jii Bureau of Standards
The program of research on building materials and structures, carried on by the

National Bureau of Standards, was undertaken with the assistance of the Central Housing Committee, an informal organization of governmental agencies concerned with

housing construction and finance, which is cooperating in the investigations through a committee of principal technicians.

CENTRAL HOUSING COMMITTEE

ON RESEARCH, DESIGN, AND CONSTRUCTION

A. C. Shire, Chairman.

United States Housing Authority.

Howard P. Vermilya, Vice Chairman.

Federal Housing Administration,

Sterling R. March, Secretary.

'Pierre Blouke,

Federal Home Loan Bank Board.

Hugh L. Dryden,

National Bureau of Standards.

Louis A. Simon,

Public Buildings Administration.

Luther M. Leisenring,

Construction Division (War).

Edward A. Poynton,

Office of Indian Affairs.

John S. Donovan,

Farm Security Administration.

George W. Trayer,

Forest Service (F. P. Laboratory).

Joseph M. DallaValle,

Public Health Service.

George E. Knox,

Yards and Docks (Navy).

William R. Talbott,

Veterans' Administration.

Wallace Ashby,

Bureau of Agricultural Chemistry and Engineering.

NATIONAL BUREAU OF STANDARDS

STAFF COMMITTEE ON ADMINISTRATION AND COORDINATION

Hugh L. Dryden, Chairman,

Mechanics and Sound.

Phaon H. Bates, Gustav E. F. Lundell,

Clay and Silicate Products. Chemistry.

Hobart C. Dickinson, Addams S. McAllister,

Heat and Power. Codes and Specifications.

Warren E. Emley, Henry S. Rawdon,

Organic and Fibrous Materials. Metallurgy.

The Forest Products Laboratory of the Forest Service is cooperating with both

committees on investigations of wood constructions.

[For list of BMS publications and directions for purchasing, see cover page iii]
UNITED STATES DEPARTMENT OF COMMERCE • Jesse H. Jones, Secretary

NATIONAL BUREAU OF STANDARDS • Lyman J. Briggs, Director

BUILDING MATERIALS

and STRUCTURES

REPORT BMS70

Asphalt-Prepared Roll Roofings and Shingles

by

HUBERT R. SNOKE

ISSUED APRIL 10, 1941

The National Bureau of Standards is a fact-finding organization;

it does not "approve" any particular material or method of construction. The technical findings in this series of reports are to be construed accordingly.

UNITED STATES GOVERNMENT PRINTING OFFICE • WASHINGTON • I94I

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, WASHINGTON, D. C. • PRICE I5 CENTS
Foreword

This report is the second of a series deahng with the properties and appUcations of roofing materials suitable for use in low-cost house construction. The first, Metallic

Roofing for Low-Cost House Construction, has been published as Building Materials

and Structures Report BMS49, copies of which may be obtained as described on cover page III. Asphalt-prepared roofings, the subject of the present report, while comparative newcomers in the field of roofing, are widely used today. Available literature on this subject is mainly of a teclmical or an advertising nature. The purpose of this report is to furnish information that will be of value not only to architects, engineers, specification

writers, and roofing contractors but also to the average home owner.

Lyman J. Briggs, Director.

[n]
Asphalt-Prepared Roll Roofings and Shingles

BY Hubert R. Snoke

CONTENTS

Page

Foreword ii

I. Introduction 1

1 . Historical 1

2. General 2

II. Definition of asplialt-prepared roofing 3

III. Materials used in asphalt-prepared roof- ings 3

1. Felt 3

2. Asphalt 4

3. Surfacing materials 4

4. Composition of typical roofings 5 IV. Manufacture of asphalt-prepared roofings. 6 V. Factors which should be considered in purchasing asphalt-prepared roofings- 7

1. Roll roofings 7

2. Asphalt shingles 8

(a) General discussion _^ 8

(b) Coverage 9

(c) Headlap 11

(d) Sidelap 11

(e) Exposure 11

(f) Weight 12

(1) Per unit area of shingle 12

(2) Per unit area of roof _ _ 12

(g) Cost 14

VI. Methods of application 14

1. General discussion 14

(a) Weather conditions 14

(b) Roof deck 25

(c) Valleys 26

(d) Edging 26

ABSTRACT

Asphalt-prepared roofings are defined, their develop- ment is sketched briefly, and recent statistics of production are presented. Factors which influence the choice

of roofing materials generally are discussed. Materials used in the manufacture of asphalt-prepared

roofings and the processes of manufacture are described. Analyses of typical roofings are shown.

Factors which should be considered in purchasing

asphalt-prepared roll roofings and shingles are discussed,

and illustrated graphically for types of shingles that are used most generally. Methods of application and

maintenance are described, and the weathering of as- phalt-prepared roofings is discussed.

Page

VI. Methods of application—Con.

2. Roll roofings 26

(a) General instructions 26

(b) Pitch of the roof 27

(c) Horizontal application 27

(d) Blind naihng 27

(e) Vertical application 28

(f) Hips and ridges 28

(g) Flashings 28

3. Asphalt shingles 29

(a) Pitch of the roof 29

(b) Underlay 29

(c) Edging and starting strips 29

(d) Nails and clips 30

(e) Hips and ridges 30

(f) Flashings 30

(g) Methods of applying particular types of shingles 31

(1) Individual shingles

American method 31

(2) Individual shingles

Wide-space, hexagonal, and Dutch-lap

methods 31

(3) Square- butt strip

shingles 31

(4) Hexagonal-pattern

strip shingles 31 VII. Weathering of asphalt-prepared roofings^ 32

VIII. Maintenanceofasphalt-preparedroofings_ 32

1. Smooth-surfaced roofings 32

2. Mineral-surfaced roofings 33 IX. Specifications 33

I. INTRODUCTION

1. Historical

The asphalt-prepared roofing industry had its beginning in Sweden more than a century ago, when roof boards were covered with paper

treated with wood tar. Later, in Germany,

paper was coated with varnish, surfaced with

finely ground mineral matter, and used as a roofing material. In the United States, asphalt was used to waterproof duck fabric in the early part of the

[1]
nineteenth century. The first recorded use of melted asphalt for impregnating duck fabric in

this country was in 1844. About tliis time roofs

composed of sheets of sheathing paper treated

with pine tar and pine pitch, and surfaced with

fine sand, were being laid. Coal tar and coal- tar pitch were later substituted for the pine tar. These were the forerunners of the present

asphalt and coal-tar-pitch built-up roofs.

It is not known definitely when felt was first substituted for sheathing paper or when asphalt was first used as the impregnating agent, but

it is known that the first asphalt-prepared

roofing, that is, roofing manufactured ready

to apply, was marketed in 1893. The first roofings were unsurfaced.

Mineral-surfaced, asphalt-prepared roofings

appeared in 1897. The first asphalt shingles,

mineral-surfaced, were made in 1901, and about

this time slate graimles were first used as a surfacing material. Asphalt shingles did not come into general use until about 1911.

During 1939, thirty-two manufacturers, rep- resenting about 95 percent of the asphalt-prepared roofing industry, produced 34,225,187

squares ^ of prepared roofing. Almost onethird of this, 11,173,856 squares, was in the

form of asphalt shingles, which are used principally for roofing dwellings. The shingles

produced in 1939 were sufficient to cover more

than 1,000,000 dwellings, assuming an average

size of 10 squares per roof. In two surveys of roofing materials in 20

Eastern States,- made during 1938, the kinds

of roofing materials on 20,841 dwellings along

4,038 miles of liighway were tabulated. Of

these dwellings, 6,549 were roofed with asphalt

shingles and 2,381 with asphalt roll roofing.

Thus almost 43 percent of these dwellingg were

roofed with asphalt-prepared roofings. Statistics of the Bureau of the Census indicate that

asphalt-prepared roll roofings and shingles constituted slig:htly less than half of all the roofing

materials sold during 1937.

It is apparent from the foregoing that this

1 A square of roofing is material sufficient to cover 100 square feet of roof surface. The term "square" is also used in the industry to indicate

100 square feet of roof surface.

3 Hubert R. Snoke, and Leo J. Waldron, Building Materials and

Structures Reports BMS6, Survey of Roofing Materials in the Southeastern States; and BMS29, Survey of Roofing Materials in the Northeastern States. See cover page iii.

industry has grown to enormoiis proportions

vv'itliin a relatively short period.

2. General

The fundamental function of any roof is to protect the interior of a structure, its contents and occupants, from the weather. The property most desired in roofing materials is waterproofness, both initially and during long periods

of exposure. Some factors other than waterproofness that influence the choice of roofing

materials are weather resistance; appearance;

fire resistance; ease of application; weight;

availability; and cost, initial and ultimate.

No attempt has been made to list these factors

in the order of relative importance. Initial

cost, particularly, is an extremely potent factor, as evidenced by the widespread use of low-cost

materials. Proof that availability is a governing factor is furnished by the almost exclusive use of slate roofs in regions where slate quarries

are located. The ready availability of asphaltprepared roofings, with more than 90 plants

making them in 25 States, contributes to their

extended use. Fire resistance is also important;

fireproof and fire-resistant roofing materials are given lower insurance rates; also, building codes

usually restrict the use of roofing materials in congested areas on the basis of fire resistance.

Ease of application is of great interest to home

owners who wish to apply their own roofs, or

in any case where the cost of labor is important.

Appearance has always been emphasized as an

important factor and, apparently, is becoming

increasingly more important.

Asphalt-prepared roofings generally may be

classed as being suitable for low-cost house

construction. They have been made readily

available throughout the country, are relatively

easy to apply, and may be obtained in a variety

of weights up to 375 pounds per square. When

made and applied according to the specifications

of the Underwriters' Laboratories, Inc., these

roofings are eligible to receive the class C label,

which identifies them as being "effective

against light fire exposure", that is, they are "not readily flammable and do not readily carry or communicate fire; afford at least a slight

degree of heat insulation to the roof deck; do not

3 List of Inspected Fire Protection Equipment and Materials, Janu- ary 1940, Underwriters' Laboratories, Inc., 207 E. Ohio St. Chicago, 111.

[2]
slip from position ; possess no flying brand hazard

;

and may require occasional repairs or renev.^als

in order to maintain their fire-resisting properties." Since they are manufactured products, as- phalt-prepared roofings may be obtained in many designs and in a wide range of colors. They are inherently waterproof, but, in com- mon with other roofing materials, the waterproofness of roofs constructed from them depends largely on the design of the roofing and

the skill with which it is applied. Asphaltprepared roofings as produced today are weather-resistant, but they are not unaffected by

exposure to the weather. No definite state- ment can be made concerning the useful life of these materials, for this will vary in dift'erent locations and with the conditions of exposure in the same location. They have been available

generally for only about 30 years, and during

that time a great many have been replaced or

recovered.

