Asphalt roof shingle blisters and splices, photographs
Questions & answers about the life expectancy & defects found on organic felt asphalt shingle roofs
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This website tells readers how to identify & explain the most-common asphalt roof shingle failures and
how to obtain asphalt roofing shingle failure claims assistance. These defects occur on organic-mat or fiberglass-mat
asphalt roof shingles.
Common shingle failure factors include
improper storage and handling of the asphalt shingles before installation, improper nailing, improper flashing (which
pertains to any roofing material), and defective asphalt shingle product material leading to thermal splitting,
cracking, blistering, staining, and in some cases curling or cupping shingles.
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.
"Organic felt" roof shingles refers to using cellulose (paper) as the substrate on which the shingle is constructed. The cardboard or cellulose shingle mat is impregnated with hot asphalt and coated with mineral granules to form a sunlight and weather resistant upper surface.
By contrast, at CRACKS in FIBERGLASS SHINGLES we discuss a previous history of thermal splitting of fiberglass-mat-based asphalt roof shingles.
This photograph shows severe loss of mineral granules from an asphalt shingle roof. This roof is way past
needing replacement and is almost certainly leaking. Even a roof with less dramatic granule loss is showing signs of wear
and reduced future life.
Anywhere that a shingle has lost the protection of its mineral granules that
shingle has a reduced life expectancy.
In all climates the loss of granules from an asphalt shingle or mineral-covered roll roofing roof means that area of the roof
shingle has lost its protection from sunlight. In freezing climates, shingle wear may accelerate in the area of lost granules
as the roof ages and is exposed to
freeze thaw cycles.
Once the shingle substrate is exposed by mineral granule loss, that area of the shingle will absorb
more water than its neighbors.
While in this photo the roof is "worn out",
there are several other conditions that can produce mineral loss on asphalt shingle roofs:
Granule loss on a new asphalt roof, loose mineral granules wash down the roof and will appear in gutters and at the ends of downspouts. This is
a normal condition unless it continues and begins to show black exposed roof shingle substrate.
Granule loss on a roof being walked-on: walking on any asphalt shingle roof loosens some of the mineral granules from their
attachment embedded in the asphalt used to impregnate and coat the shingle. If there is a lot of roof traffic, such as when work is
being done on a chimney, you may see "bald" areas of shingles with lost granules where people have been walking. This is damage
caused by workers and is not a product defect.
Granule loss on old asphalt shingle roofs: when an asphalt shingle roof is nearing the end of its life we may see that granules
have begun to wash off of the shingles so as to leave large "bald" or nearly bald areas showing black shingle substrate. These shingles
have more porosity than those where their mineral granules remain in place and may already be leaking even if leaks are not quite visible
in the building interior. Such a roof is ready for replacement.
Granule loss on asphalt shingles due to storms: it is possible that severe weather, such as hailstorms, may damage shingles producing
pitting and granule loss. Such roofs have a reduced remaining life, depending on the severity of damage.
Granule loss due to blistering: blisters or "pimple-like" protrusions from a shingle surface may be
a "cosmetic" manufacturing defect (at least in the opinion of the manufacturers). On at least some roofs we find that these blisters
ultimately become the first wear points on the shingle when their upper surface wears away (perhaps from foot traffic or weather) exposing
small round dots of missing granules on the shingle.
We discuss this defect and how to distinguish between defective shingle product and storm damage at
ASPHALT SHINGLE BLISTERS,
Roof shingle fragility and damage risks
We recommend that inspectors stay off of cupped-asphalt shingle roofs, particularly in cold weather (shingles are more likely to break).
If
we absolutely have to walk on a cupped shingle roof, we would tiptoe carefully, avoiding stepping on the raised or cupped shingle
sections, or if doing repairs, we would prop a ladder up off of the roof surface and work from that scaffold as is sometimes done
with slate or other fragile roof surface repairs.
Is Roofing Felt Underlayment Needed Under Asphalt Roof Shingles?
While the requirement for felt underlayment beneath asphalt roof shingles seems to be a topic of almost timeless argument subject to much arm-waving and little reading of manufacturer's instructions and warranties, various sources recommend or require installation of a felt underlayment over the roof deck before asphalt roof shingles are installed.
