Guide to Causes of Thermal Splitting or Cracking Asphalt Roof Shingles InspectAPedia® -
Causes & photographs of asphalt roof shingle cracking failures
How to make a shingle warranty claim
Links to Articles on other types & photographs of organic felt asphalt roof shingle failures
Links to Articles on Asphalt roof shingle blisters and splices, photographs
This document tells readers how to identify & explain asphalt shingle cracking or thermal splitting, what causes shingle cracks or splits,
and how to distinguish this product failure (which may be entitled to a warranty or class action claim) from
other roofing product failures or defects.
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"Thermal splitting," or "cracking" which in fact is in most cases actually a
tearing of the shingles is considered by experts to be the principal current
problem with fiberglass-based shingles. We prefer the term tearing as a most
accurate description of what's probably happening. Originally observed on the
lightest-weight (15-year life) shingles this problem has now been found across
all shingle styles, weights (life ratings), and we suspect, probably across
most or all manufacturers of this type of product.
The thermal expansion of defective asphalt shingle product (common in the U.S. across many manufacturers in the early 1990's) followed by thermal contraction when cool weather approached, explained the tear shown in the shingle in our photograph just above.
See THERMAL EXPANSION of MATERIALS for a table of the coefficient of expansion of common building materials. We have not found a source defining the coefficient of thermal expansion of asphalt roof shingles - Contact Us if you can provide that information.
Does Thermal Splitting or Shingle Cracking Tearing Occur only in 3-Tab Asphalt Shingle Roofs?
No. Thermal splitting or tears occur in both conventional 3-tab shingles (photo above) and also in laminated asphalt shingle roofs.
Our photo (below-left) of thermal split/tear damage to a laminated asphalt shingle roof was provided by ASHI Home inspector Steve Mauer.
This unfortunate roof, inspected by Mr. Mauer in 2009, also suffered from granule loss (below-right) that in our OPINION looked like a defective product.
The same roof also included a damaged shingle that looked like a cracking and granule loss problem combined, but we think this was a shingle splice created at the factory during production - a bad individual shingle that is sometimes created when ends of shingle production substrate are spliced together. See SPLICE DEFECTS on ASPHALT SHINGLES
What Does Shingle Cracking or Shingle Splitting Look like?
Watch out: as we warn at ASPHALT SHINGLE FAILURE TYPES if conditions prevented the home inspector from direct access onto the roof or at least a look from a ladder set against the roof edge, shingle damage, cracks, and splits such as that shown in own photo (at left) could have been difficult or even impossible to spot. Inspecting the roof from the ground, even with good binoculars, can't show all roof damage types and conditions.
We have observed a variety of torn or split asphalt roof shingles, illustrated by our photographs below. (Click to enlarge any image.)
Both thermal splitting and other shingle cracks and splits can also occur in a horizontal pattern as we illustrate in our photographs below.
The horizontal cracking occurring in these fiberglass-based asphalt shingles resulted in complete loss of some of the shingles from the roof surface. The silicone caulk was placed by the owner during an attempt to "re-glue" the lost shingle tabs. But using our pen we pointed out additional horizontal cracks and tears developing in the next course of shingles just below. From a the ground the lost shingles looked like an isolated problem. An on-roof inspection told a different story.
What is the Cause of Cracks in Fiberglass-based Asphalt Roof Shingles?
It's possible that shingles made by some manufacturers do not meet the ASTM Standards for tear resistance.
Even where shingles meet the Standards, it's possible that the standards themselves were defective. In particular, for a time the asphalt roof shingle standards combined these concerns:
A thin fiberglass mat was permitted as the shingle substrate, lacking adequate tear resistance
The wind uplift prevention bonding adhesive was too strong, causing the shingles to bond into nearly a single continuous surface that lacked adequate movement to respond to significant changes in temperature without tearing the bound surface
In any case, Fiberglass mat may lack adequate tear resistance
Self-sealing tabs on shingle backs may glue shingles together with too
much strength, causing the roof covering to form a single large membrane which cannot accommodate large temperature changes. This explanation was discovered across the asphalt shingle industry.
Reduced total amount of asphalt in thin fiberglass mats might become brittle after exposure to heat and sunlight
Temperature swings probably contribute to the onset and extent of
tearing, and we'd expect worse tearing where temperature swings are more extreme such as in Northern climates.
Nailing or placement pattern of shingles: "laddering" vs.
"staggered." On laminate and strip type shingles we have inspected roofs on which damage is found occurring at the corners of shingles rather than in
the middle of the shingle material. It appears that as temperatures dropped and the glued-together-roof-membrane cools and contracts, the natural point at
which movement occurs is where shingles are end-butted together.
When the pattern of end-butts is laddered rather than staggered up the roof we have
found corners tearing off of shingles following the laddering pattern exactly. (Laddering is not a recommended installation pattern according to NRCA and
ARMA publications nor according to instructions from some manufacturers.)
Laddering alone cannot be blamed for this failure however, as we have seen
similar shingle tearing following a staggered end-butt pattern up other roofs. However laddering may indeed create a more localized natural point of
separation on a roof, causing most of the movement to occur in a smaller area when the roof material contracts with cooling.
Do Organic Mat Asphalt Roof Shingles Also Crack or Split?
Defective asphalt shingle products of either organic or fiberglass based shingles may experience several failures including cracking, tearing, granule loss, blistering, etc. So, splits or cracks can occur in both organic-mat based and fiberglass-mat based asphalt roof shingles.
Our photo (left) shows a badly worn organic mat asphalt roof shingle with multiple fine cracks throughout its surface. This shingle is worn-out, but the wear pattern is homogenous over the roof slope and in our opinion is a normal wear condition.
Hairline cracks appear in the (generally thicker) organic mat based asphalt roof shingles as a normal sign of aging, and normally late in the life of the roof shingles.
Our OPINION is that a variegated cracking in a somewhat random pattern over the exposed shingle surface is a common age and wear indicator found on older organic based (paper) substrate asphalt shingle roofs.
Nevertheless, fine cracks through roof shingles, regardless of cause, mean accelerating wear rate and on a roof like the one shown at left, the roof needs replacement.
But catastrophic early shingle splitting failures like the ones illustrated earlier in this article were principally a problem of lightweight, fiberglass-mat based asphalt roof shingles made during the period discussed above. Roughly, from 1992 - 1997.
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Additional technical contributors & reference sources for this article are listed below.
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.
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.
Steve Mauer is an ASHI certified home inspector in Doylestown, PA. Mr. Mauer can be reached by email to steve@maurerinspections.com or by telephone at 287-884-4047.
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.
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.
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
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).
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
"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
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Horizontal, vertical, and diagonal tears across multiple strip-type shingles
Horizontal, vertical, diagonal, and corner tears across multiple laminate-type shingles
Both horizontal and diagonal or vertical tearing may occur in the same roof
