•Method
1. From area coverage
•Method
2. From running inches
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 101 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 102 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 101
and 102 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 101 and 102
show average weights of squares. The weight of a bundle is onefourth
(shingle) or onefifth (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 onefourth (shingle) or onefifth (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, ft^{3} = (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 101:
V, ft^{3 }= (L _{* }T _{*} R)
/ 1,728.
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 ft^{3}.
A
bundle of these shingles would contain 1.56 ft^{3}.
How many bundles of shingles in
Example 1 can be obtained from a cubic foot of log? Table 103
indicates that
24% of incoming log raw material will be recovered as shingles.
(1 ft^{3}log_{
* }0.24 ft^{3}shingle/ft^{3}log)
/ (1.56
ft^{3}shingle/bundle) = 0.154 bundle/ft^{3}log.
The recovery study
obtained 337 bundles of shingles from 2,119 ft^{3}
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.
Using Example 2, calculate the cubic
feet of log needed to produce
one
bundle of shingles 1/0.159 = 6.29 ft^{3}
log per bundle
one
square of shingles 1/0.040 = 25.0 ft^{3}
log per square
one
bundle of shakes 1/0.293 = 3.41 ft^{3}
log per bundle
one
square of shakes 1/0.059 = 17.0 ft^{3}
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
103 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 ft^{3}) 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 ft^{3}/m^{3} 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 ft^{3} of log = 0.159
/ 4 = 0.040.
Squares of shakes per ft^{3}
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
103. Material balances for shingles and
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 ft^{3}



4,020 ft^{3}




Average volume

68 ft^{3}



66 ft^{3}




Bolt recovery








Bolt volume

1,520 ft^{3}

72


3,505 ft^{3}

87



Residue

599 ft^{3}

28


515 ft^{3}

13



Total

2,119 ft^{3}

100


4,020 ft^{3}

100



Shingle/shake recovery
from bolts








Product

505 ft^{3}

24

33

2,118 ft^{3}

53

60


Residue

1,015 ft^{3}

48

67

1,387 ft^{3}

34

40


Total

1,520 ft^{3}

72

100

3,505 ft^{3}

87

100


Number of bundles

337^{a}



1,185^{b}




Number of
squares

841/4



237







Grade distribution of shakes





Grade

ft^{3}

%

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).
^{a}At four bundles per square.
^{b}At five bundles per square.