Booth & Roberts reported at length on the uses of underlayments on asphalt shingle roofs, citing (quoting):
Asphalt shingle underlays are commonly used throughout North America. The National Roofing Contractors
Association’s (NRCA’s) definition of underlay(ment) includes some important functions:
To separate the roof covering from the roof deck
To shed water
To provide secondary weather protection
The authors point out that
"Resins from green lumber roof decks have been known
to interact with roof shingles, and a separation layer of
underlay can be useful. Underlays are quickly applied and
they can provide temporary roofing before the roof shingles
are installed. Underlays have remained intact after
shingles have blown away, thereby providing temporary roofing [7]. Underlays provide secondary weather protection
in ice-dam situations, when water backs up over the
head-laps of shingles.
Other functions of underlays have been reported [8].
Two of the more important ones are air-flow resistance and
moisture storage. Air-flow resistance reduces windblown
water penetration from the outside and moist air penetration
from the inside of a roof. Moisture storage provides
temporary storage for small amounts of leak water, which
subsequently evaporates in dry weather. We know of no
experiments that quantify these advantages.
There are disadvantages to underlays. Felt materials can
wrinkle and buckle, and these imperfections can telegraph
through the finished shingle layer [8,9]. Peterson reported
that underlays reduced the life of roof shingles in
California due to heat build-up [10]. Explaining how an
underlay will act as secondary weather protection when it
has shingle nails through it every 8 inches (203 mm) or so
can be a challenge. The liquid water transmission test in
ASTM D 4869 for asphalt felt underlayments for shingles
[11] includes the following note: “Take care to ensure that the
staples do not protrude at the front surface of the plywood board so
as not to puncture the test specimen,” this is hardly realistic.
Slipperiness and poor ultraviolet (UV)"
NRCA, Building Code, & Manufacturers Recommend or Require Felt Underlayments on Shingle Roofs
Booth & Roberts also report that [Reference numbers are to references in the cited document.]
NRCA: NRCA recommends underlays on all shingle roof systems
without exception [1]. A 1990 survey indicated that
79 percent of U.S. roofing contractors always used underlays
[12].
Roof Warranty: The absence of underlays can invalidate some
manufacturers’ warranties and roof system fire classifications
[13].
Canadian building codes do not require general (full
roof) underlays under roof shingles. Many Canadian roofing
contractors use general underlays, while others do not.
Typically, underlays are used more over wood plank roof
decks and less over plywood. Underlays are more likely to
be used on lower-sloped roof systems than on steeper
sloped roofs. There also are provincial preferences, for
example, Ontario roofing contractors tend to use underlays
less than their neighbors in Québec.
Inadequacy of Roofing Felt as a Vapor Barrier for Asphalt Shingles in Hot Humid Climates?
A Building Sciences Corporation report also elaborates the usefulness of placing a vapor barrier on the roof deck below shingles in hot humid climates. BSC points out that: [some paraphrasing -DF]
Unvented roofs with asphalt shingles in hot humid climates require a vapor
barrier between the asphalt shingles and the roof deck. This is because asphalt roofing materials
store water from dew or rain. Thus asphalt shingles
form a water reservoir not unlike wood shingle or shake roofs. The report argues that this stored moisture is driven inwards [presumably as water vapor, not liquid water] when sun strikes the damp or wet roof surface, and it continues to argue that moisture is driven through vapor-permeable roofing paper, felt, and plywood or OSB roof decking, thus ultimately into the attic space
But unlike an asphalt shingle roof nailed [over felt] directly to a roof deck, a wood shingle or shake roof that has been installed using best practices includes a disposal path for water absorbed in the roof surface: an air space between the wood roofing and the roof deck, or the installation of wood roofing over spaced nailers or "skip sheathing".
In cool or temperate climates this does not present a problem because the combination of heavy wetting from due or rain i snot combined with solar heating at high outdoor temperatures, say the authors who go on to argue that that buckled roof shingles observed in the morning (caused by moisture migrating back up from the roof deck) relax during the day. But on an un-vented roof moisture driven inwards [through the shingles, roofing felt, and OSB or plywood roof decking] in hot humid climates, needs to be addressed.
