"Class 4" is the label you'll hear most when shopping for a roof in Colorado. It's a real, useful rating, and some towns now require it. It's also widely misunderstood. A Class 4 roof is more likely to survive a hailstorm, but it isn't hail-proof, and the label is not a warranty.
What UL 2218 tests
UL 2218 is the main impact test for roof coverings. A steel ball is dropped twice on the same spot, aimed at the most vulnerable points of a sample. Drop heights range from about 12 to 20 feet. Afterward the sample is bent over a curved form and the back is checked for cracks. A crack is a failure. Dents and granule loss don't count.
| Class | Steel ball diameter | Approximate impact energy |
|---|---|---|
| Class 1 | 1.25 in. | 3.53 ft-lb |
| Class 2 | 1.5 in. | 7.35 ft-lb |
| Class 3 | 1.75 in. | 13.56 ft-lb |
| Class 4 | 2 in. | 23.71 ft-lb |
Notice what that test doesn't measure. A shingle can pass while losing granules, and lost granules shorten its life. Real hail also differs from steel. It comes in irregular shapes, hits at angles and in large numbers, and Colorado has seen stones far bigger than 2 inches.
FM 4473
FM 4473 is a second standard. Instead of dropping steel balls, it fires ice balls from a launcher at set energies, from 1.25 inches (Class 1) to 2 inches (Class 4). A Class 4 ice ball carries about 26.8 ft-lb. To pass, the product must show no visible cracking or breakage. Some products list both ratings.
Not all Class 4 shingles are equal
Impact-resistant shingles get their toughness in different ways. In 2014, the Insurance Institute for Business & Home Safety (IBHS) found that steel-ball tests don't exactly replicate hail. It also found that polymer-modified shingles, made with SBS rubber that keeps the asphalt flexible, outperformed traditional impact-resistant shingles when hit at Class 4 energy.
IBHS now publishes its own ratings using lab-made hailstones. In November 2025, it tested 24 impact-resistant shingle products covering about 95% of impact-resistant shingles sold. Products were rated Excellent, Good, Marginal or Poor. Most rated Good, and none rated Excellent. IBHS doesn't recommend Marginal or Poor products in hail-prone areas, which includes most of the Front Range. Before you pick a product, look up its IBHS rating.
Read the warranty, not the label
A manufacturer can rate a shingle Class 4 and still exclude hail from its warranty. GAF's Timberline AS II is a good example. It's an SBS-modified shingle with a UL 2218 Class 4 rating, a Class A fire rating and top wind ratings. GAF still states that it is not warranted to withstand hail damage.
That's normal, not a trick. It means hail damage on a Class 4 roof is generally an insurance claim, just like on any other roof. When comparing products, ask each contractor for the written warranty and find the hail clause.
Class 4 is a lab rating. It improves your odds; it doesn't guarantee your roof will survive a given storm, and it doesn't create a hail warranty.
Insurance discounts
Some insurers discount premiums for impact-resistant roofs. Colorado law doesn't require it, and amounts vary by insurer. The Colorado Roofing Association says many insurers offer roughly 5% to 25%, but that's an industry claim we couldn't verify. Ask your agent for the actual dollar figure on your policy before deciding.
The 2026 Strengthen Colorado Homes law (SB26-155) doesn't require discounts either. It requires insurers to report annually on resilient-roof discounts and claims, starting no earlier than 2027.
Where Colorado requires Class 4
As of October 2026, these local rules require Class 4 asphalt shingles on replacements. Each has its own trigger and exceptions.
- Fort Collins: when 50% or more of the roof is replaced.
- Unincorporated Larimer County: new construction, replacements and repairs over 25%. A 25% repair triggers replacing the whole roof. Class A fire rating is also required.
- Unincorporated Boulder County: permits submitted on or after March 31, 2025, with a small-repair modification available. This is the county, not the City of Boulder.
- Johnstown: required, with exceptions for matching and repairs.
- Lafayette: reported by the Colorado Municipal League to require impact-resistant new and replacement roofs.
We found no Class 4 requirement in Denver, Aurora, Colorado Springs or Lakewood documents. Confirm with your building department either way.
FORTIFIED and the coming state grants
FORTIFIED is an IBHS program that certifies a whole roof system, not just the shingle. Its Hail Supplement requires shingles rated Good or Excellent in IBHS testing, a stricter bar than Class 4 alone.
SB26-155, signed June 4, 2026, created the Strengthen Colorado Homes Enterprise. Starting in 2027, it's funded by a 0.5% fee on homeowners premiums, and at least 85% goes to homeowner grants for FORTIFIED or equivalent roofs. The earliest grants are expected in 2027. A Division of Insurance official estimated about $7,500 to $10,000 per home. Contractors paid with grant money must be licensed, must not waive deductibles and should repair rather than replace where appropriate.
What it costs extra
The industry estimates a hail-resistant roof adds about $3,000 to $5,000 on a 2,000 square foot home, as reported by the Colorado Sun. Your number depends on the product and roof. Weigh that against any insurance discount, your local rules and your hail exposure. The free Roof Report shows how often large hail has fallen near your ZIP, and the Colorado climate page explains the hail season.
Sources
- DECRA, Understanding impact resistance (UL 2218)
- Asphalt Magazine, A closer look at roof impact testing
- Professional Roofing (NRCA), shingle impact and wind ratings
- FM Approvals, Standard 4473
- IBHS, Relative impact resistance of asphalt shingles (2014)
- IBHS, Impact-resistant shingle ratings (November 2025)
- GAF, Timberline AS II
- Colorado Roofing Association, Class 3 vs Class 4 shingles
- Colorado Sun, Homeowners insurance discounts and hail mitigation (July 2026)
- Colorado General Assembly, SB26-155 session law
- C.R.S. 10-4-110.8 (homeowners insurance)
- City of Fort Collins, Building Permits
- Larimer County, Roofing requirements
- Boulder County, Class 4 roofing requirement bulletin
- Town of Johnstown, IRC amendments
- Colorado Municipal League, Wildfire and impact-resistant roofing ordinances
- FORTIFIED Home, Hail
- Rocky Mountain Insurance Information Association, Hail
Common questions
Are Class 4 shingles hail-proof?
No. Class 4 means a sample passed a lab test with a 2-inch steel ball. Real hail varies in size, density and angle, and in IBHS's November 2025 testing none of 24 impact-resistant shingles rated Excellent.
Will my insurance company give me a discount for Class 4?
Maybe. Colorado law doesn't require one, and discounts vary by insurer. Ask your agent for the dollar amount in writing before you decide. See insurance in plain English.
Does insurance pay for the upgrade to Class 4?
If your town requires Class 4 on replacements, the upgrade may fall under law-and-ordinance coverage, which Colorado insurers must offer at a minimum of 20% of the dwelling limit. Whether an upgrade is paid otherwise depends on your policy.
How can I tell if my roof is Class 4?
Not by looking. Check your contract, invoice, permit record or a leftover shingle wrapper for the product name and UL 2218 Class 4 listing, then look up the product.
Can I get a state grant for a hail-resistant roof?
Not yet. SB26-155 created grants for FORTIFIED roofs, but the earliest grants are expected in 2027.
What is the difference between Class 3 and Class 4?
Class 3 shingles passed the UL 2218 test with a 1.75-inch steel ball. Class 4 passed with a 2-inch ball, which carries far more energy, about 23.7 ft-lb vs 13.6.
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