The literature on asphalt-prepared roofings is relatively meager, owing to the fact that they

have been developed within a comparatively

short time, a considerable part of which might

be described as a period of development. At

present, the raw materials and manufacturingprocesses are more or less standardized, yet the

producers of asphalt-prepared roofings are constantly investigating new and dift'erent raw materials, new designs of shingles, and neAV and

improved processes of manufacture.

Any manual that would attempt to furnish

detailed information concerning all prepared

roofings would, therefore, soon be out of date. The purpose of this publication is to discuss the

subject of asphalt-prepared roofing in general

terms, and to give some detailed information

t| concerning fundamental factors that should be

considered in purchasing any type of prepared

J roofing, with particular reference to certain

1 definite kinds that may be classed as standard

jj types, since they are produced by practically

1 all the manufacturers.

J The average owner of a dwelling usually gives

|1 but little consideration to his roof until it needs

, repair or replacement and, consequently, has

I but little knowledge of roofing materials in

general. Unfortunately, the salesman who at- tempts to sell him a new roof may be but little,

if any, better informed. As a consequence,

price is too often the determining factor. Without question, many purchasers of inferior roofing materials would actually prefer the better

materials if the advantages of the bettci' materials were made plain.

II. DEFINITION OF ASPHALT-PREPARED ROOFING

Asphalt-prepared roofing may be defined as roofing made with a felt base, impregnated

with asphalt, and coated with a more viscous

asphalt than that used in impregnating the

felt. It is marketed ready to apply, cither as long strips in rolls called roll roofing or in the

form of relatively small pieces known as

shingles. The roll roofing may be dusted on

both sides with fine mineral matter, such as

talc, mica, or fine sand, to prevent sticking in the rolls; or it may be coated on only one side

with fine mineral matter and have coarse mineral granules embedded in ' the asphalt coating on the surface to be exposed to the weather.

The first type is described as smooth-surfaced

prepared roofing, the second as mineral-surfaced prepared roofing. Asphalt shingles are always mineral surfaced.

Several terms are used to describe these

materials. Both smooth- and mineral-surfaced

roll roofings are described as composition or ready roofings. Smooth-surfaced roofuig is known as smooth roll roofing, paper roofing,

tar-paper roofing, and, sometimes, as rubber

roofing. Mineral-surfaced roofing is also known

as grit roll roofing and slate-surfaced roofing.

Asphalt shingles are described as composition

shingles, slate-surfaced shingles, and, fre- quently, as asbestos shingles, though com- monly they contain no asbestos fibers.

III. MATERIALS USED IN ASPHALTPREPARED ROOFINGS

1. Felt

The felts used in asphalt-prepared roll roofings may be made from organic or asbestos

fibers; those in asphalt shingles are almost in- variably from organic fibers. Felts of both

types are formed on a machine similar to that

used in the manufacture of paper.
Felts made from organic fibers are usually

described as "rag" felts, because they contain

a large proportion of fibers obtained from

graded rags. Originally, materials other than

rags, particularly wood fibers, were considered

as adulterants, but research has shown that

roofings made from felts containing as much

as 50 percent of certain materials other than

rags may resist weathering as well as if not

better than those made with all-rag felts.* Analyses of typical organic felts are shown

in table 1.^ Table 1.

Fiber analysis of typical felts

Sample

No. be

ct Pi

Ground wood

Chemical wood

Jute

Wool Rayon

1

Silk

Hair

Kapok

Pet. Pd. Pet. Pet. Pet. Pet. Pet. Pet. Pet.

1 53.5 16.9 8.3 11.8 2.3 4. 5 1.6 0.8 0.3

2 50. 7 17.8 8.2 10.2 4. 7 1.6 3.0 .3 3. 5 3 77.5 2.0 7.5 5: 5 1.5 4.3 0.4 .6 4 59.3 6. 2 9.2 10.2 7.1 2. 5 3.3 1. 6

5 50.2 18.8 13.3 4.6 0.5 6.6 3.9

6 -- 55.4 11. 2 14.0 14.9 1.5 1.9 0.7 0.

1

65.8 17.3 5.3 6. 9 3.6 0.5 .4 .3 sl'/....'.... 54.5 5.2 18.3 8.8 1.5 9.6 1.9

Roofing felts are designated in the industry

by "numbers" which are their weights in pounds

per 480 sq. ft. Specifications for asphaltprepared roofings usually specify the weight

per 108 sq ft of felt. Typical felts used com- monly in prepared roofings are shown in table 2. Felts made entirely of asbestos fibers are not

so satisfactory for the manufacture of pre- pared roofings as those containing some hair or cotton fibers, which tend to give the felts a more open texture and thus permit them to absorb more asphalt. Some binding material,

such as starch, glue, dextrine, or alummum

silicate, is also necessary. Specifications for asbestos roofing felts usually require a minimum

of 85 percent of asbestos fibers. Weights of asbestos felts are expressed in pounds per 108

sq ft. 2. Asphalt

The asphalts used in prepared roofing are mainly of petroleum origin, that is, they are obtained as residues from the distillation of crude petroleum in the production of gasoline,

fuel oil, lubricating oil, etc. Some natural

asphalts are also used.

' O. G. Strieter, J. Research NBS 16, 511 (1936) RP888. 'Hubert R. Snoke and Braxton E. Gallup, J. Research NBS 18, 669

(1937) RP1002.

Petroleum asphalts of semisolid consistency,

and free from mineral matter, are used to impregnate the felts. The impregnating asphalt

is Imown as the "saturant". The weight of saturant is always expressed in terms of the

weight of the dry felt as "percentage saturation".

Thus a saturation of 175 percent indicates a weight of asphalt 1% times the weight of the

dry felt, or, a saturated felt weighing 30 lb per 108 sq ft and having a saturation of 175

percent is composed of 10.9 lb of felt and 19.1

lb of asphalt.

Asphalts used for coating the felts are usually

harder and always more viscous than those

used as saturants. Roof temperatures of 140° F and higher are not unusual. Coatingasphalts must not flow nor slip when exposed

to these temperatures. The coatings of mineral-surfaced roofings are protected somewhat

by the surfacing granules, but they must be

able to hold the granules in place under the

maximum temperatures that may be reached on a roof. Coating asphalts usually contain fine mineral

filler, which, in the case of petroleum asphalts,

is added in order to increase the weather resist- ance of the coating. Mineral fillers added to coating asphalts were considered as adulterants

in the early manufacture of prepared roofings.

Research has shown, however, that the addition

to coating asphalts of certain fine mineral fillers in proper proportions will definitely increase

their resistance to the weather.^

3. Surfacing Materials

Pulverized slate, talc, slag, and mica were among the first materials to be dusted on

asphalt-prepared roofing to prevent sticking

and also to produce a more uniform appearance.

Talc and mica, both coarse and fine, are used

for the same purposes today on smooth-surfaced prepared roofings and on the back of mineral-surfaced roll roofings and shingles.

The first use of larger surfacing granules was

probably prompted by the added resistance to

fire imparted by them. Fine gravel and feld- spar chips were used originally, roofings sur- faced with them being marketed about 1897.

Crushed slate was used first about 1902 on roll roofings and about 1910 on asphalt shingles.

» O. G. Strieter, J. Research NBS 30, 159 (1938) RP1073.

[4]
Crushed porcelain, brick, tile, and pottery were

also among the early surfacing materials that were used to prothice diverse color effects. Prepared roofings in diff erent colors and color

combinations proved immediately popular.

Consequently, a great amount of research has

been employed in the development of synthetic

surfacing materials, particularly those of bril- liant colors not obtainable from the natural

rocks or common ceramic materials.

Several types of colored granules are now in general use—namely, natural, fired, glazed, sili- cated, and cemented. Granules colored with

baking enamels, lacquers, or stains were used

formerly but have since been abandoned.

Natural granules are those obtained by crushing slate or other colored rocks, such as shale,

quartz, greenstone, etc. Fired granules are those produced by firing- certain clays or shales at high temperatures,

with or without the addition of metallic oxides

to produce colors. Glazed granules are made from somewhat

porous refractory rocks, such as quartzite. A

common method is to treat the rock, screened

to proper size, with a water-soluble glaze composed of a coloring agent and a fluxing agent.

After drying, the granules are fired at a temperature from 1,000° to 2,200° F. At present

most of the synthetically colored granules are made by this or a somewhat similar method.

Silicated granules are those in which sodium

silicate is used as the fusing and glazing agent

in combination with coloring agents. Silicated

coatings are frequently applied to slate granules.

Cement-coated granules are those coated with

a cementing mixture which forms a hard insol- uble coating, either at normal or elevated

temperatures.

4. Composition of Typical Roofings

Specifications for asphalt-prepared roll roof- ings and shingles issued by the Federal

Government, the American Society for Testing

Materials, and the Underwriters' Laboratories,

Inc., are listed at the end of this report. The

Federal Specifications and those of the American

Society for Testing Materials are limited in

their requirements to the composition and

weight per unit area of the material. Those

of the Underwriters' Laboratories, Inc. include

requirements for the composition and weight

of the material and also recognize certain fea- tures of application.

Roofings of the same type, produced by

diff'erent manufacturers, show but little variation in composition. There are several reasons

for this uniformity. From the beginning the

asphalt-prepared roofing industry, although

highly competitive, has established standards

of weight for their finished products of the same class. The fundamental parts of the

machines used to produce these roofings are complicated and expensive, and are available

from only a few sources. Sources of supply of

felt, surfacing granules, and min(>ral fillers are somewhat limited, so that it is not unusual for several producers to obtain these materials from

a common source. Another factor that tends

to produce uniformity of composition in materials from large and small manufacturers is the inspection service conducted by the Lenderwriters' Laboratories, Inc., in connection with

their labeling service. Prepared roofings must

comply with the minimum requirements of the

Underwriters' Laboratories as regards composition and application in order to be eligible for the class C label.

Table 2.Smooth-surfaced asphalt-prepared roll roofings ^

Sample No. Grade Weight

of felt

"Number"

of

felt

Saturation

Weight

of satu- rant

Weight

of coat- ings and

fine sur- facing

Weight

of roofing

lb lb/108 ft' % Ib/lOSft'- lb/108 ft^ lb/108 ft

1 1 6.7 30 150 10.0 15.8 32.5

2 4.7 21 150 7.

1

20.2 32.0

3 1

35 < 7.6 34 157 11.9 12.5 32.0

4 6.5 29 145 9.4 16.1 32.0

5 [ 4.5 20 150 6.8 21.7 33.0

6 1 7.9 35 150 11.9 22. 7 42.5

8.1 36 155 12.6 21.3 42.0

8

1 45 } 11.3 50 162 18.3 12.4 42.0

9 9.5 42 164 15.6 16.9 42.0

10 J 11.7 52 175 20.5 10.8 43.0 U. 1 11.3 50 160 18.

1

23.

