Mastering Roof Inspections: Asphalt Composition Shingles, Part 8

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/100 ft2)

Pull-Through, Single Layer (lbs/ft)

Pull-Through, Laminate Area (lbs/ft)

Pull-Through, Nailable Area (lbs/ft)

ASTM Requirement

D1922:
1,700

 

D3462:
1.35

20

 

 

#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 standards for minimum tear strength is 1,700 grams (ref. D1922).  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.

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 varied 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.

 

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Learn how to master a roof inspection from beginning to end by reading the entire InterNACHI series: Mastering Roof Inspections.

 

 InspectorSeek.com


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