The Mil Number on Your Shingle Wrapper Measures One Thing

On the back of a bundle of asphalt shingles, near the product name, there may be a figure printed in mils. Homeowners often read it as a quality score, the way they might read a count on a package. It is a thickness figure and nothing more. A mil is one thousandth of an inch, so the number tells you how thick the shingle is measured to be. It does not tell you how the shingle handles wind, how it resists fire, or how it will hold up over the years on your roof. Those are separate questions, answered by separate tests and printed on separate lines of the wrapper or the manufacturer's sheet.

This page is about what the thickness number is for, what it is not for, and which questions to put to a roofer before the material line on a quote is approved.

Material and spec

Start with the type, because the type explains most of the thickness. A three-tab shingle is a single layer with cutouts that form three tabs per shingle. A laminated shingle, sometimes sold as an "architectural shingle", bonds two layers together so the roof shows depth and shadow lines. Laminated shingles are generally thicker than three-tab shingles, and that difference is real. But thickness is a side effect of how the shingle is built. It is not the test result itself.

Wind performance is the place where homeowners most often read thickness as strength. Wind classification depends on the sealant strip, the way the shingle is nailed, and the test run on the complete assembly. Two shingles of similar thickness can carry different wind classifications, and a thick shingle installed with too few nails or an unsealed tab can perform worse than a thinner one installed to its rated method. If you want the wind rating, the wrapper and the manufacturer's published sheet are where to look. The rating should be named on the material line of the quote, and the crew should be able to point to the same line on the bundle that arrives at your house.

Fire and impact are separate again. A fire classification is a tested rating and is printed apart from thickness. Impact resistance, which is where the Class 4 term comes from, is also tested on its own. A shingle can be thick and still lack an impact rating, and a rating has to be read from the document, not inferred from how the shingle feels in the hand. Each rating line describes one test, and none of them stands in for the others.

Weight is where thickness does matter to the house itself. Heavier shingles add load per square to the deck and the rafters. A laminated product usually weighs more than a three-tab product, and that matters on older framing, on a deck with rot or sag, or on a roof that already carries two layers of old shingles. The weight per square is a structural question, and it belongs with the deck check, not with the appearance of the shingle.

In St. Louis the conditions that test a shingle are the freeze and thaw cycle that lifts edges every winter, the hail that arrives in spring, and the wind that comes through in the storm season. Sealing, nailing, deck condition and the rated classification do most of the work in those conditions. The thickness figure matters less than any of them, and a homeowner who knows what each number measures can see which one a quote is leaning on.

When the bundles arrive, the wrapper is the document to compare with the quote. Check the product name, the type, and each rating line against what is written on the material line. If the wrapper and the quote disagree, the difference should be explained in writing before the crew opens the bundle, not after the shingles are on the roof.

What it costs

Thickness does not set the price by itself. The difference in cost between a three-tab product and a laminated product comes from the material price per square, which is set by the product line, plus labor and the rest of the assembly. A quote that names the shingle product and type lets you compare the same product across bids. A quote that says only "architectural shingle" leaves you comparing different things, and the thickness figure will not close that gap.

Ask for the material line to name the product and the type, and ask whether the square count on the quote matches the square count the supplier will deliver. Underlayment, starter, ridge, flashing and drip edge are separate lines, and each one can change the total. Do not compare one total against another until each line is named in both quotes. Two totals that look close may cover different shingles, different underlayment and different flashing.

If one quote carries a higher material price than another, ask what the higher price buys in measurable terms. Does it buy a stated wind classification, an impact rating, a different construction, or a different sealant arrangement? A bid that cannot say what the extra money buys in rated terms is asking you to trust the price rather than explaining the spec. Ask for the wrapper or sheet for each product so the comparison is made on paper.

Some quotes bundle the material into a single number with no product line at all. That kind of quote is hard to check against the wrapper later, because there is no named product to match. Ask the roofer to break the material out, even if the total stays the same. A named line gives you something to verify when the bundles arrive.

What to ask

Before you accept a shingle on any quote, put these questions in writing and keep the written answers with the rest of your file.

1. What is the exact product name and type on the material line?
2. Does the wrapper for this product print a thickness figure in mils, and where on the wrapper does it appear?
3. What wind classification does this product carry, and what sealing and nailing does that classification assume?
4. Does this product carry a fire classification and an impact rating, and are those named in the quote or only on the manufacturer's sheet?
5. What is the approximate weight per square, and has the deck been checked to carry it?
6. Will you show me the wrapper of the bundle that goes on my roof before the first shingle is nailed?

Keys Roofing can be reached at (314) 220-2333 to talk through the material line before the order is placed. Keep the written answers next to the scope and the photographs, so the product you approved is the product that ends up on the roof.