How To Identify a Manufacturer’s Defect on Composition/Asphalt Shingles

by Jan 22, 2019

Manufacturing defects in asphalt shingles are rare, but they do occur. Material product issues are known to cause some of the most mysterious roof leaks, because these leaks tend to be much harder to track down than the traditional common causes of roof leaks.

When talking about inspecting for manufacturing defects, there are two relevant applications:

    1. Individual shingle defects found during installation
    2. Existing roof with previously-installed shingles that are now performing in a defective manner

This article mostly discusses the latter. Inspecting and identifying material defects on an existing roof is a challenge because (presumably) if the defects were visible during initial installation, they never would have been installed. This means that the symptoms of defective shingles can be subtle, and appear over time. Catching issues early is not only relevant for preventing leaks, but also making sure they are discovered within the material warranty period provided by the manufacturer.

Product defects are rare. For reference, Rhoden Roofing installs over 500 roofs per year, completes 400+ repairs, and inspects roughly 2,500 roofs per year. Of these inspections, fewer than 10 per year involve manufacturing defects.

When they are found, defects on existing roofs range from a few defective shingles to entire sections or slopes of a roof. In our experience, the most common situation to find is sections or individual slopes of a roof, but not the whole house. If individual shingles are different from the rest in the bundle, they are usually identified either at the manufacturing site or during installation and not used. Similarly, it would be exceedingly rare for an entire house worth of shingles to be defective, as opposed to a bundle/few bundles from the same production lot.

Color variances are also sometimes considered manufacturing defects, though this does not impact the performance of the product. Sometimes color variance shingles are sold at a discount or used on outbuildings like a garden shed. For our purposes here, we are talking about consequential product defects that impact the performance of the shingle. For more detail on the components and construction of asphalt shingles, see our article here.

We will discuss how to tell the difference between a manufacturing defect in your asphalt shingle roof and storm damage or normal wear and tear. Our goal is to help you identify the visual signs of an asphalt shingle manufacturing defect. Here are the most common asphalt shingle defects commonly seen in the field:



Asphalt shingles can blister due to poor ventilation, improper installation, and manufacturing defects. The cause can be difficult to assess because the result is the same regardless of the cause. Blistering occurs when moisture becomes trapped under, between, and within a shingle.

If the blistering is due to a manufacturing defect, moisture has been allowed to infiltrate the material and become trapped within the material during manufacturing. When summer heat and UV heat the shingle, the moisture expands, causing a blister. Just with any blister, if popped, it tear will allow moisture and dirt under your roof.

Degranulation (Granule Loss)

Degranulation can occur from a failure of adhesion, impacts, and age. Over time, the asphalt in the shingle will become more brittle due to UV damage, heat, and normal wear. If the granules are coming off due to a manufacturing defect, you can usually spot it because the damage will be similar all over the roof.

Normal wear causes an asphalt shingle to gradually lose granules consistently over the entire roof. If granules are coming loose (but just in certain areas) and your roof is less than two years old, a manufacturing defect more likely caused the problem. The bond between the asphalt and the granules has failed prematurely and will lead to water infiltration of the shingle.

Note that degranulation also occurs during a hailstorm, severe winds, and other natural events. If you are unsure, contact a reputable roofing professional for an opinion before calling your insurance adjuster. Why? More detail here


Craze Cracking

Craze cracking is the result of the outside of the shingle changing in size relative to the inside of the shingle. If the shingle is defective from the factory, the cause is likely a loss of volatiles within the shingle, making the shingle both brittle and less waterproof.

Volatiles are compounds added to asphalt during manufacturing to keep the shingle pliable and waterproof. If too much filler is added to the mix, volatiles can leach out prematurely.  When this happens, the outer surface becomes slightly smaller than the inside. This flexing between the inner and outer layers causes the craze cracking.

Craze cracking causes cracks in the outer surface, which can allow water to penetrate the shingle. Craze cracking can affect the fiberglass mat as well, but craze cracking usually occurs on the top surface of the shingle only, not the entire shingle.


Curling and cupping of an asphalt shingle occurs when the shingle can no longer remain flexible due to UV and heat damage. Over time, the volatiles in the shingle naturally degrade, allowing heat and moisture to bend and twist the shingle.

Often, the shingle stiffens into a cupped or curled position, making those sections much easier to break off. If your shingles begin cupping and curling within the first five years after installation, first check your roof ventilation, then your shingles.

Ineffective attic ventilation causes the shingles to be subjected to heat from both sides of the roof. All manufacturers provide ventilation requirements for their roof materials and they must be followed. The most common cause of asphalt shingle cupping and curling is age and inadequate ventilation of the roof system. 

However, if your asphalt shingle roof begins to cup and curl within the first five years and your ventilation is appropriate, your shingles may be defective.



Can I Use Misshapen or Discolored Asphalt Shingles?

This question comes up in two instances: either during installation when individual shingles have variances from the rest of the ones in the bundle (package), or later during repairs, if a section of roof has become damaged and leftover shingles are available from the original installation.

Just because a shingle has a defect does not make it unusable. Some asphalt shingle defects are purely cosmetic, like being slightly off in color. These shingles are fine to use and will function as intended, although they may not look very good.

Other manufacturing defects however, should be avoided. For example, if a shingle is misshapen it may not align as it should with the shingle above or below it. This can channel water in the wrong direction and allow water under the shingle. Anything affecting the shape or surface (such as cracks) in a shingle should rule it out. During roofing installation; when in doubt, throw it out. Individual shingles are not expensive, and roof leaks are.



Any of the above defects can appear and/or be accelerated due to installation errors including inadequate ventilation of the attic. Shingle damage from wind and hail needs to be distinguished from a manufacturers defect and faulty workmanship to prevent a homeowner from filing an insurance claim when the real issue is a manufacturer’s defect.

If you think you may have roof damage, either from storm or defect, get an opinion about next steps from a reputable local roofing contractor. If you are in the greater Wichita area, you can schedule a free roof inspection with Rhoden Roofing. Rhoden Roofing’s specialists are trained and certified by HAAG Engineering to make the determination between a manufacturer’s defect and hail/wind damage. HAAG Engineering determines the industry standard for what constitutes hail damage versus a manufacturers defect; guidelines followed by roofing contractors, material manufacturers, and insurance companies across the US.

Updated November 2022. 

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