Mastering Roof Inspections: Asphalt Composition Shingles, Part 7

 

by Kenton Shepard and Nick Gromicko

    

The purpose of the series “Mastering Roof Inspections” is to teach home inspectors, as well as insurance and roofing professionals, how to recognize proper and improper conditions while inspecting steep-slope, residential roofs. This series covers roof framing, roofing materials, the attic, and the conditions that affect the roofing materials and components, including wind and hail.

  

PERFORMANCE STANDARDS

  

Asphalt shingles are designed with different performance characteristics, such as resistance to damage from fire, impact and wind. Standards are available that specify minimum performance levels and material properties.

 

The standards with which shingles have to comply are determined by the authority having jurisdiction (AHJ) in the area where the home is built. The AHJ is often the local building department. A city, county, state or province may also be the AHJ.

 

Most of these standards have been developed by one of the following three organizations.

 

ASTM International

  

ASTM International is a major developer of standards, including standards for asphalt shingles.  However, they don’t test or certify shingles.

  

Underwriters Laboratories

 

The Underwriters Laboratories (UL) specializes in performing testing and certification of various products.  They test shingles to determine whether a particular type actually meets a particular standard. If that shingle product completes the testing successfully, the UL will issue a certification which lists any standards with which that shingle complies.

 

Canadian Standards Association

 

In Canada, the Canadian Standards Association (CSA) develops standards for asphalt shingles, and provides testing and certification.

 

TESTING SHINGLES

 

Some of the more common standards developed by the ASTM are for shingle tear strength, and resistance to fire, impact and nail pull-through.

 

Fire- and impact-testing protocols are the same for all types of roof-covering materials. Asphalt and wood shingles, shakes and tiles all undergo the same testing procedures.

 

Tear Strength

 

Tear strength is a measurement of how easily a shingle is torn. Tear strength is especially important because testing has shown that this property has a greater correlation to shingle toughness and resistance to cracking than any other factor, including tensile strength. The standard test for tear strength is called the Elmendorf Test.

 

Pull-Through Resistance

 

Nail pull-through resistance is the measurement of the number of pounds required to pull a shingle over the head of a roofing nail at a specific temperature.

 

RATING SHINGLES

 

Through standardized testing, shingles can be rated for resistance to various types of environmental damage.

 

Fire Resistance

 

Fire-resistance testing is performed for compliance with ASTM standards.  Although these tests are considered performance tests and are conducted regularly on new shingles, no correlation has been established between performance in these tests and performance in actual fires. The tests are more for purposes of comparison.

 

There are three fire ratings for roof-covering materials:  A, B and C.  Class A is the highest rating, and nearly all asphalt shingles are rated Class A.

 

Impact Rating

 

The Underwriters Laboratories provide standards for impact resistance. Hail damage falls into this category. Shingles are impact-rated Classes 1 through 4, with Class 4 shingles being the most resistant to damage from impact.

 

Other Testing

 

Individual manufacturers may also have in-house testing for factors such as uplift flexibility. This test measures the residual strength of an unsealed shingle tab after it has been bent to 90 degrees.

 

As a home inspector, you’re not required to confirm shingle compliance with standards, and, without documentation, you won’t be able to.  Confirming compliance exceeds InterNACHI's Standards of Practice, but having some basic knowledge about existing standards will help build your library of knowledge and improve your understanding of asphalt shingles, which will, in turn, improve your judgment in evaluating the conditions you find on a roof.