1

52.5

12 11.3 50 186 21.0 19.7 52.0

13 1

55 } 13.0 58 181 20.5 18 5 52.0

14 U.9 53 183 21.8 13.3 47.0

15 J 11.7 52 175 20.5 20.8 63.0

16 , 13.5 60 165 22.3 26.7 62.5

17 14.6 65 195 28. 5 18.1 62.0

18 1

65 \ 14.2 63 185 26.3 21.5 62.0

19 13.5 60 165 22. 3 21.2 57.0

20 I 12.2 63 185 26.3 22.5 63.0

21 f 16.4 73 175 28.7 28.4 73.5

22 16.9 75 195 33.0 22.1 72 0 23 i 16.

2

72 191 30.9 24.9 72.0

24. ... 14.0 62 180 25.2 27.8 67.0

25 I 14.2 63 185 26.3 32.5 73.0

1 The 35- and 45-pound grades are not eligible for the class C label of the Underwriters' Laboratories, Inc.

[5]
The composition of representative smoothsurfaced asphalt-prepared i-oofings and asphalt

shingles is shown in tables 2 and 3, respectively.

In table 2, each roofing listed in the several

grades, represents a different producer. The

shingles in table 3 are those from which the

felts reported in table 1 were taken, the samples

being numbered identically in the two tables,

each sample representing a different producer.

The uniformity of composition of these shingles

may also be taken as representative of that of mineral-surfaced roll roofings.

Table 3.

Composition of typical asphalt shingles

Sample No.

Color

Felt Asphalt Mineral matter 1

Weight

"Number"

of

felt

(calculated)

Saturation

1

j

Thickness

Ash

Weight

of

saturant

Top

coating

Bottom

coating

Top

Bottom

Granular surfacing material Mainly fine mineral filler

Retained

on

No.

70

sieve Type

Passing

No.

70

sieve

(percent

of

coating) Nature of mineral matter passing No. 200 sieve

ibim Per- Per- ibim IbjlOS Ib/lOS ibim IblWS Ibim

fn cent in. cent ft' fP ft' ft' m ft' 1 Natural green 10. 4 46

49

192 0. 049 9.8 20.0 18.9 0.9 36.8 0.7 28.9 Slate 32.9 » Silicate rock. 2 Natural red _ .

. . n. 1 205 .057 9.

1

22.8 17.6 1.

1

34.7 .5 29 6 ....do 26.0 Quartz.

3 Ceramic bright 11.8 52 195 .058 8.3 23.0 14.9 2.7 33.2 1.5 28. 9 Quartz with fluxed 26. 7 Dolomitic-Mmegreen. green coating. stone.

4 Blue-black 11.2 50 160 .051 8.3 17.9 19.3 4.0 31.9 2.6 22.2 Slate 35.6 Silicate rock, also

slate flour. 5 Ceramic green..

_

10.4 46 190 .054 11.0 19.8 14.2 5.0 33.7 2.0 29 6 Quartz with fluxed 29.4 Black slate flour. green coating.

6 Natural red 11.7 52

56 182 .052 8.0

8.8

21.3 15.

1

0.9 37.2 1.2 29.9 Slate 36.3 Ground quartz.

7 Natural blue- 12.5 169 .057 21.1 16.8 1.7 33.8 0.8 25.5 do 34.9 Dark slate flour. black.

8- do 12.4 55 201 .061 8.

1

24.9 26.

1

1.2 22.4 1.6 21.8 do 9.6 Do.

• Ground rock in which basic minerals predominate. The relative importance of the details of composition are not discussed at length here,

because the average purchaser has little opportunity to judge these materials from the standpoint of composition. Also, the composition of prepared roofings furnishes no sure criterion

of their behavior when exposed to the weather.

Asphalts used as saturants and coatings, obtained from different sources, or from the same

source but refined by different processes, pro- duce roofings which behave dift'erently on

exposure. Roofings made from identical materials but with vai'iations in the manufacturing

process do not behave similarly.

Proper saturation is one of the most important details of composition. The voids in the

felts of commercial roofings are never filled completely with asphalt, but the more nearly a

felt approaches complete saturation, the better

the service it will render. Felts that are not

saturated adequately absorb water readily, and

roofings made from them are likely to warp and

blister on exposure. A light-weight felt satu- rated adequately is always more desirable than

a heavy felt saturated inadequately. Reference

to tables 2 and 3, and to the specifications listed at the end of this report, indicates that the

heavier grades of roll roofings and the asphalt

shingles carry the greatest saturation. Asphalt

shingles, particularly, should be well saturated

because the ratio of the exposed cut edges to the area is much greater with shingles than with

roll roofings, which makes the possibility of moisture absorption through the edges of the

shingles proportionately greater.

Asphalt coatings that adhere well to the

saturated felt and to the granular surfacing

materials should be used. In order to insure

proper adhesion of the coating asphalt to the

saturated felt, the asphalts used as coatings and

saturant should be "compatible", that is, they

should show no separation, either initially or

after prolonged exposure.

IV. MANUFACTURE OF ASPHALT-PREPARED ROOFINGS

Asphalt-prepared roofings are usually manufactiued on high-speed, continuously operat-

[6]
ing machines. In the simplest form of machine

the felt enters as a dry sheet and passes over

preheating rolls into the saturator, where it is thoroughly impregnated with asphalt. The

saturated felt then passes through a looping

system, where it is cooled somewhat, to the

coating rolls, where the asphaltic coatings are applied to both sides of the sheet. While the

coatings are still hot, the sheet is passed by the

granule feeders where the mineral surfacing

materials are applied, through rolls which embed

the surfacing materials firmly in the coating.

Then follows a series of cooling rolls and a looping device, which serve to cool the sheet before

it passes to the automatic cutter and winder,

if it is to be marketed as roll roofing, or to the

shingle cutting and packaging machine, if shingles are being produced. Machines capable of

producing 250 linear feet of roll roofing per

minute are not uncommon, while some developed recently are said to produce up to 400 feet per minute.

So-called intermittent machines are those in

which the felt is saturated, cooled, and wound

into lai"ge rolls to be coated later. Many variations have been proposed in the

manufacturing process, each intended to secure

a better product or increased production.

Briefly, the composition of prepared roofings

and the processes of manufacture are items

over which the occasional purchaser has no

control, and about which he would not have

sufficient information to serve as a basis for differentiating between the various products of the same class. There are, however, certain

very important factors in the choice of asphaltprepared roofings which are subject to the judgment of the occasional purchaser. Some of these factors are discussed in succeeding sections.

V. FACTORS WHICH SHOULD BE CONSIDERED IN PURCHASING ASPHALTPREPARED ROOFINGS

L Roll Roofings

The preliminary choice in roll roofings is between the smooth- and mineral-surfaced varieties. Smooth-surfaced roofings generally have

the lowest initial cost and have the least to recommend them from the standpoint of appearance. They are subject to more rapid dcstei-io- ration because the asphalt coatings are not piotected from the action of sunlight. If they are properly maintained (section VIII-1), they

may render service equal to that of the mineralsurfaced roofings.

Smooth-surfaced roll roofings are marketed in several different weights per 108 sq ft, this being the amount necessary to cover one square

of roof surface. The additional 8 sq ft is required to provide for lapping the sheets. The felt used as a base largely governs the

finished weight of the roofing. Reference to table 2 will show that the weight of felt may

vary considerably in roofings of different manufacture, particularly in the lighter weights of smooth-surfaced roofings.

The lighter weights of roll roofings (35- and

45-lb) are not recommended for any but the

most temporary of structures. They are used

advantageously as underlay materials for other

roofing materials, such as slate, tile, and

cement-asbestos shingles. The Underwriters'

Laboratories, Inc. do not extend label service to smooth-surfaced roll roofings weighing less than 50 lb per 108 sq ft. The standard grades of mineral-surfaced roll roofings are made on a felt base weighing not

less than 48 lb per 480 sq ft. They have several

advantages not possessed by the smoothsurfaced varieties. One of these is color. Originally these roofings were made in solid colors only, but at present they may be obtained

in a number of colors and color combinations,

either in solid areas or blended. Occasionally,

granule's of a dift'erent color are used to stencil

patterns which simulate the appearance of shingles.

The mineral-surfacing granules protect the

asphalt coating from the action of the elements

and thus insure longer life. Another advantage

is that these roofings are more fire-resistant

than smooth-surfaced roofings. Because of

their greater weight, they present a smoother

appearance on a roof deck.

In order to relieve the monotony of the

smooth, uniform appearance of mineral-surfaced

roll roofings, one edge of the sheet is sometimes

cut so that it will produce a regular pattern on

a roof. Figures 5 and 6 illustrate two common

types of designs. It will be observed that by

286109°—41 2 [7]
increasing the lap of the sheet shown in figure 5 a regular hexagonal pattern will be produced.

These are more expensive than roofings of the same weight per unit area but made with

straight edges, because more material is re- quired per unit area of roof. They usually

have a greater lap than the roofings with

straight edges, but lacking an unsurfaced

lapping edge, the laps cannot be cemented as securely and the heads of the nails must be

exposed.

Instructions for applying roll roofings are given in section VI-2, pages 26-28. Methods

of application are illustrated in figures 1 to 6, inclusive.

Most roll roofings are essentially singlethickness coverings, that is, the greater part

of the roof area on which they are laid is covered by but a single layer. The chief

advantage of asphalt-prepared roll roofings is that, when applied properly, they present a continuous unbroken fabric over the entire

roof deck. A disadvantage in any single-ply

roof is its greater liability to puncture from

accidental causes.

2. Asphalt Shingles

(a) General Discussion

The development of mineral-surfaced as- phalt-prepared roofings marked a considerable

advance over the smooth-surfaced roofings

from the standpoint of appearance, yet they

left much to be desired in this respect when

considered as a roofing material for dwellings.

The development of asphalt shingles followed

as a natural consequence. The American

public was thoroughly familiar with shingletype roofs because of the wide use of wood

shingles and slate. Metal shingles also pre- ceded asphalt shingles, and certain designs of asphalt shingles were developed originally for metal shingles. Asphalt shingles provided a

relief from the monotonous appearance cl the

roll roofings. In most cases they furnish better

fire and weather resistance because of the

multiple layers of fabric. Their development

gave great impetus to the asphalt-prepared

roofing industry, not only because shingle-type

roofs require more material per unit area of roof but also because shingles are acceptable

on many more structures, owing to their greater

artistic value.

