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.

    

Variations among Asphalt Composition Shingles

  

Shingles that look similar can vary widely in quality. Although some standards exist, in the past, compliance has been voluntary.  As an inspector, you will not be able to tell whether shingles comply with any standards simply by looking at them.

  

The table below, compiled from information based on laboratory testing performed by Jim D. Koontz and Associates which used ASTM standards for testing criteria, illustrates the degree to which the quality and strength of different asphalt shingles vary.

  The table includes test results for fiberglass shingles made by 13 different manufacturers. Six 3-tab shingles and seven laminated shingles were tested in order to compare their performance characteristics.

  

Shingle (example/type)	Tear Strength (grams)	Tensile Strength (lbs/ft)	Mat Weight (lbs/100ft2)	Pull-Through, Single Layer (lbs/ft)	Pull-Through, Laminate Area (lbs/ft)	Pull-Through, Nailable Area (lbs/ft)
#1  3-tab	1,240	109	2	24.34	--	40.48
#2  3-tab	2,190 H	119 H	2.15	32.25 H	--	58.23 H
#3  3-tab	1,640	112	2.1	28.35	--	46.31
#4  3-tab	1,720	112	2.17 H	27.89	--	46.05
#5  3-tab	930 L	82 L	1.67	19.5 L	--	38.55
#6  3-tab	1,790	103	1.8	22.74	--	33.4 L
H/L Difference	135%	45%	29%	65%	--	75%
					Average	70%
#1  laminate	1,570	121 H	2.15 H	22.77	48.18	85.37
#2  laminate	1,840 H	109	2.12	29.91 H	50.89 H	104.6 H
#3  laminate	1,180	111	2.03	16.46 L	44.75	80.83
#4  laminate	830 L	82 L	1.8	16.65	24.55 L	54.63 L
#5  laminate	1,030	89	1.9	29.22	32.43	67.53
#6  laminate	1,750	93	2.04	25.49	44.89	87.43
#7  laminate	1,470	118	2.08	25.51	43.32	81.81
H/L Difference	121%	47%	19%	81%	107%	91%
					Average	78%

 

The ASTM standard for minimum tear strength is 1,700 grams (ref. D1922).  This figure applies to the first column, labeled "Tear Strength."

 

The numbers in red show test results for shingles that failed to comply with the ASTM minimum requirement.  The 3-tab shingle #1 failed to comply in the tear-strength test because it tore at only 1,240 grams.

  

Additional ASTM requirements relevant to this table include:

 

• 1.35 for "Mat Weight" (ref. D3462); and
• 20 for "Pull-Through, Single Layer."

 

The row labeled "H/L Difference" shows the percentage of difference between high and low results for each type of test.  In the "Tear Strength" column, there is a 135% difference between the highest result (#2, 3-tab shingle) and the lowest result (#5, 3-tab shingle).

 

As you can see the general performance characteristics of 3-tab shingles varied by an average of 70%. The performance characteristics of laminated shingles vary by an average of almost 80%.

 

In the tear strength test, 60% of the shingles tested were sub-standard, and the difference between high and low averaged 130%.

 

The purpose of the single and double pull-through tests is to simulate proper and improper nailing. If shingle fasteners are placed too high on the shingle, they’ll penetrate only one layer instead of two.

 

What all this really means is that identical conditions or forces might damage one brand of shingle but not another similar shingle.  With such a wide variation in shingle quality, it’s difficult to make generic statements that are true for all shingles.