Guide to Causes of Thermal Splitting or Cracking Asphalt Roof Shingles
CRACKS in FIBERGLASS SHINGLES - CONTENTS: 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
POST a QUESTION or READ FAQs about asphalt roof shingle splits, cracks, and thermal splitting: effects on roof life, leaks, warranty coverage, cause, history of product problems
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Asphalt shingle cracks due to thermal splitting & defective product: 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.
"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 Thermal Splitting Cracks in Fiberglass-based Asphalt Roof Shingles?
Our photos above demonstrate two classic thermal split patterns in fiberglass based asphalt shingles: vertical splits running straight up the roof (above left) and diagnoal splits following butt joints (above right).
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.
Splits or Cracking in Organic Asphalt Shingles
Organic mat asphalt shingles also may show cracking and accompanying granule loss. 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.
But thermal splitting is particularly a problem with fiberglass mat based asphalt roof shingles. The 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.
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.
Cracking due to cold weather installation & bending ridge or hip cap shingles: see RIDGE & HIP CAP SHINGLES for additional discussion of distinguishing cracking wear failures from other types of shingle failures.
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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.
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Useful checklists, tables, and charts
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
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