The first asphalt shingles were cut by hand

from roll roofings. They were rectangulai' in shape, and were laid by the so-called "American" method, which is the same as that used in laying wood shingles and slate (figs. 7 and 8). Single-unit shingles are described as "individual" shingles, to distinguish them from multipleunit shingles, commonly called "strip" shingles,

which were developed later. Asphalt shingles have been produced in a

multiplicity of shapes, since manufacturers have

vied with each other from the early days of the

industry, to produce individualistic shingles

with exclusive features.' Space is not available to discuss all the

different designs of asphalt shingles in detail. In general, variations in design have been

intended to

:

Produce different patterns (rectangular,

hexagonal, octagonal, circular, reversible

shingles)

.

Facilitate application (guide marks, tabs,

etc)

.

Give shingles a more massive appearance

(shadings, thick butts).

Secure the butts of shingles (metallic

fasteners, slits, folds).

Require less material per unit area. Since asphalt shingles are fabricated products,

they may be made in any shape or size within

manufacturing limits. It was soon discovered

that multiple-unit shingles oflPer certain eco- nomic advantages over individual shingles,

chiefly because they may be applied more

rapidly and accurately. They are composed of two, three, or four units joined together (figs. 12 to 16, inclusive). Since they are made up of a number of individual units, the patterns

formed by strip shingles are substantially the same as those formed by individual shingles, and

variations in the design of strip shingles have

been made for the same purposes as those listed under individual shingles.

Three general types of shingles, from the

standpoint of weight and thickness, are in

' Numerous references to the patent literature on asphalt-prepared

roofings and shingles are given in Asphalts and Allied Substances, 4th ed.

p. 1327-1396. by Herbert Abraham, published by D. Van Nostrand Co.,

Inc., New York, N. Y. (1937).

[8]
common use. They are (1) standard-weight,

(2) heavy-weight, and (3) thick-butt. The

standard- and heavy-weight shingles differ principally in the weight of the felt used as a

base. The heavy-weight shingles are thicker

and consequently more rigid, than those of standard weight.

Thick-butt shingles (figs. 14 and 15) are a comparatively recent development. They are made on felts of standard or lighter weight with

the butts, for a distance slightly greater than

the exposure, somewhat thicker than the re- mainder. This increased thickness is accomplished by applying additional layers of asphalt

coating and granular siu-facing materials. When

the additional layers of coating and granules

are applied to the exposed surface only, they

are described as overlaj^ shingles. Another

type of thick-butt shingle is made by dipping

the butts of the shingles into molten asphalt and

embedding granules in this layer of asphalt , thus

providing two layers of asphalt coating and two

layers of granular surfacing material on the

surface to be exposed to the weather, and two

layers of asphalt and a layer of granules on the

under side of the shingle. The dipping process

seals the edges of the shingle that are to be

exposed to the weather. This extra dipping and

application of granules are done by hand so that shingles of this type are comparatively

expensive.

The chief advantage claimed for thick-butt

shingles is that they resist weathering better

because of the extra layers of granules and

coating on the exposure surface. The thicker

butts, particularly of those with granules on

both surfaces, give heaver shadow lines on the

roof. The multiplicity of designs and weights of individual and strip shingles that are available,

and the various methods of laying both types

of shingles, but particularly individual shingles,

produce a picture that is confusing to the aver- age home owner. Some of the more important factors that

should be considered when purchasing asphalt

shingles are defined and explained in the suc- ceeding section. These factors are illustrated

by drawings of sections of roofs laid with some

of the common types of shingles, figures 7 to 16. These factors are coverage, headlap, sidelap,

exposure, and weight p<>.r unit at-ea of roofing

material, and, more particularly, per unit area

of finished roof. These factors are applicable

to all kinds of roofing materials that are applied

in the form of shingles. Appearance is an important factor also, but it will not bo discussed

under this heading because it is entirely a matter

of personal preference.

(b) Coverage

The term "coverage", used in connection

with roofs, is more easily explained than defined. Asphalt-prepared roll roofings are doscribed as "single-coverage" roofings because

they provide but a single layer of material over

the greater part of the roof area. Shingles in- variably are small units laid so that they overlap shingles in the course, or courses, below,

and in certain cases, shingles adjacent to them.

Roofs constructed of shingles therefore are made up of areas covered by one to four layers, or plies, of material, depending on the size and

shape of the shingles and the method by which

they are applied. These areas, designated as

one-, two-, three-, or four-ply areas, and ex- pressed as percentages of the whole roof area, constitute the distribution of coverage, or more

simply, the coverage of the shingles.

Calculation of coverage must be made on the

basis of a unit which is repeated over the entire

surface of the roof. For individual shingles

laid by the American method, figures 7 and 8, the simplest unit is one exposed tab, or butt,

and one space between two exposed tabs. The

coverage diagram in the lower right-hand corner

of figures 7 to 16, inclusive, represents the re- peating unit for each design of shingle illus- trated and shows graphically the distribution

of coverage.

Knowing the extent of the areas covered by

the difi'erent numbers of layers, it is a simple

matter to calculate the total area of fabric

required per square of finished roof. Thus

individual shingles 9 by 12% in. in size, laid as

illustrated in figure 7, fm-nish approximately

the following coverage: Four-ply, 17 percent;

three-ply, 73 percent; two-ply, 6 percent; oneply, 4 percent; or, in one square of finished roof

68 sq ft of fabric in the four-ply area; 219 sq ft in the three-ply; 12 sq ft in the two-ply; and

4 sq ft in the one-ply—a total of 303 sq ft.

[9]
The same shingles laid by the so-called widespace method (illustrated in fig. 9) fm'nish the

following distribution: Four-ply area, 4 percent;

three-ply, 16 percent; two-ply, 48 percent;

and one-ply, 32 percent; or, in one square of finished roof 16 sq ft in the four-ply area; 48

sq ft in the three-ply; 96 sq ft in the two-ply;

and 32 sq ft in the one-ply—a total of 192

sq ft. In each case, the number of shingles

required for one square of finished roof is obtained by dividing the area of one shingle

into the total area of roofing material required

for one square.

It is practically impossiljle to determine the

coverage of the difl'erent types of shingles by

calculations based on visual inspection. A

simple, practical method is to cut miniature

shingles, drawn to proper scale, from trans- parent paper or tracing cloth, fasten them to a transparent background, and view them by

reflected light. The number of layers of

fabric at any point will be immediately apparent.The American method of laying, illustrated

in figures 7 and 8, furnishes the best coverage

of any of the methods utilizing individual

shingles. The method shown in figure 8, with the first and fourth courses of shingles in

line, provides a slightly better distribution of coverage than that shown in figure 7, with

alternate courses in line. Both of these methods are entirely satisfactory.

The wide-space method, illustrated in figure

9, requires the same shingles as the American

method, but spaces them at much greater dis- tances, usually 6 in. for a 9-in. shingle. Consequently but 240 shingles, 9- by 12%-in., are required per square when laid by this method,

as compared with 380 when laid by the American method. Stated differently, the American

method requires 58 percent more fabric per

square. Also, almost one-third of the area of roofs laid by the wide-space method is covered

by but a single layer of fabric. This method

has been used principally for reroofing and

is not widely used at present.

The hexagonal, or French, and the Dutchlap methods of laying individual shingles,

figures 10 and 11, are little better than roll roofings from the standpoint of coverage.

These methods are not recommended by

manufacturers for new roofs, but many have

been used in this manner. They have been

and are being used widely for reroofing.

^Vhen laid, strip shingles furnish practically

the same patterns as individual shingles, and

may be considered as individual shingles that

have not been separated. The portions that are cut away to form the tabs, commonly called

"cut-outs", extend only the length of the ex- posed tab, whereas in individual shingles the

corresponding space extends the entire length

of the shingle. Square-tab strip shingles with

talis the same width as individual shingles, and

of the same length, therefore furnish slightly

better coverage than the latter; The patterns

shown by figures 7 and 12 are almost identical,

yet the coverage of the strip shingle illustrated

in figure 12 is somewhat better than that of the

shingles shown in figure 7, although the latter are M in. longer. This should not be construed

as a blanket indorsement of strip shingles over

individual ones laid by the American method,

because other factors must be considered.

Shingles laid as illustrated in figures 7 and 8

require 760 nails per square, whereas those shown

in figure 12 normally are laid with 500 nails. The individual shingles are fastened more se- curely than the strip shingles, but the latter may be applied more cheaply because they re- quire fewer nails and less labor. Individual

shingles, being small units, each nailed separately, do not show as readily as do the largerunit strips any changes that take place in the

roof deck, such as are caused by warping of unseasoned sheathing boards.

Individual shingles are frequently provided

with self-spacing features, consisting of projections on one side and corresponding recesses on

the other. The coverage of such shingles is the same as that of strip shingles which are of the same length and which are exposed the same

distance.

The relation of coverage to waterproofness is obvious. Shingles that provide approximately

three layers of fabric over the entire surface of a roof may be weathered so badly that the granular surfacing material and asphalt coating have

disappeared entirely from the exposed surface,

yet the roof will not leak because of the layers

of unweathered fabric beneath.

Roofers state frequently that individual or

[10]
strip shingles that provide but single coverage

over a large proportion of the roof area are

entirely satisfactory for reroofing purposes over weathered wood or asphalt shingles. They may

render satisfactory service when the roof is new,

but, actually, shingles that furnish single cover- age are no more durable than the single layer of

fabric. Numerous observations in the field have

sll0^vn that the oldest roofs are almost invariably of shingles that furnish the best coverage.

Most complaints of imsatisfactory waterproofness arise from shingles that provide poor

coverage.

Shingles that furnish the best coverage have

the highest fh^st cost, because they require more

material per unit area of roof and more labor to apply them. The better the coverage, the

greater the insulation effect of shingles, although

it is true that the insulation value of the best

asphalt shingles, like that of most roofing materials, is very slight when compared with that

of materials that are used regularly for heatinsulation purposes.

The fire resistance of multiple-layered as- phalt-prepared roofings is greater than that of single-coverage roofings.

(c) Headlap

Headlap, in shingle-type roofs, is usually

defined as the distance a shingle in any course

overlaps a shingle in the second course belo^\^ it . However, with shingles laid by the Dutch-lap

method, figure 11, where no shingle overlaps a

shingle in the second course below, the headlap

is taken as the distance a shingle overlaps one m the next course below. A more proper defini- tion of headlap is the distance water must

travel upward from the outside to the inside of a roof, assuming there are no breaks in the

fabric. This latter definition emphasizes the

importance of headlap to the waterproofness

of a shingle roof. The headlap of individual shingles laid by the

American method, and of strip shingles, may be

determined by subtracting twice the distance a

shingle is exposed from its full length.^

'The use of the terms "length" and "width" in connection with

individual and strip shingles may be somewhat confusing. In this discussion, length is understood to mean the vertical dimension of a

shingle when laid on a roof. In individual shingles, except those laid by the Dutch-lap method, this is greater than the horizontal dimension;

in strip shingles and individual shingles laid by the Dutch-lap method,

it is less than the horizontal dimension.

