Synthetic Slate and Shake: How Composite Roofing Compares

Synthetic slate and shake are molded composite products made to look like natural stone or split cedar. Choose one on its fire class, its impact rating and its data-sheet weight, because a long warranty covers only the defects it lists and is not proof the roof will last that long.

The comparison that matters is composite against the real material it imitates, on the same documents. If you are still choosing between composite and materials it does not imitate, start with the overview of every roofing material.

What Synthetic Slate and Shake Are

Composite roofing is made in molds, so each piece comes out with a slate’s edge and texture or a shake’s split grain without being quarried or sawn. Formulations differ from maker to maker and from one product line to the next. The product data sheet is the only reliable description of what you are buying, so ask for it before you compare anything else.

Two points follow for a buyer. First, the product’s performance comes from its formulation and its testing, not from the material it copies, so natural slate’s or cedar’s track record tells you nothing about it. Second, the product is newer on roofs than the materials it imitates, which makes its documents more important than its looks.

Here is what to request from each option, side by side:

Ratings to Ask For: Fire, Impact, and Wind

Fire. Roof fire classes are set under ASTM’s E108 fire tests of roof coverings, in edition E108-25 (active as of 2026): Class A covers severe fire test exposure, Class B moderate and Class C light. The class belongs to the assembly that was tested, which can include a specific underlayment or deck. A brochure that says “Class A” without naming the assembly does not tell you whether your installation will match it. Ask for the listing and install exactly what it names.

Impact. Two test families apply. UL 2218 is the Standard for Impact Resistance of Prepared Roof Covering Materials, in Edition 2 (2022, revised May 2024); it aims steel balls at the most vulnerable points of a test assembly, the largest of them 2.00 inches across for Class 4, according to IBHS’s summary of UL 2218 impact tests. FM Approvals’ ANSI/FM 4473 ice-ball standard uses freezer ice balls from 1-1/4 to 2 inches, and its scope is new rigid roofing materials, with slate and tile among its examples. A flexible composite may fit one standard better than the other, so ask which standard the product was tested to and what class it earned, and read the class only within that standard.

Do not borrow ratings from other products. IBHS’s impact ratings cover asphalt shingles, and a composite’s maker cannot claim them by resemblance.

Wind. The familiar shingle wind classes, ASTM D3161 and D7158, are tests written for asphalt shingles. Ask the maker which wind test the composite was evaluated under, at which fastener count and pattern, and make sure the installer’s fastening matches that test.

Code approval. Ask your building department how it approves the product and whether it needs an evaluation or approval document on file. Get a copy before the permit is issued, not after the crew arrives.

Weight: Check the Number Behind the Lighter-Roof Pitch

Weight is the reason composite comes up as an alternative to natural slate, so verify it rather than accept it. For the materials composite is measured against, a building-material weight table published by Boise Cascade from ASCE 7-16 data gives slate at 7 pounds per square foot (psf) for 3/16-inch stone and 10 psf for 1/4-inch, wood shingles at 3 psf and asphalt shingles at 2 psf.

Put the composite’s data-sheet weight next to those numbers and next to whatever is on your roof now. If the composite weighs the same as or less than your current roof, the structural question narrows to the deck and fasteners. If it weighs more than your current roof, even if it weighs less than real slate, the framing check for a heavier covering applies.

What a Long Warranty Does and Doesn’t Prove

A manufacturer’s warranty promises repair of leaks from the causes it lists and no others, as the National Roofing Contractors Association’s consumer bulletin on roof system warranties explains. NRCA’s warranty resources page also notes that manufacturer coverage periods range from 20 years to a lifetime. The length tells you how long the promise runs; the list of covered causes tells you what the promise is.

A warranty is a contract, not a field record. A product that has been on roofs for a short time can carry a lifetime warranty because the warranty’s terms, exclusions and proration limit what the maker will pay. Read the full document, not the brochure summary, and check:

• What is covered: manufacturing defects only, or leaks too, and whether labor and tear-off are included.
• How coverage declines: any proration schedule, and when it starts.
• What voids it: installer requirements, registration deadlines, accessories that must come from the same maker.
• Who can claim it: whether it transfers to a buyer if you sell.

Our guide to roof warranties explains manufacturer versus workmanship coverage in more depth. For track record, ask the maker how long this specific product version has been on roofs in a climate like yours, and ask the installer for addresses of roofs several years old that you can look at from the street.

How Close the Look Gets

From the street, composite slate and shake can pass for the real thing. Up close, differences show in edge thickness, surface texture, color variation across the roof, and how the color holds up over time. None of that shows in a brochure photo.

Ask for a full-size sample board, look at it outdoors in daylight next to your siding and trim, and visit a roof with the same product that has weathered for a few years. If you are matching a neighbor’s natural slate or cedar, hold the sample against that roof’s color from the same distance a passerby would see it.

Think ahead to the first repair. If a few pieces break years from now, the patch needs the same product, version and color, and a molded product line can change or be discontinued. Ask the maker how long it supplies replacement pieces for a color it has dropped, and ask the installer to leave a few spare pieces from the same production run with your roof records.

Composite or the Real Material?

Let the documents and the house decide, in this order:

• If a historic district board requires the original material, composite may not be approvable; ask the board before pricing it. Our guide to historic roof rules explains the review.
• If the framing cannot carry natural slate, composite is a candidate, but only at the data-sheet weight you have verified against your current roof.
• If your town, HOA or insurer requires Class A, treated cedar’s Class B and C labels fall short, and composite shake becomes worth pricing, but only with a Class A listing for the assembly you will install. Compare it against cedar shakes and shingles on that listing.
• If you plan to own the house for decades and the framing allows it, natural slate has the longer documented record; industry sources put grade S1’s expected service life at more than 75 years, as explained in natural slate roofs.
• Where hail is the hazard that matters most, rank impact classes only within the same standard. A composite tested under UL 2218 and a natural slate tested under FM 4473 cannot be ranked against each other by class number alone, so ask for results under the same test where you can.
• If you choose composite, prefer the product with the longest record of installations you can see in person.

Before signing, collect four documents: the fire-class listing with its tested assembly, the impact class with its standard, the weight per square foot, and the full warranty. If any one is missing, the bid is not ready to accept.

This guide is general information for U.S. homeowners, not legal, insurance, tax, or engineering advice. Codes, laws, and policy terms vary by location and change over time; confirm details with your local building department, your insurer, or a licensed professional.

Sources

• E108 Standard Test Methods for Fire Tests of Roof Coverings (E108-25), ASTM International
• UL 2218 Standard for Impact Resistance of Prepared Roof Covering Materials, UL Standards & Engagement
• Relative Impact Resistance of Asphalt Shingles: Summary of UL 2218 Impact Tests, Insurance Institute for Business & Home Safety
• ANSI/FM 4473: Impact Resistance Testing of Rigid Roofing Materials by Impacting with Freezer Ice Balls, FM Approvals
• Weights of Building Materials (Tech Note GE-1), Boise Cascade Wood Products
• Roof System Warranties (Consumer Advisory Bulletin Issue 1), National Roofing Contractors Association