February 26, 2017
Guide to Understanding Roof Shingles – Part 1: Composite Asphalt Shingles
When performing our 15-point inspection and roofing process, many customers ask “What are asphalt shingles made of?” and “Will they really last for fifty years?”
These questions are fundamental, as knowledge of your shingles’ composition will help you take better care of your roof – which is one of the most important components of your home.
Asphalt shingles are sometimes called composite shingles because they are composed of different layers. Each layer serves a particular function:
- Base Mat
A shingle’s middle layer is called the “base mat”, which is the backbone of a shingle. The base mat holds the shingle together and it is used to resist tearing during handling and installation. Older shingles were made with an organic-base mat, and while major Canadian and US manufacturers no longer produce the organic-base mat, it is still found on many roofs today. Examples of organic-base asphalt shingles can be found on roofs that were built as early as 20 years ago.
Today, most manufacturers produce fiberglass-base shingles. These shingles have a Class A fire resistance rating and will last between 18 to 50 years, depending on the type of installation, the weight of the shingle, shingle quality, and weather condition. In comparison, the organic-base shingle will last between 15 to 25 years.
The base mat is saturated with waterproofing asphalt and then the surface is covered with mineral granules. Generally, fiberglass-base shingles contain more asphalt as the mat is thinner than the mat used in organic-based shingles. The more asphalt used, the heavier and more durable the shingle becomes.
Shingle granules are made from crushed natural stones. Besides providing an aesthetic appearance for the shingle, the granules protect and preserve asphalt shingles from solar ultraviolet radiation. It is common that some granules will come off the shingles when the roof is installed; this loss of granules is normal as long as the asphalt is not exposed.
The quality of the asphalt plays a crucial part in the longevity of the shingles. In order to produce greater results, manufacturers have developed and use modified asphalt to strengthen roof shingles. There are two basic types of modified asphalt shingles:
- SBS (styrene-butadiene-styrene) modified shingles
- APP (atactic polypropylene) modified shingles
The most popular type of asphalt shingles used on slopped residential roofs is the SBS modified asphalt shingles. SBS modified shingles are elastic and rubberized while APP modified shingles are plastic and rigid. The flexible nature of the SBS modified shingles make this the ideal shingle for climates with cold winters and hot summers.
With a greater understanding of the roofing system, homeowners can make informed decisions to best maintain and retain the value of their home.
Safe Roof. Happy Families.