smooth BUR was around 1.5–1.75″ hail.

To improve that, some smooth-surfaced BURs will include a mineral-surfaced cap sheet (basically a hybrid system with a modified bitumen cap sheet) to absorb impact. Overall, BUR’s redundancy and mass make it excellent against hail.

If you have a BUR roof, maintaining the surfacing (ensuring even gravel coverage or intact cap sheet) is key. After a hail event, look for displaced gravel exposing asphalt or any cracks in the bitumen. BUR typically only needs minor repairs after hail (if any). It’s a solid choice for low-slope roofs in hail-prone areas, although it’s getting harder to find a roofing contractor who installs BUR these days.

Modified Bitumen (Mod-Bit):

Modified bitumen roofs are made using rolls of reinforcement fabric saturated and coated with polymer-modified asphalt, usually applied in two layers, a base sheet and a cap sheet. They come in two main types: SBS-modified (styrene-butadiene-styrene), which is more flexible and does better in cold weather, and APP-modified (atactic polypropylene) which is a bit stiffer and does better in hot weather. Mod-bit roofs can be installed with torched or mopped seams, and the top layer (cap sheet) typically has mineral granules like an asphalt shingle.

A properly installed 2-ply mod-bit system offers very good hail resistance. Mod bit systems are known for their resistance to mechanical damage from foot traffic or impacts. Many modified bitumen products are UL 2218 Class 4 (some cap sheets just by themselves qualify as Class 4 when adhered to a plywood deck in tests). SBS-modified sheets in particular can absorb impacts without fracturing because the asphalt is rubbery. APP sheets are more rigid and can crack under sharp impact, but in a multi-ply system they’re still resilient.

Mod-bit roof assemblies regularly earn FM Severe Hail ratings, especially if they are installed over a cover board. For example, a two-ply SBS system over a 1/2-inch gypsum roof board can typically meet FM SH or Class 4. Even without an underlying hard cover board, a mod-bit roof membrane over a firm insulation like high-density polyiso can often qualify as moderate-to-severe hail resistant. Remember that only full roof assemblies with all components specifically identified will be rated.

In my experience in North Texas (where there’s a lot of hail) mod-bit roofs generally perform very well in heavy hail when it comes to not actually leaking. Instead of punctures that compromise the roof, they typically get some surface granule loss or slight fractures in the top layer that don’t propagate through the base layer. Hail the size of golf balls (1.75-inch) will typically not cause actual leaks in a mod-bit roof. Hail around 2.5-inch might bruise or crack the cap sheet, but usually not shatter it, so leak emergencies are uncommon.

Owners should inspect the roof’s surface after a hailstorm: look for areas of excessive granule loss or any visible cracks. Fractures in the cap sheet should be patched and areas with lost granules should be coated or have granules reapplied.

Mod-bit is a top choice for hail durability, and many mod-bit products and systems are Class 4 rated.

Single-Ply Membranes (EPDM, TPO, PVC):

Single-ply roofs are lightweight and cost-effective, but they can be vulnerable to hail if the system is not properly designed. These membranes (whether EPDM rubber, TPO, or PVC membranes) are typically installed over roof insulation. The membrane itself can be anywhere from 45 mil (1.1 mm) thick to 90+ mils (2.3 mm).

The problem with hail comes when a hard hailstone impacts a thin membrane that’s resting on a soft, compressible insulation (like standard polyisocyanurate foam). The insulation gives way, creating a localized depression, and the membrane is momentarily stretched into that depression and when hit from above. This tension can cause the membrane to split or puncture.

Many real-world hail failures on EPDM/TPO involve fractures that look like starbursts or cracks in the membrane, often above insulation board joints or above fastener plates where stress is concentrated. Early single-ply roofs in hail zones had a poor track record. 1.5-inch hail could sometimes puncture a 45 mil membrane and cause leaks.