For example, the shingles shown in figui-es 7 and 8 are 12^4 in. in length and are exposed 4 in.; the headlap is therefore 4% in. Those in figure

16 are 11^ in. in length and are exposed 4% in.; the headlap in this case is but 2 in. In figures 13 and 14 the headlap is also 2 in. The headlap

of the shingles illustrated in figures 7 to 16 is designated in each case as the distance ab. An important consideration in determining

the waterproofness of shingles of dift'erent design and laid by dift'erent methods is the lateral distance that may be said to be vulnerable to

deficiencies in headlap. Unfortunately, in most

shingles where this distance is comparatively

great, the headlap is reduced to a minimum. In

individual shingles laid by the American method

this lateral distance is the width of the spacing

between the shingles. In square-tab strip shingles it is the width of the sections that are cut out to form the tabs, usually }4 or % in. in standard-weight shingles, and % or 1 in. in heavvAveight shingles. In strip shingles that

provide a hexagonal pattern when laid, this dis- tance is greater than for the square-tab shingles.

For the 11)3- by 36-in. shingles shown in figure

16, it is 4 in. This distance is greatest in shingles laid by the Dutch-lap method, it being 10

in. for these shown in figure 11.

(d) Sidelap

Sidelap is defined as the hoiizontal distance one individual shingle overlaps another in the same course. This item is important mainly

with shingles laid by the Dutch-lap, hexagonal,

and wide-space methods. The sidelap is designated as the distance ef in figm'e 9 to 11, in- clusive. A study of these figures will show the

relation of sidelap to waterproofness. Obviously, as the sidelap is increased, coverage is increased.

(e) Exposure

The exposure of a shingle is defined as the

maximum distance, measured on the length of the shingle, that is exposed to the weather, dis- regarding the space between individual shingles

and the cut-out sections of square-tab strip

shingles. In figures 7 to 16, inclusive, the ex- posure is designated as the distance cd. The

exposure of shingles is of primaiy importance

from several standpomts. For a given shingle

[11]
the lieadlap, coverage, and exposure are interdependent; as the exposure is increased, the

headlap and coverage are decreased correspondingly. As the exposure is increased, the possibility of damage from winds of high intensity

is increased.

Individual shingles are furnished frequently

with guide marks to enable the roofer to determine the correct exposure. The self-spacing

features mentioned previously also accomplish

this purpose. The exposure of strip shingles is determined by the length of the portions that

are cut away to form the tabs. This fact greatly

facilitates the laying of strip shingles.

Individual shingles that are laid by the

Dutch-lap or hexagonal methods, where the

greater part of the area of each shingle is ex- posed to the weather, are usually fin-nished with some fastening or locking device to hold them in place. Such devices are also used frequently

with strip shingles that have large exposures,

particularly witli those that give hexagonal

patterns when laid.

(/) Weight

(7) Per unit area of shingle.

The weight per unit area of asphalt shingles, as of prepared roll roofings, is governed largely

by the weight of the felt used as a base. (See

table 3.) Felts weighing 48 to 53 lb per 480

sq ft (Nos. 48 to 53) are used commonly for standard-weight shingles. Felts used for heav}!--

weight shingles may range from 60 to 80 lb per

480 sq ft (Nos. 60 to 80).

The so-called thick-butt shingles are not

uniform in weight throughout, the section that

is to be exposed being covered with an additional layer of asphalt and surfacing granules.

These shingles are usually made on a No. 48 felt. The weight per unit area of the thick-butt sec- tion should be not less than 100 lb per 108 sq ft. Table 3 shows the composition of representative samples of standard-weight asphalt

shingles.

(2) Per unit area of roof. The weight per unit area (square) of roofs

covered with asphalt shingles depends on the

weight per unit area of the shingles, and the

coverage. The common types of shingles on

the market range from 125 to 325 lb per square

when laid and some have been marketed that

weighed as much as 375 lb per square.

Table 4 lists the weight per square of finished

roof for the types of shingles used most generally. These are average weights, which will vary slightly in shingles of the same dimensions

from dift'erent manufacturers.

The different types of shingles have been

classified roughly in table 4 by weight per

square of finished roof. In general, the shingles

that furnish the greatest weight provide the

best coverage, headlap, etc., and may be considered best for durability, waterproofness, and

fire I'esistance. Several types of asphalt shingles provide

practically the same weight per square of fin- ished roof. These are as follows: Individual

shingles, American method, standard weight,

250 lb; square-butt strip shingles, 12}^- by 36-

in., standard weight, 265 lb; square-butt strip

shingles, 12- by 36-in., heavy weight, 257 lb; and square-butt strip shingles, 15- by 36-in.,

overlay type, 254 lb. An intercomparison of some of the features exhibited by these shingles

may be helpful in comparing other types of

shingles. These will be designated as follows:

(a) Individual shingles, 8- or 9- by 12 %-in.,

American method. (Fig. 7.)

(b) Strip shingles, 12^- by 36-in. (Fig. 12.)

(c) Strip shingles, 12- by 36-in. (Not illus- trated.)

(d) Strip shingles (overlay), 15- by 36-in.

(Fig. 15.)

_ Coverage.—There is little difference in coverage

between the a, b, and d shingles, each requiring

about the same area of fabric per square. The

c shingles, although of approximately the same

weight as the a, b, and d shingles, provide

poorer coverage. The area covered by but a

single thickness (single-coverage area) with the

c shingles is so small as to be almost negligible.

The a, b, and d shingles furnish not less than

double coverage at any point, however, and the

greater part of the roof is covered with three

layers of fabric with those shingles, whereas

with the c shingles but 37 percent is covered

with three layers.

Headlap.—The a, b, and d shingles with headlaps of 4%, 4}^ and 5 in., respectively, are

definitely superior in this respect to the c shingles, which have but a 2-in. headlap.

[12]
Cost

per

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13
Exposure.—The a and h sliingies are intended

to be laid with a 4-in. exposure, the c and d with

a 5-in. exposure. There is probably little to choose between the 4- and 5-in. exposures in these cases. The c and (/ shingles are more

rigid than the a and h shingles because of the

greater thickness of the exposed areas, and

therefore would probably not suffer more from

winds of average intensity.

Weight.—As noted previously, the weights

per square of these shingles are practically the

same, so that one has little, if any, advantage

over another in this respect. The a, b, and d

shingles prol^ably furnish greater weights of coating asphalt than the c shingles because of the greater area. The c shingles, by the same

reasoning, probably contain more felt and

saturating asphalt than the other shingles.

However, the a, b, and d shingles furnish a

better distribution of weight, generally, than

the c shingles. This is particularly true of the a and b shingles.

(g) Cost

Representatives of the Home Owners' Loan

Corporation in the cities listed below furnished,

in 1938, the cost figures listed in table 4.

Northeastern States

Wilmington, Del. Philadelphia, Pa. New Haven, Conn.

Boston, Mass.

Manchester, N. H.

Portland, Maine

Rutland, Vt.

Southeastern States

Greensboro, N. C. Columbia, S. C. Savannah, Ga.

Atlanta, Ga.

Jacksonville, Fla. Birmingham, Ala. Knoxville, Tenn.

The cost of application per square (100 sq ft of roof surface) is included in these figures.

The range of costs in each section is shown in

the columns marked "minimum" and "maximum." The minimum and maximum costs were distributed among the different cities in each group and were not confined to a particular one. The average cost shown is the avei'age

for all the cities in each group.

The cost figures in table 4 are presented

mainly for pm-poses of comparison rather than

as a guide to current costs. They are valuable

in that they show the range of costs of shingles

of different weight, coverage, etc.

VI. METHODS OF APPLICATION '

Figures 1 to 20, inclusive, illustrate methods

of applying asphalt-prepared roll roofings and

shingles, also recommended practices for the

construction of valleys and flashings, and finish- ing hips and ridges. Only the shingles used

most commonly are illustrated. In general,

the purpose has been to show a variety of satis- factory practices rather than to indicate that a

particular method must be used with a particular type of shingle. For example, some illus- trations show a metal drip edge at the eaves, while others use wood shingles for this purpose.

Either is considered satisfactory. Some illus- trations show the use of underlay materials,

and in others they are omitted. The conditions under which underlay materials may be

omitted are indicated in the text.

1. General Discussion

Certain basic principles apply to the application of all types of asphalt-prepared roofings.

These will be considered first, followed by some

of the more important details that should be

followed in the application of particular types

of roofing.

(a) Weather Conditions

Asphalt-prepared roofings are best applied

during clear, mild weather. Extremes of temperature should be avoided whenever possible.

It is a poor practice to walk on asphalt-prepared

roofings at any time, but they should never be

walked on during extremely hot or cold weather.

When the outside temperatui'e is high (90° F

or higher), the asphalt coatings and saturant

will be relatively soft and any pressiu-e on the

roofing may damage it. When the roofing is cold, the coating and saturant are relatively

hard and brittle, so that any sudden bending

may cause cracks. If the outside temperature

is below 60° F, the roofing should be stored in a warm room for 24 hours before application.

Roll roofings should be unrolled slowly and

carefully. Asphalt-prepared roofings, particu-

» The material in this section is taken principally from instructions prepared by manufacturers of asphalt-prepared roofings. These instructions, which are always furnished with the roofings, generally give clear, concise directions, which, if followed, would prevent many of the diffi- culties that are encountered with these materials. Unfortunately, the

instructions are too often disregarded.

[14]
'Direction-of- Prevailing Wind '

SMOOTH or MINERALSURFACED ROLL flOOFING

HORIZONTAL APPLICA TION

OVER- ROOF BOAR.DS

HORIZONTAL SEAMS-LAPPED 2"

VERTICA L SEAMS LAPPED 6"

Figure 1.

WI DE SEL VAG

E

ROLL - ROOFING

HORIZONTAL APPLICATION

O VER. ROOF- BOARDS

(BLIND-NAILING METHOD)

HORIZONTAL SEAMS

LAPPED 19" VERTICAL SEAMS

LAPPED 6"

Figure 2.

286109°—41 3 [15]
Figure 4.

[16]
DIAMOND POINT-

\\ Jlfj R^OLL - R.OOFING

OVEIZ WEATHER-EDA SPHA L T - SHINGL ES -

Figure 5.

PA TTEPNED

R.OLL- R. OOFING

O VER, - WEA THERED - WOOD

SHINGLES

Figure 6.

