Mastering Roof Inspections: Asphalt Composition Shingles, Part 1
Asphalt Composition Shingles
This and some of the following articles in the series “Mastering Roofing Inspections” will help you recognize and identify defects and damage in asphalt composition shingles, as well as determine the sources of those problems as often as possible and make good recommendations.
This covers the standards and best practices related to the fabrication and installation of shingles, including the different types of shingles and their performance characteristics, and their related components such as underlayment, flashing, and fasteners.
It also covers general industry accepted installation methods, where to look for defects, how to recognize them, how to determine how severe they are, and how to tell when shingles are at or near the end of their useful life. With a forensic approach to inspecting asphalt shingles, you will learn to compare what you see with what you know. Once you’ve learned the basics, you can identify all kinds of problems.
Although we use common terminology, sometimes different names are used for the same things in different parts of North America. The terms you choose are not as important as making sure you explain the terms clearly and understandably.
Asphalt Shingles Components
The terms “asphalt” tile and “composition” tile are general terms for the same. The term “composition” is used because shingles are a composite product made from a fiberglass or cellulose mat and asphalt and minerals, as opposed to a single material, such as wooden shingles or clay tiles.
All modern shingles made in North America have mats made of interwoven fiberglass strands, so you may also hear them called “fiberglass” shingles. A modern shingle consists of a fiberglass mat embedded in asphalt and covered with granules on the weather-facing surface. The mat, asphalt and granules work together to form a durable, flexible and waterproof package.
In the past, shingles were also made using mats made from cellulose-based materials, and these are called “organic” shingles.
The mat provides the reinforcement that gives the shingles the strength to help resist breaking, tearing and pulling from fastener heads.
Although the mat is less than 2% of the weight of the tile, a small difference in the thickness of the mat can make a big difference in the tear strength of the tile.
This unsaturated fiberglass mat will give you a better idea of what one looks like before it is saturated with asphalt.
More Resistant to Heat and Humidity
Fiberglass shingles are more resistant to heat and humidity than organic shingles. Warm air can hold more moisture than cold air. Because they absorb less moisture, fiberglass shingles deform less as they age, making them more stable in hot or humid climates.
Also, because fiberglass mat does not absorb moisture, as fiberglass shingles age and lose volatiles, they deform less than cellulose shingles. “Volatiles” are compounds in asphalt that help keep shingles waterproof, flexible, and durable, but they dissipate over time. Most of the volatiles dissipation is due to evaporation due to overheating.
Variations in Performance
The downside to fiberglass shingles is that there are wide variations in performance between similar shingles made by different manufacturers.