System design solutions have greatly improved single-ply hail resistance: The primary one is using a hard cover board between the membrane and insulation. Boards like 1/4-inch or 1/2″ fiberglass-faced gypsum (like Georgia Pacific’s DensDeck or USG’s Securock), or 1/2-inch high-density polyiso, or even 3/4-inch plywood, provide a firm, unyielding surface so the hail impact force is spread out.

Membranes over cover boards have dramatically higher impact tolerance. In FM tests, a TPO or PVC roof that fails moderate hail on bare insulation might pass Very Severe Hail with a cover board. In fact, nearly all FM Class 1-VSH roofs employ a cover board, unless the insulation itself is very high density.

Another approach is using thicker or reinforced membranes. A 90 mil thick EPDM or a fleece-backed TPO has more cushion and strength to resist cracking. Thermoset EPDM (rubber) membranes tend to perform better than thermoplastics (TPO and PVC) because EPDM is very elastic. It can stretch on impact and rebound without tearing. Tests by the EPDM Roofing Association showed even aged EPDM of decent thickness withstood 3″ simulated hail in many cases.

PVC membranes, on the other hand, can become brittle with age (from plasticizer loss) and the earliest PVC roof membranes were notorious for cracking during hailstorms or even if you just walked on them in very cold weather. Modern PVC formulations and the addition of reinforcing scrim to PVC roof membranes pretty much solved this issue, and PVC can achieve VSH ratings too. But historically PVC had hail issues (many insurers at one point excluded hail on older PVC roofs). Hail can still be an issue for very old PVC roofs that have outlived their design life.

TPO roof membranes are somewhere in between. It’s a thermoplastic like PVC but it doesn’t need plasticizers to stay flexible, so it doesn’t get as brittle as drastically. Still, it’s not as rubbery as EPDM, and it does become more vulnerable the older it gets.

For any type of single-ply membrane, fleece-back versions (where the membrane is laminated to a fleece backing) provide extra padding and are typically adhered with a foam adhesive that itself helps diffuse hail impact force. These systems have shown excellent hail resistance, often achieving FM Severe Hail without a separate board (the fleece acts like one).

Single-ply roof systems can be designed to meet the highest hail standards: a fully-adhered TPO system can be an FM VSH assembly, as can a PVC system, or an EPDM system. Many manufacturers list specific “hail-rated assemblies,” so refer to those if you have a flat roof in hail country.

Plan for hail by using thicker membranes, cover boards (or high-density insulation top layers), and by choosing systems tested for hail. If you inherit a single-ply roof without those, you might consider adding a coating or overlay for protection (though the benefits may be limited).

Always inspect single-ply roofs after hail. Even a small puncture can turn into a massive leak on low-slope roofs. If you find one puncture, consider that others may exist, so a thorough, professional inspection might be needed. Consider keeping emergency roof repair tape on hand so you can make temporary repairs until you can get a roofer out to your roof (which can take a while after a major storm).

All in all, single-plies can be satisfactorily hail-resistant when designed right, but they have a wide performance range depending on the system configuration.

Spray Polyurethane Foam (SPF) Roofing:

SPF roofs are created by spraying polyurethane foam insulation directly on the roof deck or over a prepared existing roof, then coating it with a protective coating (acrylic, silicone, or urethane). These roofs have a solid, seamless surface and the foam (typically 2 – 6-inches thick) provides insulation. SPF cushions hail impacts to some degree. The foam has some give.

Small hail (≤1-inch) will typically just ding the surface. However, large hail can cause craters in the foam. The impact can compress the foam and puncture or crack the brittle coating layer. The result looks like pockmarks; if the coating is breached, UV rays can degrade the foam in those spots relatively quickly.

An SPF roof’s hail performance largely depends on the coating type and thickness. A heavy polyurethane coating with an embedded layer of aggregate (one common SPF topcoat) provides a fairly hard protective layer and can achieve an FM Severe Hail rating. A thinner acrylic coating is more easily punctured. In FM tests (4470), some SPF systems are rated Moderate Hail and a few with special coatings are Severe Hail.

