Causes of Wear or Leaks in Asphalt Shingle Roofs
InspectAPedia® -
Causes of asphalt roof shingle wear and failure
Causes of leaks in asphalt shingle roofs
What affects the life expectancy of an asphalt shingle roof?
What building factors also affect roof shingle life?
What is the cost-effectiveness of asphalt roof shingles versus other roof coverings?
This document describes most of the factors which determine the life expectancy of an asphalt shingle roof - "roofing shingle wear factors".
These wear factors affect most asphalt roof shingle types, whether organic felt based or fiberglass fabric based, and whether
the shingle type is "cutout" or three-tab, strip-type, or a laminate-type roof shingle.
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.
This article is part of our series on inspecting, diagnosing, installing and repairing Asphalt Roof Shingles which tells readers how to identify & explain the most-common asphalt roof shingle failures. 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.
SHINGLE LIFE / WEAR FACTORS for Asphalt Shingle Roofing Products
While the historical cost-performance of this product has been good in most cases, durability issues and wear-out or material failures occur earlier than expected in some situations.
The expected life of a roof covering depends on many variables including:
Asphalt Shingle Quality: type, quality, thickness, shingle design (cutout 3-tab versus laminated) and rated or design-life of roofing material selected
Asphalt Shingle Color: in hot sunny climates lighter colors tend to resist sunlight damage and last longer.
Roof Shingle Age: the shingles in the photo at the top of this page are organic based asphalt (asphalt-impregnated paper coated with mineral granules) at or near the end of their life.
Typical life expectancy for roofing products can vary widely as a function of the material composition, type, installation details, and other factors
discussed in depth at this website. Typical shingle life expectancies range from about 15 years to 40 years.
Sunlight and Heat Effects on Asphalt Shingles: Storing shingles in hot sun makes them stick together, making damage
likely as they are pulled out of their bundle.
Cold and Freezing Effects on Asphalt Shingles: Storing shingles in freezing conditions increases the chances that a shingle will crack when being used if applied
in cold weather, especially ridge cap shingles which break when bent. We used to cut those and then leave them inside on a radiator until needed.
Rain Effects on Asphalt Shingles: believe it or not, shingles are not quite waterproof and depend on roof slope to shed water effectively. Shingles that are left
exposed to rain and then installed may violate the manufacturer's warranty and may fail early, possibly due to the effects of temporarily trapped
moisture at the time of application. We have found sections of asphalt shingle roofs all showing early wear traceable to a specific bundles of asphalt
shingles that were at the top of the stack and exposed to the weather. This photo shows the effects of rain on shingles when the
bundles were left outside for some time before use.
Stacking Shingles in Storage: shingles should not be stored at the supplier nor at the job site stacked higher than two pallets. If shingles
need to be stacked higher, separator boards or plywood are needed under each pallet to protect the shingles below from damage by the weight and
edges of the pallet and shingles stacked above. We've seen shingle pallets eight-high with no inter-pallet protection at HG Page Lumber in Poughkeepsie
and at an occasional Home Depot. But don't try giving the supplier your personal advice about how to stack their product, you'll just annoy them. Inspect
and reject visibly damaged shingle bundles and hope that there are not more subtle damage effects not visible at first sight.
Bending Asphalt Shingle Bundles: roofers like the shingle bundles to get up on the roof by magic - by a special loader or carried up by an
assistant. A smart assistant spreads the bundles out over the roof to avoid too much weight in one place (point-load structural failures).
But especially on a steep pitch roof, some "experts" put all of the bundles of shingles across the ridge. Bending shingles over the ridge,
especially in cold weather, may violate the manufacturer's warranty and may damage the shingles, including subtle damage that appears after
installation as early cracks, tears, or failures. Reference: http://www.owenscorning.com/around/roofing/specs/Classic-C.pdf from Owens Corning cites
their requirements for handling and storing shingles.
Asphalt shingles should be stored: flat, in un-opened bundles with labels intact and legible, in cool, not freezing and not hot temperatures (under 110 degF.),
under cover, protected from the weather, protected from damage by stacking more than two pallets high, and kept that way until they are ready for use.
Asphalt roof shingles should be delivered: in flat, un-damaged, un-opened bundles, protected at the job-site (as described above), and
when moved to the rooftop, shingle bundles should be laid flat, not over the ridge, and should not be placed with too much weight in locations that
may damage the building structure.
Building factors affecting asphalt shingle roof life:
Roof slope: On what degree of roof slope can asphalt shingles be installed? - According to the National Roofing Contractor's Association (NRCA) and the Asphalt Roofing Manufacturers' Association (ARMA) roofing guidelines, conventional roof shingles should not be used on slopes less than 3 in 12 - that is 3" of rise in 12" of run on a roof slope.
If asphalt roof shingles must be applied on such a low slope, say for aesthetic reasons, they're installed as a cosmetic applause on top of a nailable waterproof membrane, or laminated with courses of sealing membrane between every shingle course (costly and still a bit risky). We discuss roof slope in detail atASPHALT SHINGLE INSTALLATION
Roof problem areas due to roof shape & building design. Examples are complex roof shapes that make under-roof venting difficult or unfortunate architecture that places obstructions such as a wall or a chimney right in a roof valley, or causes other shapes which interfere with good roof drainage. (Shingles depend on slope and drainage to avoid roof leaks).