This phenomenon can
typically be ignored in climates other than hot humid climates because the combination
of extensive dew formation and solar heating at high outside ambient temperatures is not
common. In vented roofs, this is often manifested in the buckling of shingles early in the
morning as the moisture migrates in to the roof deck sheathing and the joints close. This
is followed by relaxation and opening up of the roof sheathing later in the day—the
buckling disappears.
But in un-vented roofs in hot humid climates, the authors argue that water from the roof surface is drawn upwards in liquid form, by capillary action, between plies of overlapped shingle courses where it passes ultimately through the vapor barrier and through the roof decking to the roof cavity interior.
The driving force of moisture through the roof and into the building is by solar heating according to the authors.
[OPINION-DF: from exterior roof inspections at all times of day and seasons, we have not observed this time-related morning roof shingle buckling in the Northeastern U.S. nor in Florida, nor the Southwest, though the authors report the phenomenon. It is possible that the authors are not quite correct that daily buckling and relaxing of roof shingles can be ignored on a vented roof as harmless, since certainly the product is expected to remain flat, and flexing daily might reduce its anticipated wear life.]
With unvented roof assemblies, this inwardly driven moisture must
be addressed. The preferred method is to prevent the moisture from entering the roof
deck material via the installation of a vapor barrier.
[OPINION-DF: we argue at ROOF VENTILATION SPECIFICATIONS that un-vented roofs are not a best building method in any climate.]
Asphalt shingles are quite impermeable to the passage of liquid water directly through
them. However the geometry of their installation allows wicking at overlaps. This inwardly driven capillary water is the source for the wetting of the
roofing underlayment and roof sheathing. The material properties of shingles change
under elevated temperatures and moist conditions due to their hygroscopic nature. The
large vapor pressures resulting from incident solar radiation and the changed material
properties are sufficient to drive moisture inward through the shingles.
Roofing felts or underlayments vary greatly in their permeability to water vapor; the
typical underlayment used under asphalt shingles in residential construction is quite
permeable.
[QUESTION-DF: we note that the test chamber constructed by BSC was itself in an enclosed, air-conditioned space, and that the underside of the test chamber roof was at least in part exposed to the air conditioning. It seems possible that the reduced humidity and lower temperatures on the "interior-side" of the test roof may have contributed to moisture behaviors that vary from what occurs in the field. Attics and under-roof spaces such as in an un-vented "hot roof" cathedral ceiling are certainly not exposed to cool dry conditioned air. BSC may have addressed this concern but we did not find it in the referenced article.
The conclusion of the BSC report is an argument for installation of an impermeable moisture barrier underneath roof shingles, perhaps in place of the traditional and permeable roofing felt.
[QUESTIONS-DF:
What are the differences between the test roof and a roof's behavior in the field?
How does the impermeable moisture barrier under roof remain impermeable when perforated by shingle nails or staples? What will be the market effects of suggesting entire roofs be underlaid first with a moisture barrier unaffected by roof shingle fasteners such as ice and water shield?
Why not recommend that all roofs and roof cavities include ventilation in their design, not only solving the possible driven-moisture problem discussed by BSC but also providing for longer shingle life (cooler roof surface) and in cooling climates, possibly reduced building cooling costs?]
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Additional technical contributors & reference sources for this article are listed below.
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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.
"Unvented Roofs, Hot-
Humid Climates, and
Asphalt Roofing Shingles
Research Report - 0306
Feb-2003
Building Science Corporation", Building Science Corporation, 30 Forest Street,
Somerville, MA 02143
Quoting from the article abstract:
"When constructing unvented roofs with asphalt shingles in hot-humid climates, a vapor barrier must be
installed between the asphalt shingles and the roof deck." - Web Search 5/21/2010
NRCA Roofing & Waterproofing Manual, 5th Edition, National Roofing Contractors Association, 10255 W. Higgins Road
Suite 600
Rosemont, IL 60018-5607
Telephone: (847) 299-9070 Toll Free: (866) ASK-NRCA (275-6722), e-mail: info@nrca.net. - http://www.nrca.net/rp/pubstore/details.aspx?id=243&c=9
Asphalt roof shingles often show cupping (a concave center), curling (raised edges which curl downwards), and fishmouthing
(raised edge of a shingle tab at its center with little curling). Each of these is discussed below.
