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Chapter 10.  Shingles and Shakes

Definitions and Measurements

      Exposure and Coverage

      Square and Bundle

      Weight

      Estimating Cubic Volume Equivalents

            •Method 1.  From area coverage

            •Method 2.  From running inches

Manufacturing and Recovery

      Bundles per Log  

      Squares per Log  

Log Volume Requirement


Chapter 10.  Shingles and Shakes

        In the past, western redcedar was the species most commonly used for shingles and shakes, but advances in wood preservation and fire retardant treatments have increased the use of species such as hemlock and true fir. Either shingles or shakes may be used for roofing or siding, with the choice depending on the appearance preferred by the consumer. Shingles are sawn on both surfaces and therefore present a rather smooth and precise appearance. They are manufactured in 16, 18, and 24 inch lengths and three grades. Width is gen­erally random, but fixed widths can be obtained. They taper in thickness, and the convention is to measure the thickest (butt) end. Thickness may be reported in terms of the butt thickness or as the number of butts that stack to a given thickness. Thus a 4/2 thickness designation means that 4 butts measure 2 inches thick. Table 10-1 presents data for common shingle grades and sizes. Shakes or handsplit shakes are split on at least one surface and have a more rugged, irregular texture than shingles. They are made in 18 and 24 inch lengths. Table 10-2 contains data for common shake products.

Definitions and Measurements

Exposure and Coverage

        Exposure refers to the distance between the butt end of a shingle in one course, or layer, and the butt end of a shingle in the next overlapping course. Coverage refers to the area of roof or wall that is covered at the recommended exposure.

Square and Bundle

        A square is a quantity of shingles that yields 100 square feet of coverage. A bundle is a pack in which shingles are laid in alternate directions with the butts to the outside and bound in the middle where the tapered ends overlap. Bundles are referred to by the number of courses of butts at each end; a 20/20 bundle has 20 layers at each end, or 40 layers in total. Bundles are usually packed so that four bundles of shingles or five bundles of shakes constitute a square. Tables 10-1 and 10-2 indicate coverages per bundle for various sizes and exposures of these products. Estimating the number of bundles required for a job is done by measuring the area to be covered and dividing by the coverage per square for the recommended exposure.Running inches refers to the lineal distance that the shingles will cover when placed side by side. These values are averages from actual installations.

Weight

        Tables 10-1 and 10-2 show average weights of squares. The weight of a bundle is one-fourth (shingle) or one-fifth (shake) the weight of a square.

Estimating Cubic Volume Equivalents

        The cubic volume of a square can be estimated in two ways:  from area coverage or from running inches. The volume of a bundle is either one-fourth (shingle) or one-fifth (shake) the volume of a square.

Method 1.  From Area Coverage
. The 100 square foot coverage of a square represents 14,400 square inches. Running inches can be estimated by dividing by the exposure (E). Multiplication by shingle length (L) and the average thickness (T) yields the cubic volume:

        V, ft3  =  (L * T * 14,400) / (E * 1,728).

The value 1,728 converts cubic inches to cubic feet. See Example 1.

Method 2.  From Running Inches.     A similar calculation uses the running inches (R) from Table 10-1:

        V, ft=  (L * T * R) / 1,728.

 

Example  1          

Calculate the cubic foot volume of a square of 16 inch shingles having a thickness of 0.4 inch when the exposure is 5 inches. In this case, it is assumed that the thickness at the small end is 1/15 (0.0666) inch.

        {16 * [(0.4 + 0.0666) / 2]  *  14,400}  /  (5 * 1,728)  =  6.22 ft3.

A bundle of these shingles would contain 1.56 ft3.

Example  2          

How many bundles of shingles in Example 1 can be ob­tained from a cubic foot of log? Table 10-3 indicates that 24% of incoming log raw material will be recovered as shingles.