In practice, hail at around 1.5 – 2-inches might put divots in an SPF roof but usually won’t go through all the way to the deck, meaning immediate leaks will be rare unless the hail is extreme. A benefit of this roof system is that SPF is easily repairable. If you get hail damage, a contractor can patch the divots with new foam and recoat the damaged areas relatively simply, restoring the surface.

SPF roofs have generally good hail resistance but require timely maintenance of the coating. Owners should recoat the foam every 10 – 15 years as specified by the manufacturer, because an eroded coating will make the foam vulnerable to UV degradation and water freeze damage. SPF can handle moderate hail, especially with high-quality coating, but baseball-sized hail will damage it, requiring repairs. The foam itself adds resilience by absorbing and dispersing impact force, so catastrophic hail penetration is uncommon.

For hail-prone areas, ask your SPF installer about hail-rated systems (some have Miami-Dade or FM approvals for impact).

Liquid-Applied Membranes and Roof Coatings:

Some roofs are essentially a liquid-applied, fabric-reinforced membrane (e.g. a cold fluid-applied modified polyurethane, or a reinforced acrylic system). Other have roof coatings applied over existing roofs for various reasons. The hail resistance of these materials can vary widely. A fully reinforced liquid-applied membrane (with the fabric embedded in layers of the coating) can perform very well, sometimes achieving a Class 4 rating in lab tests.

In contrast, an unreinforced coating typically depends on the substrate (the existing roof it was applied to) for its hail resistance. It may crack under smaller hail because the substrate below might be weakened. Simple coatings are not roof systems/roof assemblies and will not be rated as such. You don’t normally count on a roof coating for impact resistance.

Generally, thicker is better. A carefully-applied 60-mil liquid membrane with fabric will take more abuse than a 20-mil sprayed on coating. If a liquid-applied system is FM Approved for Severe Hail, it will be in their listings (some do exist). Certain PMMA-based liquid systems over concrete were tested to FM Severe Hail, but details are manufacturer-specific.

Coatings on metal roofs can help prevent paint chipping from hail, but won’t stop dents. Coatings on single-ply membranes can mask minor defects but a big hailstone can still puncture the underlying aged membrane. The main thing to note: if you are relying on a coating-only roof (like a silicone restoration on a mod-bit or an acrylic on an old metal roof), understand that its hail protection is limited by the substrate. It might delay leaks but not fully prevent damage if the substrate is weak.

Always check manufacturer data – some roof coating systems have undergone UL 2218 tests. Inspect liquid-applied roofing/roof coatings after a hailstorm for any splits or cracks. Small repairs and touch-ups (re-coating damaged locations) can extend the effectiveness of the coating after moderate hail.

Table 2: Hail Impact Resistance – Commercial Roofing

Low-Slope / Flat Roof Systems: (Usually rated as complete assemblies; hail performance depends on membrane + substrate together.)

Scroll table sideways on smaller screens.

Practical Advice

Choosing a hail-resistant roof is about reducing risk: No roof is completely hail-proof, but the right materials and design can often prevent significant damage. Here’s a practical checklist for homeowners and property managers:

Know Your Hail Risk: Find out your region’s hail exposure (insurance maps or FM’s hail zone maps). If you’re in a moderate hail area, a Class 3 product might be acceptable; in hail hotspots (Great Plains, Front Range, etc.), try to use materials with the highest ratings (Class 4 or FM SH/VSH).

Look for Impact Ratings: When replacing your roof, ask for products that are UL 2218 Class 4 or FM 4473 Class 4. For low-slope roofs, ask about FM hail approvals (MH, SH, VSH). Don’t accept vague claims; request documentation. The actual material packaging and the spec sheet should state the UL 2218 class or FM classification. If a contractor is unsure, have them find out or choose a different product.

