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This roof leak article explains the causes & effects of loss of protective mineral granules from roof shingles.
Shingle granule loss defects occur on organic-mat or fiberglass-mat
asphalt roof shingles and, depending on the cause and extent of mineral granule loss, the loosening
of this protective coating can spell the end of life of an asphalt shingle roof or the demise of a mineral-granule-coated roll roofing roof.
Roof shingle granule loss may be normal shingle wear, hail damage wear, or defective roofing product, as we explain here. The page-top photograph shows severe loss of mineral granules from an asphalt shingle roof. This "bald" asphalt shingle 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.
Readers are also invited contribute roof failure information to the web author for research purposes.
web author for research purposes.
The job of these mineral granules which are adhered to the roof shingle surface as part of the shingle manufacturing process, is to protect the
shingle from sunlight, from UV light, and from the weather in general.
The selection of roof shingle color is also determined
by the choice of its coating of mineral granule; lighter colored shingles may remain a bit cooler and at least in some applications
(hot sunny climates) may have a longer life than dark-colored shingles.
Types of Mineral Granule Loss on Asphalt Roofing Shingles
While in our page top photo the roof is "worn out",
there are quite a few other conditions that can produce mineral loss on asphalt shingle roofs. Diagnosing the correct cause of granule loss is useful in helping to assess the probable remaining roof life and it may play a role in roof shingle warranty claims or insurance claims related to storm or hail damage.
Below we define, contrast, and illustrate all types of mineral granule losses that occur on asphalt roofing:
Mineral granule loss on a new asphalt shingle roof
Mineral granule loss on an asphalt shingle roof due to normal aging
Mineral granule loss due to roof shingle blistering
Mineral granule loss on old, worn-out asphalt shingle roofs
Mineral granule loss from being walked-on or mechanical damage
Mineral granule loss due to hail or other storms
Mineral granule loss due to defective roofing product
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. You can begin this roof condition assessment at the ground, before even looking at the roof itself.
If the roof is reported to be new, the granules shown in our photo are normal and not a worry. [Or they could be there having washed off of an older worn out roof that was just replaced.] Especially right after an asphalt roof has been installed, granules that were loosened on it surface from walking by the installers will wash down and off of the roof surface. Provided the roofers were careful not to dance the Twist while roofing on a hot day, the roof should be fine.
But if the granules appear after a hail storm, or if the roof is quite old, they are more likely to indicate roof wear and/or damage.
Just take a close look at the shingles themselves for granule loss. And if you clean out the gutters you'll find it easy to see if this granule loss is continuing. Look in the roof gutters for shingle granules too.
Roof granule loss due to normal aging occurs over the life of an asphalt shingle roof as weather and sun exposure cause the roof shingle to lose its flexibility, as the roof is exposed to changing temperatures, etc.
Normal shingle granule loss means that there has been no single event that has damaged the roof, that the quantity of granules lost from or remaining on the shingles is typical for the chronological age of the roof, and that thus the "wear age" of the roof (it's remaining life compared with its original warranty or projected roof life) is about the same as the roof's chronological age, after we factor in ASPHALT SHINGLE LIFE / WEAR FACTORS.
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,
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.
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 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.
The (older, more brittle) roof at left suffered both granule loss and cracked shingle corners after it was walked-on.
This is damage
caused by workers and is not a product defect. Some examples and photos of shingle damage that occurred at least in part due to foot traffic on a roof, and that produced lots of granule loss from the surface can be seen at MECHANICAL DAMAGE of SHINGLES.
At an arbitration hearing involving a roof dispute we could actually track the footprints (and damage) across an older roof that had been walked-on (and damaged) by the very contractor who told the owner she needed a new roof. (Don't walk on fragile roof surfaces).
Granule loss on asphalt shingles due to storms, especially hail: 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.
See HAIL DAMAGED SHINGLES for more detail on this source of asphalt shingle roof
damage and for more photographs of asphalt shingles that have been deprived of their protective coating of mineral granules.
