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
Questions & Answers about blistering & hail damage on roof shingles

This article explains how to identify & explain roof shingle blistering or "blister rash" on asphalt roofing. Storm damage from wind and hail occur and need to be and can be distinguished from defective asphalt shingle product or asphalt shingle installation errors.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.

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.

Also see GRANULE LOSS from SHINGLES (all causes of granule loss) and see HAIL DAMAGED SHINGLES where we describe how we distinguish between blister damage and hail damage to asphalt roof shingles. Readers are also invited contribute roof failure information to the web author for research purposes. web author for research purposes.

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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.

Causes of Shingle Blisters & Blister Rash on Asphalt Roof Products

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.

Solvent-caused shingle blistering? Shingle blisters might be caused as well by excessive use of roofing mastic or additional adhesives that are applied during or after roof installation. A warning to this effect issued by GAF Materials Corporation is found at WIND DAMAGE to ROOFS.

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.

Asphalt shingle blisters on Atlas Chalet shingles 4 years old (C) Daniel Friedman Jim todd

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. Close ups of the photo at right are also found at HAIL DAMAGED SHINGLES.

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.

Questions & Answers about blistering & hail damage on roof shingles

Question: could hail damage to roof shingles lead to later shingle rash or shingle blisters?

Thank you for your web site and all the information you provide!!! I have done some research on hail damage and blistering.

I was wondering if it would be reasonable to suggest that hail damage [see HAIL DAMAGED SHINGLES] could be a cause of blistering? Seems blistering requires some sort of initiating cause such as manufacture defect or moisture. And, appears some hail damage is quite small, only the removal of few granules and possible underlying asphalt leaving behind a small void. Could moisture then get absorbed into the shingle? And later cause blistering?

I have lived in both AZ and N. TX. Hail occurs more frequently in TX. And, roof in AZ undoubtedly get hotter than in N. TX. But I didn't find that blistering (of asphalt shingles) was much of a problem in AZ. The examples found seem to be in areas which are more prone to hail. So, this is pushing me to believe that hail could be causing the blistering in many cases. What do you think? - B.S.

Reply:

I have not thought about hail damage as causing blistering but you raise an interesting question about the possible causes of that shingle anomaly.

My OPINION has been that blistering or shingle rash starts as a manufacturing artifact, a bumpy shingle surface that is caused by the manufacturing process itself - perhaps the shingle granules are clustered or stuck together, or perhaps there are temperature variations that cause bubbles or just lumps in the asphalt on the shingle substrate to which the granules are applied. But I do not know - and I bet the manufacturers know exactly how this is happening.

There is no doubt that we see blistered or rashed shingles that come out of the bundle, new, from the factory in that condition. And manufacturers generally opine that it's a cosmetic only condition - a viewpoint with which I do not always agree.

But you raise the interesting question of whether or not hail impact could cause a more subtle damage to shingles that leads to a second type or source of shingle blistering.

That explanation doesn't match with the close-up examination I've made of some hail damaged roofs on which I saw that granules are dislodged or scoured off of the shingle surface. But I grant that an impact that leaves granules in place could have the more subtle effect you suggest: a loosening or opening of the granule surface to allow water and perhaps freezing impact on the shingle surface.

To investigate the question in a more credible and scholarly way would involve at least dissecting some hail impacted asphalt roof shingles. We'd cut the shingle in cross section and make microscopic examination of the cross section for visual evidence of changes in the material - as a start. Even more subtle effects of hail impact on the adhesive properties of the shingle surface, adhering granules to the asphalt substrate, could be present and would require a more technical, perhaps chemical analysis to observe.

Frankly I don't think the hail as previously un-recognized source of shingle blisters explanation sounds very likely. Conversely, there is sufficient (size, mass, velocity, angle of impact) hail damage to an asphalt shingle roof that was already blistered, I would expect the blisters to play a role in the subsequent hail damage or roof wear that would be observed.