Use Complete Systems: Ensure the entire roof assembly is designed for hail, not just the outer layer. For single-ply roofs, that means including a cover board or high-density insulation layer. Many membrane warranties require a cover board in hail zones for full coverage, and for good reason, as it can be the difference between no damage and a lot of damage. Likewise, if you’re installing Class 4 shingles, use the matching Class 4 ridge caps and hip shingles and other hail-resistant roof accessories.

Confirm Installation Methods: How a product is installed affects hail performance. For example, metal panels over open framing are more prone to damage than when they’re fully supported by a deck. Make sure your contractor follows the manufacturer’s recommended installation for the impact rating. The shingle nailing pattern, or the mod-bit lap adhesion…all of this stuff matters.

Deviations might reduce the system’s impact resistance and/or void any hail provisions in the warranty. Check that any foam adhesive or fasteners used won’t create issues (large hail can sometimes puncture a membrane at a poorly installed fastener). Use of proper accessories (like starter strips, ridge pieces) all play a role.

Expect Cosmetic Damage: Understand that “impact-resistant” means resistant to functional failure (leaking), not that the roof will look pristine after hail. Dents in gutters, slight dings in a metal roof, or granule loss on shingles can happen even if the roof is Class 4.

Many Class 4 shingles purposely sacrifice some surface granules upon impact, as this dissipates energy but doesn’t compromise the shingle’s waterproofing integrity. So don’t panic if you see some visible effects after a storm; the roof may still do its main job just fine. Cosmetic damage can be fixed for aesthetics (e.g. touch-up paint for metal, replacing a few shingles), but often it’s not urgent.

Maintain and Inspect: Hail-resistant roofs usually require less repair, but not zero. After a significant hail event, always inspect your roof (or have a professional inspect it). Look at roof penetrations, skylights, vents, ridge caps, and in roof valleys where hail may hit at angles.

Even Class 4 shingles can have localized damage (like a torn shingle if hail and wind was working together). Flat roofs should be checked for punctures or loss of surfacing. Regular maintenance (keeping drains clear, replacing age-deteriorated building sealants) also helps the roof perform under hail by ensuring water has a path to drain if some minor damage occurs.

Don’t Forget Other Components: A hail-resistant roof covering is key, but also consider skylights, AC units, and other rooftop equipment. A skylight that isn’t hail-rated (e.g. standard plastic dome) can shatter under the same hail that your Class 4 shingles survived. Consider hail-rated skylights or install hail screens. HVAC units can be protected with hail guards (metal louvered shields or mesh) to prevent fin damage. These measures complement your hail-resistant roof so that one weak component doesn’t cause interior damage while the roof itself held up.

Insurance and Documentation: If you invest in an impact-resistant roof, tell your insurance company. Many insurers require a certificate or proof (e.g. the UL 2218 classification label or contractor’s invoice stating the Class 4 product) to apply a premium discount. Also find out whether your policy covers cosmetic damage or not – you may want a policy that covers cosmetic damage, especially if you have metal roofing. Keep records of the product specs and install date; in case of a future claim, you want to show that you used rated materials (some insurers inspect roofs after a claim to see if it really was IR rated).

Plan for the Worst: Even with the best roof, a freak hailstorm could overwhelm it. Have an emergency plan: know a reliable roofer who can do quick storm repairs (many roofers get swamped after hailstorms). For commercial buildings, have tarps or temporary patch materials like repair tape or roof cement on hand. Consider impact-resistant window films or shutters for windows too: giant hail can break windows long before the roof fails. And make sure your property insurance is up to date for hail.

By following these tips – choosing proven materials, installing them correctly, and maintaining them properly – you can dramatically improve your roof’s chances of survival during a hailstorm. In high-risk hail areas, investing in a Class 4 or severe-hail-rated roof is often cost-effective over time, when considering insurance benefits and the damage and repair costs you avoid.