        (1 ft3log * 0.24 ft3shingle/ft3log) / (1.56 ft3shingle/bundle)  =  0.154 bundle/ft3log.

The recovery study obtained 337 bundles of shingles from 2,119 ft3 of logs, giving a ratio of 0.159 bundle percubic foot of log. Similarly, the recovery study obtained 0.293 bundle of shakes per cubic foot of logs.

Example  3

Using Example 2, calculate the cubic feet of log needed to produce

one bundle of shingles  1/0.159  =  6.29 ft3 log per bundle

one square of shingles  1/0.040  =  25.0 ft3 log per square

one bundle of shakes    1/0.293  =  3.41 ft3 log per bundle

one square of shakes    1/0.059  =  17.0 ft3 log per square

                                                                                                       

Manufacturing and Recovery

        The process of shingle and shake manufacture involves two basic steps: cutting fixed length bolts of suitable quality from logs and then sawing or splitting shingles or shakes from the bolts. Table 10-3 shows results of a shingle and shake recovery study using western redcedar. The data portray both the recovery of bolts from log raw material and the recovery of shingles or shakes from the bolts. The shingle study was based on 31 pieces (logs, chunks, and slabs) that had an average net volume of 68 cubic feet. Of this, 72% was recovered as bolts. When processed, 33% of the bolt volume (24% of the original raw material) was recovered as shingles. The shake study was based on 61 pieces that had an average net volume of 66 cubic feet. About 87% of the raw material was recovered as bolts. When processed, 60% of the bolt volume (53% of the original raw material) was recovered as shakes. About 43% of the shakes were graded as heavy, 45% as light, and 12% as other grades.

Bundles per Log

        To calculate bundles per cubic foot of log, multiply the log volume in cubic feet by the cubic recovery percent in decimal form and divide the result by the cubic foot volume of a bundle of the appropriate product. See Example 2.To calculate bundles per cunit (100 ft3) of log, multiply the result of Example 2 by 100.To obtain bundles per cubic meter of log, multiply the result of Example 2 by 35.315 ft3/m3 or substitute metric equivalents of each item in Example 2.

Squares per Log

        Divide the result obtained above for bundles by  four bundles per square for shingles or five bundles per square for shakes:

        Squares of shingles per ft3 of log  =  0.159 / 4  =  0.040.

        Squares of shakes per ft3 of log  =  0.293 / 5  =  0.059.

Log Volume Requirement

        To calculate the volume of log required per bundle or square, take the reciprocal of the result obtained above. See Example 3.


Table 10-3.  Material balances for shingles and shakes.

 

Shingles

Shakes

 



Quantity

% of raw
material
volume


% of bolt
volume



Quantity

% of raw
material
volume


% of bolt volume

 

Wood raw material
(logs, chunks, slabs)


31 pieces

   


61 pieces

     

Net volume

2,119 ft3

   

4,020 ft3

     

Average volume

68 ft3

   

66 ft3

     

Bolt recovery

             

Bolt volume

1,520 ft3

72

 

3,505 ft3

87

   

Residue

599 ft3

28

 

515 ft3

13

   

Total

2,119 ft3

100

 

4,020 ft3

100

   

Shingle/shake recovery
from bolts

             

Product

505 ft3

24

33

2,118 ft3

53

60

 

Residue

1,015 ft3

48

67

1,387 ft3

34

40

 

Total

1,520 ft3

72

100

3,505 ft3

87

100

 

Number of bundles

337a

   

1,185b

     

Number of squares

84-1/4

   

237

     
     

Grade distribution of shakes

 
     

Grade

ft3

%

Bundles

 
       

Heavy

910

43

454

 
       

Light

950

45

586

 
       

Other

258

12

145

 
       

Total

2,118

100

1,185

 

Source: USDA Forest Service, Pacific Northwest Research Station (unpublished).

aAt four bundles per square.

bAt five bundles per square.

 

 
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Last Updated 2/2/2012 5:37:22 PM