[171
INDIVIDUAL

SHINGLES

A MER-ICAN METHOD

ALTERNATE COUHSES IN LINE 9"xl2f'

Headlap ab='4§"

Exposure cd= 4

" Spaced ^

UNDERLAY MA TER.IA L . -

15 LB. ASPHALTSATURATEDEELT

OR. SATURATED AND

COA TED BUILDING -PAPER

COVERA GE

DIAGRAM

REPEATING UNIT

INDieA TIONS

1 Ply 4X

2Ply 6 X

3 Ply 73 7,

4 Ply 17 X

Figure 7.

INDI VIDUA L SHINGLES

AMERICAN METHOD

FIRST- AND - FOURTH

COURSES IN LINE

S"xl2^"

Headlap ab -4i'

Exposure cd = 4"

Spaced ^

COVERAGE

DIA GRAM

REPEATING UNIT

INDieA TIONS

2 Ply 14 X

3 Ply 70 7,

4 Ply 16 7

f IS] I

I
/A/D/V/DUAL

S/i/N6LES

WIDE- SPACE METHOD OVER. WOOD SHINGLE5 U51NG STRIPS 3„

Headbp- a5^44

5idelap ef- 17

Tly- exposed- part =4

CO VERA GE

DIAGRAM

[REPEATING UNIT

I NDICATIONS

I ? / P/y 527.

2 Ply 48 X

4 Ply 4 7,

Figure 9.

INDIVIDUAL

SHINGLES

3 FI^ENCH OR

HEXA GONA L METHOD

FOR • REROOFING

16 "y 16

" 2^ Lap

COVERAGE

DIA GRAM

REPEATIN6 UNIT

IN DieA TIONS

\ I Ply 63 X

Ply 28 7, ^m5Ply 9 %

Figure 10.

[19]
INDIVIDUAL

SHINGLES

DUTCH- LAP- METHOD

FOR. RER.OOFING

12 "x 16

" Headlap ab =2

Sidelap ef = ^3

COVERAGE

DIAGRAM

REPEATING-UNIT

INDieA TIONS

I Ply 62 7,

2 Ply 29 7. 3 Ply 97.

Figure 11.

SQUARE -TAB

STRIP SHINGLES

I2j"x 36 "

Headlap- a b =4^

Exposure cd= 4

'

Cutouts =^

COVERAGE

DIAGRAM

REPEATING UNIT

IND/CA TIONS

2Ply 57

^m5Ply 837.

1^4Ply 127

Figure 12.

[20]
SCIUARE-TAB

STRIP- SHINGLES

lO'x 36"

Headlap a b = 2"

Exposurecd= 4

Cutouts = ^" UNDERLAY MATEfllALI5LB. ASPHALTSATURATED- FEWOR. SA TURA TED AND COA TED

BUILDING PAPEIZ

COVERA GE

DIAGRAM

REPEATING UNIT

INDICATIONS

ZJ I Ply J %

m2Ply 50X

mjPly 4lX

Figure 13.

SQUAPE-TAB

STRIP SHINGLES

THICK BUTT TYPE

12 "x 56 " Headlap a-b=2'

Exposure cd^S'

Cutouts

OVER 15 LB. ASPHALT

SA TURA TED FEL T

OR

SA TURA TED AND COA TED

BUILDING - PAPER.

COVERAGE

DIAGRAM

REPEATING UNIT

INDICATIONS

I Ply 4 y. 2Ply 59 X

5 Ply 37 X

Figure 14.

[21]
Figure 15.

Figure 16.

[22]

Figure 19.

[24]
Figure 20.

larly roll roofings, should never be applied at temperatures below 40° F. Asphalt shingles are intentionally made more

rigid than roll roofings and if applied during

cold weather consideration should be given to

this fact. Wlien it is necessary to fold sliingles, as over the ridge of a roof, they may require

warming before they are bent.

Asphalt-prepared roofings should never be

stored outdoors or in any damp place before

application. These roofings are waterproof

when applied properly to a roof, but the nonweather side is usually covered with only an

extremely thin asphalt coating through which

moisture may pass to the saturated felt.

(6) Roof Deck

The importance of a proper roof deck for asphalt-prepared roofings cannot be emphasized too strongly. All types of these roofings

should have a smooth, solid deck in order to render the best service.

New roof decks should be of dry, well-seasoned lumber, because wet or unseasoned

boards shrink and warp on drying and cause

buckles or wrinkles in the roofing. Ample

ventilation of new dwellings should be provided

while plaster is drying, otherwise the roof

boards may swell and buckle.

Roof boards should be not less than % in. thick, of uniform thickness, and not more than

8 in. wide. Tongued-and-grooved boards 6

in. wide are preferable, but square-cut boards

are satisfactory if they are laid close together

and fastened securely. Knot holes in the

sheathing boards should be avoided whenever

possible but, if present, should be covered

with tin. Asphalt-prepared roofings are frequently

applied over old wood shingles and when laid properly, usually give satisfactory results. One of the main objections to this practice is that it is not possible to secure proper nailing

since most wood shingles are laid on so-called

shingle lath that are spaced several inches, so that some of the nails used to fasten the new

roof do not strike the shingle lath. Another

serious objection is that a wood-shingle roof does

not present a smooth surface. This may be

obviated in part by replacing any decayed or missing shingles and nailing down or cutting

off corners of any shingles that are warped.

Beveled wood strips nailed over the old wood

shingles also help to secure a smooth deck.

These strips should be about 4 in. wide, with

the thick side as thick as the butts of the wood

shingles (fig. 9). The best practice, however,

is to remove the wood shmgles, taking care that

[25]
all nails used to fasten them are removed, to clear away any debris, and to fill in the spaces

between the shingle lath with wood strips of

the same thickness as the lath.

(c) Valleys

Valleys are usually constructed of roll roofings, although metal valleys may be used

satisfactorily if provision is made for changes in dimensions with changes of temperature. The

chief advantage of the use of roll roofings for valleys is that the entire roof is covered with

the same type of material, so that dift'erences in the rate of expansion and contraction with

changes of temperature do not exist. When roll roofing is used for valleys, it is used

in double thickness. The first layer should l>e preferably 18 in. wide, and, if it is a mineralsurfaced roof, should be laid with the exposure

side down. The second layer should be the

full width of the roll (36 in.) and should be laid

with the weather side up. Each sheet should

be made to lie smoothly and conform to the

contour of the roof. Valley sheets should be

nailed at intervals of approximately 18 in. to hold them in place until the remainder of the

roofing is applied. (See fig. 17.)

One manufacturer recommends two strips

of roofing for valleys, the first 9 in. wide and the

second 18 in. Another recommends strips

16 and 20 in. wide. The advantage of the

wider strips is obvious.

(d) Edging

Some method of protecting the edges of the

roof deck at the eaves and gable ends is desirable. The method recommended most generally for new roof decks is the application of galvanized-metal strips, painted on both sides. These strips should be at least 3 in. wide, and

should extend % in. beyond the edge of the roof

to form a drip edge (figs. 3, 7, and 12). Another method is to apply strips of roll roofing

at all edges (fig. 1). These strips should ex- tend about 4 in. on the roof proper, and should

be bent over and nailed securely to the edges of

the sheathing and fascia boards and extend

about Yo in. beyond to form a drip edge. Fre- quently a course of wood shingles is applied at the eaves, with the butts of the shingles extending about % in. beyond the sheathing board to form a drip edge (fig. 8). In applying asphalt-prepared roofings, over wood shingles, it is good practice to cut away

the wood shingles at the eaves and gables for a space of 4 in. and install wood strips % in. thick and 4 in. wide. (See fig. 9.)

2. Roll Roofings

This section does not propose to give complete details of the application of roll roofings

and shingles, because, as mentioned previously,

adequate instruction sheets always accompany

shipments of these materials. It is intended

merely to emphasize some of the more important details of installation.

(a) General Instructions

Asphalt-prepared roll roofings are usually

furnished in sheets 36 in. wide. Rolls of smooth-surfaced roofings contain 108 or 216 sq

ft; rolls of mineral-surfaced roofings only 108

sq ft. A small proportion of the rolls may

contain two pieces of roofing, in which case

slightly more than 108 sq ft is furnished in order to provide for the additional lap where the

ends of the two pieces must be joined together.

Nails and lap cement are provided with each

roll of roofing. These are usually placed in the center of the rolls, which are wound tightly and

wrapped with paper. The ends of the rolls are normally closed with caps, which protect the

roofing and prevent the nails and lap cement

from being lost. Metal caps, or other similar fixtures intended

to fasten the seams more securely, are used

frequently, particularly with smooth-surfaced

prepared roofings.

Considerable care should be taken in unroll- ing the rolls of roofing. The wrappings and

caps should be removed and the "trimmings"

(nails and lap cement) taken from the roll. Then, while the roll is standing on end, each

convolution should be loosened by passing the

hand between the layers from one end of the

sheet to the other. The roll should then be

laid flat and unrolled slowly.

Manufacturer's instructions should be fol- lowed as to whether the surface on the inside or

[26]
outside of a roll of smooth-surfaced prepared

roofing should be exposed to the weather.

Mineral-surfaced roofings are always rolled with the exposure surface on the inside of the

roll. A safe practice with both smooth- and

mineral-surfaced roofings is to cut the strips to proper length and lay them on a smooth, flat surface for several hours, or until they lie perfectly flat. Roll roolings are usuallj^ laid horizontally.^"

They naay, however, be laid vertically on slopes

greater than 4 in. per horizontal foot.,

(6) Pitch of the Roof

The reconmiendations of manufacturers concerning the minimum pitch of roofs on which

roll roofings may be laid with safety vary from

"a slight pitch" to 4 in. per horizontal foot. It can be taken as axiomatic that the greater the

pitch the better the service that may be expected

from the roof. A probable safe minimum

pitch for roll roofings laid by the horizontal

method and lapped 2 or 3 in. is 4 in. per horizontal foot; and for roofs laid vertically, 6 in. per horizontal foot.

If it is necessary to use roll roofings on roofs

with lower pitch, the lap should be increased

proportionately. Some manufacturers recom- mend the use of the so-called split-surface or wide-selvage roofings, where but half of the

sheet is surfaced with granules, figure 2, or

regular smooth-surfaced roll roofings lapped

1 in. more than one-half the width of the sheet on very low-pitched roofs.

