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Asphalt Roof Shingle Blistering vs. Storm or Hail Damage
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• Asphalt roof shingle blisters and splices, photographs
• Are asphalt shingle rash blisters cosmetic, aesthetic, or a defect?
• Does rash blistering affect shingle life or shingle warranty?
• How to distinguish asphalt roof shingle rash blisters from hail or other storm damage

This website tells readers how to identify & explain roof shingle blistering. Storm damage from wind and hail occur and need to be distinguished from defective asphalt shingle product or asphalt shingle installation errors.

By listing common causes of asphalt roof shingle failures and how to recognize them, building owners and roofing contractors may also be able to reduce the occurrence of asphalt roof shingle storage, handling, and installation errors that affect roof life. Readers are also invited contribute roof failure information to the web author for research purposes. web author for research purposes.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Asphalt Shingle Blisters - Are Shingle Rash Blisters Cosmetic?

Blisters in shingles or "rash blisters" are a cosmetic defect in the opinion of some roofing manufacturers and an indicator of reduced shingle life in the opinion of some building professionals. In the photo shown here, some blister tops have lost granules and are beginning to expose the shingle interior substrate. These Atlas(TM) roof shingles are less than one year old.

Rash blistering considered cosmetic: Atlas roofing has offered reassurance to their customers by indicating that rash blistering is an aesthetic characteristic only. Atlas roofing does not classify blistering as a manufacturing defect. The company has said that rash blistering will not affect the intended performance or life of the shingles and that the shingle warranty will not be affected.

Shingle blistering as a roof defect: although the Atlas view is reassuring, based on field observation and experience (and visible in beginning stages in the photo of an Atlas (TM) roof shingle above), we've seen early granule loss at the blister site. So at least on some roof shingles, rash blisters may indeed be an indication of a reduced-life expectancy.

Some roof inspectors, home inspectors and roofing contractors have observed a shingle wear pattern characteristic of granule loss at the shingle blister sites. Mineral granules at the raised portion of each rash blister can wear off from weather or foot traffic, becoming pits which expose the underlying shingle substrate.

Exposed granule-loss pits on roof shingles increase moisture absorption into the shingle body and in cold climates increase in wear rate from frost. This becomes more apparent when inspecting an older pitted asphalt roof shingle.

Rash blisters on asphalt shingles result from the manufacturing process, (and may be cosmetic or possibly a more serious defect) which are sometimes mistaken for hail damage or other types of asphalt shingle roof wear or damage indicators.

Cosmetic Asphalt Shingle Blister Rash?

This asphalt roof shingle blister pattern is classic "cosmetic shingle blistering" by usual manufacturer description.

Reader Marcia Reid provided these photographs of blisters on an 8 1/2 year old IKO Asphalt shingle roof in Saskatoon, Saskatchewan, Canada. The shingle manufacturer's local representative opined that the blisters were due to tree overhang debris or bird droppings.

What the rep told the owner sounded silly to everyone else: the blistering pattern is just too uniform to be due to a tree or droppings. Besides, as this photo shows, we don't have much in the way of overhanging tree branches at this home.

It is true that we do indeed look at differences in shingle exposure (sun vs shade for example) to explain differences in roof wear. The owner reports that the blistering appears only on the rear slope of the home. We speculated that the blistering shingles were from a common pallet of shingle bundles, perhaps a different one from those used on the front slope.

Unfortunately, on some roofing shingles asphalt shingle bumps or blisters that may appear early in the life of the product or may even be present when the bundle is unwrapped sometimes convert into wear pits when the tops of each blister give up their mineral granules to the weathering process before the remaining area of the shingle. Our photo above shows the beginning of this process.

Each asphalt shingle blister that becomes an asphalt shingle "pit" has exposed the asphalt substrate or mat of the shingle. Where the protective mineral granules are lost from roof shingles wear accelerates and the remaining life of the product shortens at an increasing rate as the shingle begins to absorb water and suffer more in freeze-thaw cycles than before.

This IKO® shingle (photo, above left), (in April 2009) at about 8 1/2 years old, was about 1/3 through the rated life of a 25-year shingle. But if pits and exposure of the shingle substrate appear soon, then the remaining life of this asphalt shingle roof may be less than the rated period. Otherwise, indeed this will have proven to be only a cosmetic concern. We will include future roof condition reports here.