Sun exposure: orientation some roof slopes towards sunlight can cause faster wear on those slopes than on shaded roof slopes
Roof Ventilation: attic or under-roof ventilation. Un-vented roofs, especially in sunny hot climates, stay at a higher surface temperature and can be expected to have a shorter life. Roof ventilation is discussed in detail atROOF VENTILATION SPECIFICATIONS.
Technical material composition and asphalt shingle design details (roofing material components, manufacturing process, wind-uplift prevention). We compare types of asphalt shingles atASPHALT SHINGLE PROPERTIES
Marketing and economic considerations (aggressive sale of new roofing material by some contractors, reluctance to or economic reasonableness of patching damaged areas on older roofs)
Manufacturing Defects and Asphalt Shingles: even the best manufacturers are at risk of episodes of producing a defective product. The asphalt shingle
manufacturing line is a challenging environment where variations in control of the process can produce a defective product with a reduced life. The thermal
splitting failure discussed at this website is an example of a widespread fabrication defect that affected many asphalt shingle manufacturers. See
CRACKS in FIBERGLASS SHINGLES SPLICE DEFECTS on ASPHALT SHINGLES STAIN DIAGNOSIS on ROOFS
Weather and Weather Exposure: variations in climate and other local weather conditions affect roof shingle life
Wind Effects on Roofing: exposure to damage (wind, tree limbs, hail, snow, ice, foot traffic).
Key in wind blow-off of asphalt shingles is whether or not the shingles were properly installed, especially properly nailed according to the manufacturer's recommendations. Also on occasion a brand
new roof that has not had a chance for its self-sealing adhesive to work may blow off in windy conditions even if it was nailed properly. Review the workmanship defects below as a number of them constitute
improper nailing and can cause a wind failure of roofing that may otherwise may be misdiagnosed. Shingle wind damage details are atWIND DAMAGE to ROOFS.
Nailing of Asphalt Shingles: asphalt shingle roof nailing errors: improper nailing pattern, omitted nails, too many nails, nails not properly placed
in the shingle, and lazy use of the roofing nailing gun: nailing without moving on the roof, leaning out too far, making nails
enter the shingle on an angle so that the nail head cuts the shingle; failure to set nails properly (too deep - cuts shingle,
too shallow, cuts shingle above).
The older roof nailing guns that used staples required even more careful use of that tool. If the
roof shingle staple was driven too deeply it cut the shingle and it would blow off of the roof. If the shingle was left too high
or canted (lazy-leaning out too far again) the protruding staple cut the overlapping shingle above. Shingle nailing details are atASPHALT SHINGLE INSTALLATION Workmanship and roof failures are discussed atWORKMANSHIP & ROOF DAMAGE and at LADDERING & STAIR STEPPING SHINGLES
Underlayment Effects on Shingle Life: omitting the roofing underlayment (roofing felt or "tar paper" installed over the roof deck before shingles are applied), installing underlayment or shingles over a wet, icy, or snow-covered roof deck Roofing underlayment details are atUNDERLAYMENT REQUIREMENTS on ROOFS
Roof Flashing Errors: there are too many of these to list on this asphalt shingle page. Water runs down hill. Flashing installers
sometimes forget that, misplacing flashing, omitting flashing, using continuous rather than step flashing at roof-wall abutments and
at chimneys, improper valley flashing, nails through flashing, relying on roof cement rather than flashing, and misplacement of drip
edge with its vertical section behind rather than over gutters. OPINION: some roofers opine that underlayment is completely unnecessary.
I go with the manufacturer's recommendations. They have a high interest in the successful application of their product.
See these roof flashing articles: FLASHING, ASPHALT SHINGLE VALLEYS FLASHING MEMBRANES PEEL & STICK FLASHING for METAL ROOFS FLASHING ROOF WALL DETAILS FLASHING ROOF-WALL SNAFU FLASHING SIDING DETAILS FLASHING WALL DETAILS FLASHING WOOD ROOF DETAILS
Effects of Climate On Asphalt Shingles: Carl Cash asserts that the mean durability of
"20-year" shingles is less than 20 years everywhere in the U.S. except Alaska. Variations in climate
permit calculation of a wear-acceleration factor for various cities. Higher
thermal load (hotter climates) means shorter life. Yuma, AZ mean durability
was calculated at 12.6 years, for example, and Ft. Meyer FL 14.1 years while
Chicago at 19.7 years and Erie, PA at 20.7 years showed longer life in cooler
climates.
Cost Effectiveness of Asphalt Shingles:
Other roofing materials also are affected by thermal loading. Cash calculates that the life cycle cost of
steep-slope roofing shows that asphalt shingles still provide the most economical performance for the home owner! ("Asphalt Shingle Performance," --
Carl Cash.)
Given these variables, it is not likely that a "20-year" shingle will
expire exactly twenty years after it is installed. When a roof lasts longer
than its promised life no one complains. If a roof needs replacement
substantially sooner than its anticipated life, consumers are understandably
concerned.
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
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.
Carl Cash, P.E., Construction Business and Technology Conference, Providence
Rhode Island, 2/28/97
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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