(c) Horizontal Application

In laying roll roofings horizontally Avith nails

exposed, one should start at the lower edge

with a fuU-length sheet, laying it parallel to the eaves (fig. 1). If a metal edge strip is used,

the lower edge of this sheet should project

about K in. beyond the edging strip. If a strip of roll roofing is used at the edge, that part of the edging strip on the roof proper should be

coated with lap cement, and the first sheet of roofing laid flush with the edge at the eaves and

rake. This sheet should be fastened with nails

The terms "horizontal application" and "vertical application" are used generally in the roofing industry, the former to indicate that the

sheets are laid parallel with the eaves; the latter, that they are laid per- pendicular to the eaves.

spaced about 24 in. apart and 1 in. from the

top of the sheet. The second course should be started by a

half-length sheet, in order to V^reak joints, lapping this sheet 2 in., or more if desired, over

the first, and nailing along the upper edge as described for the fii'st sheet. Laps at the ends

of sheets should be at least 4 in., and, preferably 6 in., wide.

The third course should be started with a

full-length sheet and succeeding courses pro- ceed up the roof, to the ridge, starting alter- nately with full- and half-length sheets. The

top sheets from each side of the roof should

extend at least 3 in. over the ridge and be

nailed securely.

Lap cement should be applied liberally and

continuously to that part of the upper edge of the sheet that will be lapped by the sheet

above. Care should be taken that the sheets

lie perfectly smooth and fiat before the seams

are cemented. The lap cement should be

allowed to become tacky before the seams are

nailed. Horizontal seams must always be

lapped shingle fashion to shed water and vertical seams must be lapped away from pi-evailing winds.

The nails used to fasten the seams should be

% in. long on new roof decks, with heads not

less than in. wide. The nails furnished with

roofings are usually galvanized, those with a heavy coating of zinc being most desnable.

Nails 1% m. long should be used when roll roofing is applied over old wood shmgles.

The nails should be spaced 2 in., from % to

1 in., from the edge of the sheet in long seams, and 1 in. staggered in short vertical seams (end

laps). Care must be taken not to drive nails

in cracks between boards in old roof decks. If cracks are present, it is a good practice to mark their location on the sheets.

(d) Blind Nailing

Roofings laid by the blmd-nailing method,

with no nailheads exposed, are laid as above,

except that the laps must be greater than 2 in. This method is best adapted to smooth-surfaced

roll roofings and the mineral-surfaced roofings

with an unsurfaced selvage at least 3 in. mde.

Each sheet is securely nailed along the top edge

[27]
with nails spaced 2 in. apart and in the center

of the part to be lapped. If a lap wider than

3 in. is employed, the nails should be staggered.

Seams laid by the blind-nailing method should

be weighted down until the lap cement has set thoroughly. Bricks, bags of sand, or weighted

planks may be used for this purpose.

Wide-selvage roofings, as illustrated in fig- ure 2, are always laid by the blind-nailing

method. The wide laps may be cemented with

cements applied cold that are prepared specifically for this purpose, or a mopping of hot

asphalt, similar to that used in the construction

of built-up roofing, may be employed. The

selvage should be fastened with two courses of

nails, the first about 2 in. and the second about

9 in. from the surfaced edge of the sheet. The

nails should be spaced about 8 in. and the two

courses should be staggered. If cold-application cement is used, the laps should be rolled with a heavy roller to insure a smooth surface

and a satisfactory bond between the sheets.

(e) Vertical Application

In general, the directions for horizontal application apply to vertical application of roll roofings, except that the sheets are started from

the ridge, where they are temporarily fastened

with 3 or 4 nails, and unrolled toward the eaves

(fig. 3). The sheets should be allowed to hang

free until they lie smoothly before the laps are cemented and nailed.

Vertical application of roll roofings is usually

considered less desirable than horizontal application, because water must run along the laps

instead of over them. Over old wood shingles,

manufacturers seldom recommend vertical

application of roll roofings because of the diffi- culties of securing proper nailing and smooth

application. However, a system of vertical

application over old wood shingles has proved

quite satisfactory in some localities. With this system, wood strips, as illustrated in figm^e 4, are nailed vertically to the roof through the

wood shingles and thus provide a proper, solid

base for nailing the roofing seams. The seams

are elevated above the remainder of the roof

by the thickness of the beveled strips, so that

water tends to drain away from them. The

fact that the seams are raised slightly relieves

the monotonous appearance of the usual roll- roofing roof.

(J) Hips and Ridges

Hips and ridges may be finished with a strip of roll roofing not less than 18 in. wide, bent

over and fastened on each side and nailed as described for long seams; or they may be

finished with individual asphalt shingles, as illustrated in figure 17. Some manufacturers

recommend a double thickness of roofing at hips and ridges, in which case the first strip

needs to be nailed only at intervals of about

18 in.

ig) Flashings

Flashings at chimneys, vent pipes, and

against vertical walls of dormers are of extreme

importance. Figures 18 and 19 illustrate a

satisfactory method of installing chimney

flashings, using roll roofing except for the

metal counterflashing. Pieces of roll roofing

4 in. square should be cut and fitted as shown

in figure 18 {A). The roll roofing is then laid

in the usual mamier, cementing the tm-ned-up

edges against the chimney as in figure 18 {B).

Strips of roofing 12 in. wide are then cut for each side of the chimney, making each strip

about 12 in. longer than the side to be fiashed.

The strips should be cut and folded as indicated

in figure 19 (C). These strips should be place/i

around the four sides of the chimney and

should be cemented thoroughly to the chimney

and to the roofing underneath. The flashing

should be fastened at the top with a metal

counterflashing and to the roof with nails spaced 2 in., and % in. from the edge (fig. 19, D).

Against vertical brick walls, the roofing

should be turned up about 4 in. and cemented

and nailed to the wall, placing the nails about

8 in. apart. A strip of roofing 12 in. wide, bent

in the center lengthwise, should be fitted into

the angle and cemented thoroughly to the wall

and the roof. It may be fastened to the wall

by means of a wooden strip, either half-round

or beveled, which is nailed securely and the

upper edge puttied with plastic cement so that

the joint is sealed and the water drains away

from the edge. A metal counterflashing is preferable to the wooden strip and should be

used whenever possible. It may be of copper,

[28]
galvanized iron, or terne plate set into the

wall and extending at least 6 in. down over

the flashing strip. If galvanized iron or terne

plate is used, it should be well painted on both

sides. Against dormers covered with asphalt shingles or wood siding, the roll roofing and the

12-in. strip should extend up under the siding

material.

3. Asphalt Shingles

Asphalt shingles are usually marketed in

packages, weighing from 40 to 100 lb. each.

Two to four packages are required to cover one

square of roof, depending on the design of the

shingles.

(a) Pitch of the Roof

The class C label of the Underwriters' Laboratories, Inc. is applicable to asphalt shingles

only when they are laid on inclines exceeding

4 in. to the horizontal foot. Manufacturers recommendations vary considerably in respect to the minimum pitch of asphalt shingle roofs, although the majority advise not less than 4 in. per horizontal foot. One

manufacturer states that 5 in. per horizontal

foot is the minimum for shingles; another that

they are not guaranteed if applied on slopes less than 3 in. to the foot; another that if they are applied on slopes less than 4 in. to the foot, the

roof deck should first be covered with smoothsurfaced asphalt-prepared roofing; another that

4 in. per foot is the minimum for most shingles

but that hexagonal-pattern strip shingles less than 14-in. long should not be laid on inclines

of less than 6 in. to the horizontal foot. The importance of having sufficient slope to the roof deck is greater with asphalt shingles

than with roll roofings, because the latter, when

laid properly, provide a continuous sheet over

the entire roof. Asphalt shingles, while fur- nishing, in many cases, two or three layers of

fabric over the greater part of the roof area, are not continuous, and so have to be designed

and applied properly in order to prevent leaks. For this reason 5 in. per horizontal foot is recom- mended as the minimum pitch for asphaltshingle roofs. Numerous observations have

shown that the waterproofness and weather

resistance of asphalt-shingle roofs increase as

the pitch of the roof is increased. Poi-cli roofs are excepted because they are usually lower

pitched than the main-roof sections.

(b) Underlay

If asphalt shingles are applied to new roof

decks, manufacturers are practically unanimous

in recommending some type of covering for the

roof deck before the shingles are laid. The

materials recommended most generally are

15-lb asphalt-saturated felt or asphalt-saturated

and coated building paper. Reasons given for the use of underlay materials are: increased

waterproofness and heat insulation, protection

for the sheathing boaixls before the shingles are applied, and increased life of the shingles.

Whether or not an underlay material is neces- sary from the standpoint of waterproofness is dependent mainly on the type of shingle and

the pitch of the roof. Shingles that furnish

triple coverage over the greater part of the roof

deck and have an ample headlap (4 in. or greater) need no imdeilay material to make

them waterproof when they are laid on inclines

of 5 in. per foot or more. The underlay material may also be omitted on inclines of 7 or more inches per foot, provided that the weight

of the shingles is not less than 210 lb per square. Light-weight prepared roofings or coated

waterproofing papers are probably more satis- factory for this purpose than asphalt- saturated

felt, since the latter will usually absorb considerable moisture.

The actual heat-insulation value of felts and

papers used as underlay materials, compared

with that of materials that are marketed regularly for insulation purposes, is so small as to be almost negligible. They act as a moisture

barrier to prevent possible condensation on the

under surface of shingles and serve to prevent

air infiltration and heat losses through cracks

in sheathing boards.

(c) Edging and Starting Strips

The edges of the roof deck at gables and eaves should be protected by some sort of edgingstrip extending slightly beyond the edges of the

boaixls to form a drip edge. This is particularly true at the eaves, where the boards will soon rot unless water is prevented from coining in

[29]
contact with them. A galvanized-inetal strip

painted on both sides, projecting % to % in. beyond the edge, and extending about 4 in. on

the main section of the roof, as illustrated in figures 3, 7, and 12, is usually recommended.

A course of wood shingles laid close together

with the butts extending about % in. beyond

the edge of the sheathing boards may be used

satisfactorily at the eaves (see fig. 8). At the eaves it is customary to lay a strip of

roll roofing flush with the edging strip. Some

manufacturexs recommend 12-in. strips, others

18-in. Figures 7, 8, 10, 12, 13, 14, and 16 illus- trate an 18-in. starting strip, but a ftdl 36-in.

strip is most desirable, particiilarly where the eaves project beyond the walls a considerable

distance. This strip should be nailed aboiit 2

in. above the edging strip at such intervals that

the nails will not be exposed when the first course of shingles is laid. It should not extend

over any valley strips. Where there is much

snowfall, a good plan is to use a metal eaves

strip that extends about 36 in. over the main

roof section.

Frequently a course of strip shingles, reversed,

is laid in place of the strip of roll roofing, as in figure 15, or a course of individual shingles, laid

close together, is used (figs. 9 and 11).

