Shingle Damage Evaluation – Composite Asphalt Shingles – Part 2

Posted by in Shingles | May 04, 2012

This post is Part 2 of Shingle Damage Evaluation and follows the Introduction.

Composite Asphalt Shingles

The use of asphalt shingles began in the early 20th Century with the cutting of roll roofing into smaller pieces to mimic shakes or slate.  Asphalt shingles have been basically comprised of a mat encased in asphalt and a topside covered with ceramic granules.  The mat provides the base or structure of the shingle.  It is coated with asphalt to provide water shedding ability and covered with granules on the topside to reduce damage from foot traffic and degradation of the asphalt by the sunlight.  See Figure SDE-1.


Figure SDE-1 A typical three-tab shingle.


The basic construction of a shingle has varied little over the past century due to advances in the materials.  There are now also different types of shingles that offer a variation in appearance, durability, strength, wind resistance, etc.  The asphalt shingles commonly found on roofs today have an organic mat or a fiberglass mat.

The mat of an organic shingle is comprised of a cellulose fiber made from wood, recycled rags, and/or recycled paper. For those of us who remember the good old days of kindergarten, an organic mat looks and feels similar to the thick construction paper that we used for our art projects, except it is thicker and stronger.  The organic mat is first saturated with asphalt.  The asphalt provides some strength and flexibility, and promotes water shedding on a pitched roof.  The granules on an organic mat are bonded to the asphalt encased mat with a second layer of asphalt coating (the flaking of the second coat may be seen in Figure SDE-2).  Shingles with an organic shingle mat were the most popular prior to 1980.


Figure SDE-2 Flaking of granules and bond coat exposes asphalt mat below.


Since about 1980, fiberglass shingles have become more common.  The mat of these is comprised of a fiberglass weave. The fiberglass mat is soaked with one coating of asphalt and covered immediately with granules.   Since asphalt does not bond well to fiberglass, the fiberglass mat must be coated with a bonding agent prior to being soaked with asphalt.  Since there is only one coating of asphalt during fabrication, a fiberglass mat shingle is usually thinner and lighter than an equivalent organic mat shingle.


Figure SDE-2 Fiberglass mat. Note fibers encased in asphalt.


The most commonly used shingle is the three-tab shingle (Figure SDE-1).  There are also shingles with a laminate or an appliqué to produce a thicker or decorative appearance.  A laminate shingle is comprised of two narrow strips of shingle that are bonded together, see Figures SDE-3 & 4.  This construction gives a more three‐dimensional appearance to the shingle.


Figure SDE-3 Laminate shingle construction shown in a sketch.


Figure SDE-4 Laminate shingle.


A three‐dimensional appearance may also be accomplished by adding a second coating of asphalt and granules, commonly called an appliqué, over a portion of the shingle already covered with asphalt and granules. This is similar to the application of an appliqué on a T‐shirt. The appliqué method results in a greater thickness of asphalt over some portions of the shingle (Figure SDE-5). And like the appliqué on a cheaper T-shirt, it often degrades easily, cracks, and peels.


Figure SDE-5 Appliqué shingle in service. Note that a second layer of asphalt was added for a raised layer of granules.


When composite asphalt shingles are new they are relatively soft and flexible.  The soft and flexible shingles are usually able to accommodate the thermal movement during temperature changes, both from within and from adjacent components, and vertical or horizontal roof movements during snow and wind loading.  They are also more resist to damage from impact by hard objects, such as hail stones.  As asphalt shingles age, they lose softness and flexibility.  The loss of softness and flexibility reduces their ability to accommodate thermal movements and impacts.

For more information about shingle manufacturing, visit the GAF website or watch the GAF shingle manufacturing process video or visit the website of another shingle manufacturer.  Our referencing of GAF is not necessarily an endorsement of them or their products, recommendations, opinions (especially with regard to their technical bulletin regarding hail damage), corporate stand on any issues, etc., but we thank them for providing technical information helpful for learning about the manufacture and installation of their products.

The next topic will be the Effects of Aging on Composite Asphalt Shingles.