Cupping asphalt roof shingles (see photos below), particularly on organic or felt-based asphalt shingles, are a normal wear pattern that shows
up with shingle age.
This "normal" cupping or curling pattern will display shingles which are concave in their center,
with the corners and possibly the three exposed shingle tab edges curled such that the very edge of the shingle curls downwards.
Shingles in this condition are fragile and nearing end of life. In this condition, if someone walks on cupped shingles the raised
cupped sections will break and can lead to early failure and leaks.
Curling roof shingles (see photos below) will show a curling-under at the edges of the shingle tab, first
at the lower edge and sometimes also at the two sides of the shingle tab.
In fact we have seen a "failed" roof that was not leaking until the fellow who was asked to inspect it
walked across this fragile surface.
From a ladder at the roof edge one could clearly see the virtual
footprints of broken shingle edges where the "inspector" had walked. It's best to stay off fragile roof
surfaces to avoid converting a "near end of life" condition to a "failed, leaking" condition.
Curling and cupping may occur together on the same roof, or shingles may appear to be curled-only
(or fishmouth-curled-only as you'll read next). We don't see cupping without some curling.
You may not realize it but asphalt roof shingles are not quite waterproof and in particular the back side of asphalt
shingles is much less water resistant than the upper or exposed side.
The exposed side of an asphalt shingle
is protected from sun damage by a coating of mineral granules.
These shingles rely on the pitch of the roof
and mechanical drainage combined with proper placement or pattern of shingling on the roof to avoid leaks.
[Photo: Carl Gerosa]
Fishmouthed asphalt roof shingles:
An example of the less-waterproof back of asphalt roof shingles is seen below in our photo of "fishmouthed"
roof shingles. In these cases a specific "curling" pattern of shingles called "fishmouthing" is not simple age and wear.
This pattern displays a raised shingle edge (it's not cupped over at the very edge) which, if inspected closely,
will typically occur first and worst over the shingle butt joints where shingle sides abut one another.
Fishmouthed cupping of asphalt roof shingles is caused by excessive under-roof moisture such as by a poorly or un-vented attic or roof cavity.
Moisture escaping through the roof sheathing and up through the bottom of the shingles contacts the uppermost shingle which spans the butt
joint of shingles below, placing more moisture at that point on the shingle tab than elsewhere.
This uneven moisture, probably combined with weather exposure, leads to a raised, cupped "fishmouth" look on those shingles.
The photograph shows a sloppy "ladder pattern" installation of strip-type asphalt shingles. While opinions (and expertise) vary
among roofers, this ladder pattern shingle application may not be as durable a roof installation as one which staggered the shingle offsets more than a
single
six inches (or in this case only 3") left and right with each shingle course.
On other asphalt shingle roofs, particularly older ones,
you may notice that the pattern of fishmouth occurrence on an asphalt shingle roof follows a fairly regular or stair-stepped
pattern, or it may follow a regular "ladder" like pattern up the roof such as is shown in these photographs.
That's because the fishmouthing is occurring at
the butt joints of the shingles where more moisture is passing out of the roof structure into the back side of the shingle
above each butt joint.
You can thus determine the actual pattern in which the shingles were applied to the roof.
"Laddering," while
permitted by some manufacturers and standards, is a less workmanlike shingle installation and may result in a localized early
wear area on a roof. Ladder-pattern shingle application shows that the roofer liked to work up the roof from one position for
as long as possible before moving.
Like cupped and curled asphalt shingles, fishmouthed shingles are also fragile and near end of life and are, as with ordinary cupping, damaged if walked-on.
In some other cases a defective product might cup or curl But we don't have authoritative data on the frequency of that defect.
[Photo of fishmouthed shingles courtesy of Carl Gerosa, New Rochelle, NY.]
Workmanship: Fasteners/Nailing Problems lead to holes or wind blow-off. Notice that not only has
one shingle already fallen or been blown off of the roof, but its neighbors are sliding down. Diagnosis from a photograph is questionable but there appears to be a nailing problem here.
In discussing wind damage to roofing with your insurance adjuster or roofing contractor, be sure to review the details of
original and replacement shingle installation as this can give evidence about the underlying cause of roof failure as well
as informing you of how to avoid roof shingle blow-off in the future.
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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