Two Wind Ratings on Your Shingle Wrapper, and What Each One Tests

A shingle wrapper prints a wind number, and most homeowners read it as one promise. In practice the number comes from one of two ASTM test methods, and they do not measure the same thing. Before you accept a quote that names a shingle, it helps to know which test produced the number, what the number means for a St. Louis roof, and what the install has to do for the rating to mean anything.

Material and spec

ASTM D3161 is the older of the two. It drives air across a shingle sample at increasing speeds and checks whether the tabs or the shingle edges lift or tear free. Its classes are A, D and F. Class A is tested to 60 miles per hour, Class D to 90, and Class F to 110. The sample is sealed and nailed under the test conditions, so the result describes how the product holds when it is installed correctly, not how a particular roof will hold on the day of a storm.

ASTM D7158 is a different method. It measures uplift resistance of the shingle assembly, and its classes are named D, G and H. Those letters correspond to basic wind speeds of 90, 120 and 150 miles per hour. Because the method is tied to a design wind speed, a D7158 class tells you the wind load the shingle was tested to carry under the standard's assumptions. The two systems are not interchangeable. A wrapper that says Class F under D3161 and a wrapper that says Class H under D7158 both carry a rating, but a homeowner comparing two quotes needs to know which letter system is in front of them.

Neither test is a guarantee for an installed roof. Both assume the shingle is nailed where the manufacturer's instructions say, with the correct fastener count and placement, and that the sealant strip has bonded. The edges, the rakes and the ridge see the highest uplift on most roofs, so the starter course and the hip and ridge pieces carry as much of the load as the field shingles do. A rating printed on the bundle does not rescue a roof that was nailed high, nailed short of the count, or left with the starter out of line. The printed number describes the product. The install decides whether your roof gets that product's performance.

For a St. Louis homeowner the practical question is which rating the shingle you are buying carries, and whether the quote names it. Most quotes name the product line and the color. Fewer name the wind class. If the wind class is not on the quote, you cannot compare two bids on it, because nobody has written it down.

Check the wrapper on the bundles when they arrive. The rating is printed on the packaging alongside the product name. Read it against the quote before the crew starts. If the bundles on the truck carry a different product name or a different rating from the one you agreed to, that is a material change, and it belongs in front of the homeowner before the first bundle is opened.

What it costs

A higher wind class is usually a product decision, not a labor decision. The crew installs the shingle the quote names, so the difference between a standard product and a higher rated one sits in the material line. It is not a separate charge for wind. A quote that lists one shingle price for the whole roof does not tell you whether that price covers the higher class or the base class. Ask which.

Two quotes can look nearly identical on the total and still differ in material. One may name a product with a D3161 Class F rating and the other may name a product with no stated wind class at all. The totals will not show that. The line item will, if the product is named. This is one reason to read the material line first and the total second.

A higher rating is also not a reason to buy a spec the roof does not need. The right class depends on where the roof sits, how exposed it is, and what the building was designed to carry. Ask the roofer to state in writing which class they are quoting and why. A useful answer names the product and its rating together, and does not leave the wind number as a sales phrase.

What to ask

• Which product is named on the quote, and which wind test does its rating come from?
• Is the wind class printed on the wrapper of each bundle, and will the crew install the product that matches the quote?
• Does the written scope list the nailing count and the starter course, since those decide whether the rating applies to your roof?
• If the bundles on the truck differ from the quote, who approves the change before anything is installed?

Ask Keys to put the product name and the wind class in the written scope before the start date is set, with photos of the bundles when they arrive. The office number is (314) 220-2333.