But it's worth taking a closer look at your hypothesis by examining some representative shingles microscopically and by asking shingle manufacturers for their opinion. Let's pursue it. - Editor

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ASPHALT ROOF SHINGLES
  ASPHALT SHINGLE DEFINITIONS
  ASPHALT SHINGLE FAILURE TYPES
  ASPHALT SHINGLE INSTALLATION
  ASPHALT SHINGLE LIFE / WEAR FACTORS
  ASPHALT SHINGLE PROPERTIES
  ASPHALT SHINGLE RE-ROOF GUIDE
  ASPHALT SHINGLE UNDERLAYMENT SPECS
  ASPHALT SHINGLE VALLEY FLASHING
  ASPHALT SHINGLES on VERY STEEP ROOFS
  ALGAE, FUNGUS, LICHENS, MOSS COMPARED
  ALGAE STAINS ON ASPHALT ROOF SHINGLES
  ALGAE STAIN TEST METHODS
  ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES
  BLACK STAIN REMOVAL & PREVENTION
  BLISTERS on ASPHALT SHINGLES
  CRACKS in FIBERGLASS SHINGLES
  CUPPING ASPHALT SHINGLES
  CURLING ASPHALT SHINGLES
  EARLY ASPHALT SHINGLE FAILURE
  EXTRACTIVE BLEEDING on SHINGLES
  FISHMOUTHING ASPHALT SHINGLES
  GRANULE LOSS from SHINGLES
  HAIL DAMAGED SHINGLES
  LADDERING & STAIR STEPPING SHINGLES
  LIFE / WEAR FACTORS in SHINGLES
  MECHANICAL DAMAGE of SHINGLES
  MOSS & LICHENS on SHINGLES
  ORGANIC FELT SHINGLE DEFECTS
  SPLICE DEFECTS on ASPHALT SHINGLES
  STAINS on ROOF SHINGLES
  WHAT ARE ASPHALT SHINGLES
  WIND DAMAGE to ROOFS

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.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.

Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
The Journal of Light Construction has generously given reprint permission to InspectAPedia.com for this article. All rights and contents are ©Journal of Light Construction and may not be reproduced in any form.
Architectural elements: the technological revolution: Galvanized iron roof plates and corrugated sheets; cast iron facades, columns, door and window caps, ... (American historical catalog collection), Diana S Waite, available used out of Amazon.
Asphalt Roofing Residential Manual,
Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF] ISBN-10: 0471331724 ISBN-13: 978-0471331728
Building Pathology: Principles and Practice, David Watt, Wiley-Blackwell; 2 edition (March 7, 2008) ISBN-10: 1405161035 ISBN-13: 978-1405161039
Built-Up Roof Systems, Manual, C.W. Griffin, Mcgraw-Hill (Tx); 2nd edition (July 1982), ISBN-10: 0070247838, ISBN-13: 978-0070247833
Concrete Folded Plate Roofs, C. Wilby PhD BSc CEng FICE FIStructE (Author), Butterworth-Heinemann, 1998, ISBN-10: 0340662662, ISBN-13: 978-0340662663
Concrete Shell Roofs, C. Wilby PhD BSc CEng FICE FIStructE (Author),
Concrete Dome Roofs (Longman Concrete Design and Construction Series),
Concrete Roofing Tile, History of the, Batsford, 1959, AISN B000HLLOUC (availble used)
Copper Roofing, by CDA
Copper Roofing, Master specifications for copper roofing and sheet metal work in building construction: Institutional, commercial, industrial, I.E. Anderson, 1961 (hard to find)
Corrugated Iron, Building on the Frontier, Simon Holloway
Green Roof Plants: A Resource and Planting Guide, Edmund C. Snodgrass, Lucie L. Snodgrass, Timber Press, Incorporated, 2006, ISBN-10: 0881927872, ISBN-13: 978-0881927870. The text covers moisture needs, heat tolerance, hardiness, bloom color, foliage characteristics, and height of 350 species and cultivars.
Green Roof Construction and Maintenance, Kelley Luckett, McGraw-Hill Professional, 2009, ISBN-10: 007160880X, ISBN-13: 978-0071608800, quoting: Key questions to ask at each stage of the green building process Tested tips and techniques for successful structural design Construction methods for new and existing buildings Information on insulation, drainage, detailing, irrigation, and plant selection Details on optimal soil formulation Illustrations featuring various stages of construction Best practices for green roof maintenance A survey of environmental benefits, including evapo-transpiration, storm-water management, habitat restoration, and improvement of air quality Tips on the LEED design and certification process Considerations for assessing return on investment Color photographs of successfully installed green roofs Useful checklists, tables, and charts
Handbook of Building Crafts in Conservation, Jack Bower, Ed., Van Nostrand Reinhold Company, NY 1981 ISBN 0-442-2135-3 Library of Congress Catalog Card Nr. 81-50643.
Historic Preservation Technology: A Primer, Robert A. Young, Wiley (March 21, 2008) ISBN-10: 0471788368 ISBN-13: 978-0471788362
Historic Slate Roofs : With How-to Info and Specifications, Tina Skinner (Ed), Schiffer Publishing, 2008, ISBN-10: 0764330012 , ISBN-13: 978-0764330018
Low Slope Roofing, Manual of, 4th Ed., C.W. Griffin, Richard Fricklas, McGraw-Hill Professional; 4 edition, 2006, ISBN-10: 007145828X, ISBN-13: 978-0071458283
- Roof failure causes in depth (and specific methods for avoiding them)
- Roof design fundamentals and flourishes, based on voluminous industry research and experience
- New technologies and materials -- using them safely and correctly
- Comprehensive coverage of all major roofing systems pecifications, inspection, and maintenance tools for roofing work
Metal Roofing, an Illustrated Guide, R.A. Knowlton , [metal shingle roofs],
Patio Roofs, how to build, Sunset Books
Problems in Roofing Design, B. Harrison McCampbell, Butterworth Heineman, 1991 ISBN 0-7506-9162-X (available used)
Roofing The Right Way, Steven Bolt, McGraw-Hill Professional; 3rd Ed (1996), ISBN-10: 0070066507, ISBN-13: 978-0070066502
Slate Roofs, National Slate Association, 1926, reprinted 1977 by Vermont Structural Slate Co., Inc., Fair Haven, VT 05743, 802-265-4933/34. (We recommend this book if you can find it. It has gone in and out of print on occasion.)
Roof Tiling & Slating, a Practical Guide, Kevin Taylor, Crowood Press (2008), ISBN 978-1847970237,
If you have never fixed a roof tile or slate before but have wondered how to go about repairing or replacing them, then this is the book for you. Many of the technical books about roof tiling and slating are rather vague and conveniently ignore some of the trickier problems and how they can be resolved. In Roof Tiling and Slating, the author rejects this cautious approach. Kevin Taylor uses both his extensive knowledge of the trade and his ability to explain the subject in easily understandable terms, to demonstrate how to carry out the work safely to a high standard, using tried and tested methods.
This clay roof tile guide considers the various types of tiles, slates, and roofing materials on the market as well as their uses, how to estimate the required quantities, and where to buy them. It also discusses how to check and assess a roof and how to identify and rectify problems; describes how to efficiently "set out" roofs from small, simple jobs to larger and more complicated projects, thus making the work quicker, simpler, and neater; examines the correct and the incorrect ways of installing background materials such as underlay, battens, and valley liners; explains how to install interlocking tiles, plain tiles, and artificial and natural slates; covers both modern and traditional methods and skills, including cutting materials by hand without the assistance of power tools; and provides invaluable guidance on repairs and maintenance issues, and highlights common mistakes and how they can be avoided. The author, Kevin Taylor, works for the National Federation of Roofing Contractors as a technical manager presenting technical advice and providing education and training for young roofers.
The Slate Roof Bible, Joseph Jenkins, www.jenkinsslate.com, 143 Forest Lane, PO Box 607, Grove City, PA 16127 - 866-641-7141 (We recommend this book).
Slate Roofing in Canada (Studi4es in archaeology, architecture, and history),
Smart Guide: Roofing: Step-by-Step Projects, Creative Homeowner (Ed), 2004, ISBN-10: 1580111491, ISBN-13: 978-1580111492
Solar heating, radiative cooling and thermal movement: Their effects on built-up roofing (United States. National Bureau of Standards. Technical note), William C Cullen, Superintendent of Documents, U.S. Govt. Print. Off (1963), ASIN: B0007FTV2Q
Tile Roofs of Alfred: A Clay Tradition in Alfred NY
"Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
Wood Shingle Roofs, Care and Maintenance of wood shingle and shake roofs (EC), Stanley S. Niemiec (out of print)
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Asphalt Shingle Blisters - Are Shingle Rash Blisters Cosmetic?

Causes of Shingle Blisters & Blister Rash on Asphalt Roof Products

Cosmetic Asphalt Shingle Blister Rash?

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

Questions & Answers about blistering & hail damage on roof shingles

Question: could hail damage to roof shingles lead to later shingle rash or shingle blisters?

Reply:

Questions & Answers regarding this article

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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair