UL 2218 Class 4 Impact Rating: What It Means for Hail
Quick answer
A UL 2218 Class 4 rating is the highest impact-resistance class a roof covering can earn. To pass, a 2-inch steel ball is dropped from 20 feet onto the roofing — the energy of a large hailstone — with no cracking or rupture. Every Interlock aluminum profile is independently certified to Class 4.
What does UL 2218 actually test?
UL 2218 is the North American standard Underwriters Laboratories uses to grade how well a roof covering survives impact — the lab stand-in for hail. A steel ball is dropped from a set height onto the roofing, which is then inspected for cracks, splits, or ruptures that would let water in. The heavier the ball and the higher the drop, the higher the class: Class 1 uses a 1.25-inch ball from 12 feet, Class 2 a 1.5-inch ball from 15 feet, Class 3 a 1.75-inch ball from 17 feet, and Class 4 — the highest — a 2-inch ball from 20 feet. To earn Class 4, the covering is struck twice in the same spot on two separate panels and must show no cracking on either the top or the underside.
Where does Interlock's Class 4 rating come from?
Interlock's aluminum and steel roofing was tested and Listed by Intertek, a global testing and certification body, under UL 2218 (2012 edition). The certification is documented in Intertek's public listing for Delta BP Aluminum and Steel Roof Products, SPEC ID 33876 — Delta Building Products is Interlock's Delta, BC manufacturing operation. The rating covers all four shingle and panel families — Diamond, Shingle & Slate, Shake, and Tile — in both aluminum (3105-H24 / 3003-H24 alloy) and G90 galvanized steel, installed over nominally half-inch APA-rated plywood with a layer of RoofTopGuard II underlayment.
What does Class 4 mean for hail in the real world?
A 2-inch steel ball dropped from 20 feet lands with roughly the kinetic energy of a large, damaging hailstone — the kind that shatters aging asphalt shingles and cracks clay tile. Passing that test with no rupture means an Interlock roof stays watertight through storms that would send a conventional roof to an insurance claim. Aluminum earns the rating by flexing rather than resisting through sheer mass: the deep, textured profile and four-sided interlock spread and absorb impact energy, then return to shape.
Does a Class 4 rating lower my insurance?
Frequently, yes. Because impact-resistant roofs generate fewer hail claims, many home insurers reward them with a premium discount — often reported in the range of 5% to 35%, depending on carrier and state. Several hail-belt states formally recognize UL 2218 Class 4 for roofing credits; the Texas Department of Insurance, for example, maintains a program of impact-resistant roofing discounts. The discount is never automatic — ask your insurer specifically about its impact-resistant or Class 4 roof discount and provide Interlock's UL 2218 Class 4 certificate as documentation.
Frequently Asked Questions
Is Class 4 the highest UL 2218 impact rating?
Yes. UL 2218 has four classes, and Class 4 is the highest. A Class 4 covering must withstand a 2-inch-diameter steel ball dropped from 20 feet — twice in the same spot on two panels — with no cracking or rupture. Every Interlock aluminum profile is certified to Class 4.
Will hail dent an Interlock metal roof?
UL 2218 measures cracking and rupture, not cosmetic denting. Interlock's aluminum panels use a deep, textured profile and a four-sided interlock that absorbs impact energy, so functional hail damage is rare. Class 4 certification means the roof stays watertight and structurally sound after severe hail.
Does a Class 4 metal roof lower my home insurance?
Often. Many insurers offer impact-resistant roofing discounts — commonly 5% to 35% depending on state and carrier — and some states, such as Texas, formally recognize UL 2218 Class 4. Ask your insurer for its impact-resistant-roof discount and provide Interlock's Class 4 certificate.
What is the difference between UL 2218 and FM 4473?
Both rate roof impact resistance on a Class 1–4 scale. UL 2218 uses steel balls dropped from set heights; FM 4473 uses ice balls fired to simulate hail. Insurers accept either, and Class 4 is the top rating under both. Interlock is certified to UL 2218 Class 4.
Sources
- Intertek — Listing SPEC ID 33876 (UL 2218 Class 4) — Delta BP Aluminum and Steel Roof Products
- UL Solutions — UL 2218 Impact Resistance of Prepared Roof Covering Materials — Test standard
- Texas Department of Insurance — Impact-resistant roofing discounts — Insurance credit program
Explore Interlock Metal Roofing
Last reviewed 2026-07-11 · Reviewed by Scott Plumptree, Director of Marketing