The two photographs of shingle blister rash shown below were provided by reader Jim Todd, a homeowner who commented that both blisters and pitting (where the blister top has ruptured) on these four year old Atlas Chalet™asphalt roof shingles.

At left, oblique sunlight shows blister rash on these asphalt Atlas brand roof shingles. The photo at above right provides a closeup of ruptured shingle blisters, exposing the asphalt shingle mat substrate. Mr. Todd described this blistering pattern as common on several hundred roofs that he has observed, located in Statham Georgia.

Atlas roofing is to be commended for attention client satisfaction: While the reader above reported dissatisfaction with Atlas, in an earlier client letter from Atlas to a concerned homeowner the company and provided to us by that homeowner, Atlas also stated that "in the unlikely event that the rash blistering should negatively affect the intended shingle performance regarding weather protection of the roof, please contact Atlas and we will further evaluate the roof."

So is it aesthetic or not? Perhaps the company is saying "time will tell, But we will stand behind our product warranty." See ROOFING WARRANTIES for general comments on that topic.

Just how much shingle life reduction can be attributed to rash blistering will doubtless remain a debated topic since many factors enter into asphalt shingle life (sun orientation, weather exposure, shingle color, roof slope, nailing, venting, and material quality). OPINION-DF: we figure that the rated life of the shingle is going to be reduced by 5% to 15% based on field observations.

How to Extend the Life of an Asphalt Roof with Shingle Blisters or Shingle Rash

OPINION: you may be able to extend the life of any asphalt roof, including one that has shingle blisters or rash by

• Keep foot traffic on the roof to a minimum. Walking on shingles in hot weather when they are soft easily damages them, especially if you "turn" with weight on your shoe, twisting the shingle surface. Walking on shingles that are blistered, cupped, or curled, or simply brittle with age is likely to damage them. We have tracked the footsteps of some roof inspectors by observing where roof shingle blisters have become wear pits and craters.
• Make sure that your roof is properly vented - a cooler roof lasts longer. If your under-roof ventilation is inadequate, correcting those conditions will extend roof life. See ATTIC CONDENSATION CAUSE & CURE and ICE DAM PREVENTION.
• Proper roof maintenance: in addition to inadequate roof ventilation, repair any roof leaks promptly, keep debris (Debris Staining on Roofs), moss, and lichens off of roofs (MOSS & LICHENS on SHINGLES), and inspect your roof annually for damage that may need additional repair.
• Proper roof installation: once your roof has been installed it's a bit late to "make sure that the roof was installed according to the manufacturer's specifications as well as industry best practices such as nailing pattern and location, proper fasteners, sound roof decking, and shingle layout pattern. Next time.

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

ASPHALT ROOF SHINGLES
  SHINGLE LIFE / WEAR FACTORS
  ASPHALT SHINGLE FAILURE TYPES
  ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES
  BLISTERS on ASPHALT SHINGLES
  CRACKS in FIBERGLASS SHINGLES
  CUPPING ASPHALT SHINGLES
  CURLING ASPHALT SHINGLES
  FISHMOUTHING ASPHALT SHINGLES
  GRANULE LOSS from SHINGLES
  HAIL DAMAGED SHINGLES
  LADDERING & STAIR STEPPING SHINGLES
  MOSS & LICHENS on SHINGLES
  ORGANIC FELT SHINGLE DEFECTS
  SPLICE DEFECTS on ASPHALT SHINGLES
  STAINS on ROOF SHINGLES
  WHAT ARE ASPHALT SHINGLES

• Marcia Reid generously shared her photographs of IKO roof shingle blistering 4/8/2009. Ms. Reed lives in Saskatoon, Saskatchewan.
• Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. (727) 595-4211 mark@BestTampaInspector.com
• Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com
• Arlene Puentes, a licensed home inspector, educator, and building failures researcher in Kingston, NY.
• Jim Todd, provided photographs and description of shingle blister rash on a four year old Atlas Chalet™ shingle roof. 9 July 2009.

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