Roof shingle granule loss due to defective roofing product usually exposes the shingle substrate in "premature bald" patches and is identified by bald spots or exposed shingle substrate on roofs early in their chronological life, often distributed uniformly over the roof or in areas of the roof where shingles from a particular pallet of roof shingles were installed.
Our photo (left) of granule loss on an asphalt shingle roof was provided by ASHI Home inspector Steve Mauer.
The organic felt-based asphalt shingles shown at below left has lost some granules into the roof gutter but an inspection of the shingles themselves showed no significant bald areas. We had to look closely at those shingles in the upper right of the photo and we decided the wear was probably due to foot traffic as well.
The organic-mat asphalt roof shingle shown at right, also showing normal wear, is completely worn out, showing shingle substrate, sun and heat damage, and basically, that the roof needs to be replaced. A shingle like the one shown is usually so fragile that stepping on it breaks it into many small fragments.
These shingles (above right) may already be leaking into the roof substrate, placing water
between the shingle and its felt underlayment, between the underlayment and the roof sheathing, or leaks may be
entering the roof structure. Even if there is no visible evidence of leaks in the living area (such as stains on
top floor ceilings or visible water in the attic) this roof is at the end of its life.
Wherever and whenever a roof shingle has lost the protection of its mineral granules that
shingle has a reduced life expectancy. In all climates the loss of granules 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.
Mineral Granule Loss Due to Defective Roofing Product
Below (left), the picture of bald areas in this laminated asphalt shingle or "architectural shingle" roof show white fiberglass roof shingle substrate. Our OPINION was that this was a defective roof product. This same roof also suffered thermal splitting or tearing damage (below right). Photos of roof damage below were provided by ASHI Home inspector Steve Mauer and photographed in 2009.
Our OPINION is that the asphalt roof shingle granule loss shown at below left is due to a defective product.
How to Inspect a Roof for Loss of its Protective Coating of Mineral Granules
Check the shingle surface for mineral granule loss
The critical place to evaluate the condition of roof shingles is at the edge of or (if safe and the roof is not fragile), on
the roof itself. Look closely at those shingles - get down on your hands and knees and look closely for early wear signs such as
tiny bald spots, pits, cracks, or other damage. If you can't see obvious bald areas from which the protective granules have been lost
from the shingle, it's unlikely that granule loss is a current problem.
Look in the gutters for lost mineral granules from the roof
The photograph at above left shows a modest amount of mineral granule wash-off into the gutter of this home.
If the roof is a new one, this may be a normal amount of granule loss. When the gutter is cleaned out completely, you should
not see this same level of mineral granules again soon. If you do, there may be a rapid wear problem going on with the roof, or
someone may be dancing on it.
The photograph at above right shows a significant loss of mineral granules into the gutter on this roof. A look at the
scoured surface of the roof shingles and a report by the owner of a recent and significant hail storm suggest that this granule
loss may have been due to hail damage. we discuss evaluating hail damage to roofs and how to distinguish hail damage from
other sources of shingle granule loss at HAIL DAMAGED SHINGLES.
Look on the ground for lost mineral granules from the roof
Check the ground surface at the end of the downspouts or roof leaders. If you see lots of mineral granules there the roof
is either brand new or badly worn. A check of the roof surface easily distinguishes between these two conditions.
Translating Asphalt Shingle Damage or Wear into the Decision to Re-Roof
Extensive shingle granule loss alone, sufficient to expose the roof shingle substrate, means that the wear rate on the roof will accelerate. That's because the shingle body is exposed to direct sun and in freezing climates because the exposed shingle substrate begins to absorb water, suffering from the freeze-thaw cycle. In other words, once the shingle substrate is exposed by mineral granule loss, that area of the shingle will absorb
more water than its neighbors.
When shingle granule loss is extensive or when it is combined with other roof defects (such as tears, cracks, brittle shingles that can't be walked-on for patching, or more than just a very few readily-accessible (patchable) defects, those will usually form a sound basis for asserting that the roof is already leaking (at those cracks) even if water has not appeared on finished ceilings inside the home, and they both argue that this roof has no predictable useful remaining life.
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The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, 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. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
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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).