(d) Nails and Clips

Galvanized nails, with heads not less than %

in. in diameter and with barbed or plain shaidvs,

11 or 12 gage, are usually recommended for asphalt shingles. Recommendations concerning the length of nails that should be used vary

with difi'erent manufacturers. Table 5 lists nails that may be used safely with the different

kinds of shingles for various conditions of application.

Table 5.

Nails used for asphalt shingles

Roof deck Standard- weight

Giant- weight Thick-butt

in. in. in. New 1 to m 1 to IH VA to IH

Weathered-roll roofings . V/i to IK' 1!4 to IH VA to m Weathered-asphalt .shingles 11/2 to IH V/2 to m VA to 1%

Weathered-wood shingles. _ m m m

The clips that are used for fastening the butts

of shingles, and the corners of shingles laid by

the Dutch-lap method, are usually patented

features, requiring a special tool for installing

them. No attempt will be made to describe

them here. They usually accomplish the

purpose for which they are intended—namely,

that of preventing the shingles from being raised

by high winds. Most clips penetrate the

exposed portion of the shingle and thus furnish

a means for water to reach the felt base of the

shingle at the point the clip penetrates.

(e) Hips and Ridges

Hips and ridges are best finished with in- dividual sliingles although strips of roll roofing

or metal ridge rolls may be used. In finishing

hips with individual shingles, it is desirable to

first lay a double layer of asphalt-satiu-ated

felt 6 in. wide, as shown in figure 17. The

shingles are then applied in the same manner

as on the roof, starting at the lowest point and

bending the shingle equally across the hip.

One nail is placed on each side, about % in . from

the edge. The shingles used to finish the hips

should be kept in line with the courses of the

main roof, exposing standard-weight shingles

4 in. and heavy-weight shingles 5 in. (See

fig. 17.)

Ridges are finished in the same manner as

hips, always starting from the direction opposite that of the prevailing winds (fig. 17).

Shingles for finishing hips and ridges may be

cut from strip shingles by trimming each

shingle to the edge of the cut-out section, if individual shingles are not available.

(/) Flashings

Chimney flashings may be constructed as illustrated for roll roofings, figures 18 and 19,

except that the flashing strips should be

installed before the shingles are laid, so that

the strips will extend underneath the shingles

except at the bottom of the slope. Metal

flashings and counterflashings, as shown in figure 17, are preferable to those made from

roll roofings.

Figure 20 (A) shows a method of installing

flashings around the vertical walls of a dormer,

using an 18-inch strip of roll roofing bent so that the section underneath the asphalt shingles

is 12 in. wide. Figui'e 20 {B) shows the completed dormer.

[30]
((/) Methods oj Applying] Particular Types oj

Shingles

As stated previously, no attempt will be

made to describe exact methods for applying

all types of shingles, as these are covered

adequately by the instructions issued by the

manufacturers. However, some of the more

important details are summarized here.

(1) Individual shingles—American Method.

In laying individual shingles by the American

method, as illustrated in figures 7 and 8, standard-weight shingles are usually spaced

)i in. and heavy-weight shingles % in. The

spaces between shingles in successive courses may be staggered one-half (fig. 7) or one-third

(fig. 8) the width of a shingle. For the former

method, the fu'st course is started with a full- width shingle, the second with a half-width

shingle, the third with a full-width, etc. For

the latter, the first course is started with a

full-width shingle, the second with two-thirds

of a shingle, the third with one-third of a

shingle, the fourth with a full-width shingle, etc. The latter method provides the better coverage.

A safe rule to follow is to expose standardweight shingles not more than 4 in. and heavyweight shingles not more than 5 in. Nails are placed as indicated in figures 7 and 8.

(2) Individual Shingles—Wide-Space, Hexagonal, and Dutch-Lap Methods.—The widespace, hexagonal, and Dutch-lap methods of applying individual shingles (figs. 9, 10, and 11)

should not be employed except for reroofing over weathered-wood shingles or asphaltprepared roll roofings and shingles. The greater

the headlap and sidelap obtained with shingles

applied by these methods, the more waterproof

will be the roof ; but they should not be used on

roofs of low pitch nor in regions subject to driving rains.

(S) Square-butt strip shingles.

Shingles may be laid so that each cut-out

section falls in the center of the tab of a shingle

in the next course above, or with the cut-out

section one-third of the width of a tab from

the cut-out section of a shingle in the course

above. Figures 12 and 13 show the effect of

shingles laid by the first method; shingles laid by the second method would appear as illustrated in figure 8. The first nietliod is obtained

by starting the first course with a full-width

shingle, the second with a half-width shingle,

the third with a full-width, etc., or by starting

the first course with a full-width shingle, the

second with a shingle from which one-half tab

has been cut, the third with a shingle from

which one tab has been cut, the fourth with one from which Iji tabs have been cut, etc. To obtain the second effect, the first course is started with a full shingle, the second with one from which one-third of a tab has been cut, the third with one from which two-thirds of a tab has been cut, the fourth with one from

which a full tab has been cut or with a full- width shingle, the fifth as the second, etc. Strip shingles are applied so that the ends

barely touch each other. They should not be

spaced and the ends should not be forced

together.

With regard to exposure, the same rule holds

for strip shingles as for individual ones—that

is, standard-weight shingles are exposed not more than 4 in., heavy-weight and thick-butt

shingles not more than 5 in. The length of the cut-out section of a shingle determines the

distance of exposure. The ends of the tabs

should extend exactly to the tops of the cut-out

sections of the shingles in the course next below.

The nails are placed as shown in figures 12,

13, and 14 for normal conditions of exposure.

For severe conditions, such as prevailing high

winds, driving rains, etc., the shingles will be

fastened more securely if the nails are placed as

illustrated in figure 15. The extra layer of asphalt and the granules on thick-butt shingles

usually extend a short distance above the cut- out sections. The nails should always be

placed in the thicker portion of these shingles,

which otherwise might suffer damage from

winds.

In order to secure smooth application of

strip shingles of all types, the nails at the center should be placed first, and then those at the ends; or the nailing may proceed from one end of a shingle to the other. Strip shingles

should never be nailed first at the ends and

then at the center.

(4) Hexagonal-pattern strip shingles.

The fii'st course is started with a fuU-width

[31]
shingle, the second with a shingle from which

one-half tab has been cut, the third with a full- width shingle, the fourth as the second, and so on, alternately.

Hexagonal-pattern strip shingles are more

vulnerable to driving rains than square-tab

shingles. They should always be laid with an

underlay material, and should never be applied

to roofs of slight pitch.

The distance of exposure of these shingles is also determined by the length of the tabs. The

ends of the tabs are laid flush with the tops of

the cut-out sections of the shingles in the next

course below.

The nails are placed as illustrated in figure 16.

VII. WEATHERING OF ASPHALT-PREPARED ROOFINGS

The weathering of asphalt-prepared roofings

is discussed in considerable detail in Building

Materials and Structures Reports BMS6 and

BMS29. (See footnote, page 2.) These re- ports also present numerous illustrations of

weathered roofings after varying periods of ex- posure in the Southeastern and Northeastern

States. It is apparent from these studies, and

from similar studies in other sections of the

country, that it is not possible to ascribe a defi- nite "life" to any particular type of asphaltprepared roofing. With these, as with other

roofings, many factors other than the actual

materials used must be considered in studying

durability. The workmanship used in applying

a roof is as important as the quality of the

material, because a roof poorly constructed of good or poor materials will never render satis- factory service.

Sunlight, oxygen, moisture, and heat are the

principal factors that cause organic materials to deteriorate."

This explains why asphalt-prepared roofings

weather more rapidly in warm, humid climates

where there is much sunshine, than in cooler,

dry climates with less sunshine. Asphalt-prepared roofings exposed in the Northeastern

States may be expected to give from 50 to 100

percent longer service than the same materials

exposed similarly in the Southeastern States.

II O. Q. Strieter and H. R. Snoke, J. Research NBS 16, 481 (1936) RP886.

The foregoing also explains why the southern

exposvn-e of a roof, exposed to long periods of sunlight, invariably shows more rapid weathering than the northern exposure; and why mineral-surfaced roofings, with the asphalt coating

protected from the sunlight, weather less rapidly than the smooth-surfaced varieties. Asphalt-prepared roofings weather more

rapidly on roofs of low than on roofs of steep

pitch. The roofs of porches, which are usually

less steep than the main-roof sections, generally

show more severe weathering than the main

roof. Apparently this is because the flatter slopes are subjected to more severe moisture

conditions.

In general, roofings that provide the best

coverage resist weathering best. The oldest

asphalt shingles in any location are invariably

individual shingles laid by the American method.

VIII. MAINTENANCE OF ASPHALTPREPARED ROOFINGS

1. Smooth-Surfaced Roofings

Smooth-surfaced, asphalt-prepared roll roof- ings should be recoated regularly to render the

best service. The asphalt coating on these

roofings, being exposed directly to the sunlight,

deteriorates rather rapidly and, unless renewed,

will permit water to enter the felt base and

hasten failure. Numerous coating materials are available at a wide range of prices. They are usuaUy

described as "Asphalt Fibrous Roof Coatings"

and are composed normally of an asphaltic base,

with or without fatty (drying) oils, thinned to heavy-brushing consistency with a volatile

thinner, and containing mineral filler, usually

asbestos fibers. Coal-tar and vegetable-gum

(cottonseed-oil pitch) base coatings are also available. Most brush coatings are intended

for application at the rate of 1 gallon to approximately 50 sq ft of roof surface. Two systems for recoating asphalt-prepared

roofings have been developed recently. In both

of these the roofing is first coated with an asphaltic coating into which mineral granules are embedded. They have been available for only a short time, so that no definite recommendations can be made concerning them.

[32]
If recoated regularly, smooth-surfaced roofings

may last as long or longer than the mineralsurfaced varieties. The frequency of recoating

that is necessary will determine which type is the more economical.

No definite recommendation can be made

concerning the frequency of the recoating operation, for this will vary with the difl'erent weights of roofings and in dift'erent locations.

It is reasonably certain, however, that recoating

will be advisable after 5 years of exposure, if not earlier. The heavier, thicker grades of roofing will normally resist weathering better

than the lighter grades. There is probably

greater variation in the behavior to weathering

of roofings of this class than in any other put

out by different manufacturers.

Particular attention should be paid to the seams of roll roofings that have stood for several

years. Any seams that have opened should be

recemented; loose nails should be pulled, the

holes sealed with flashing cement, and new nails

inserted where necessary.

2. Mineral-Surfaced Roofings

Recoating of mineral-surfaced roll roofings

is not recommended unless they have weathered

badly. The mineral granules protect the as- phalt coating from the sunlight, so that nor- mally these roofings should resist weathering

for relatively long periods. If coatings are

applied to roofings that still retain their granules, the thinner in the coating material may

soften the asphalt coating so that it will not

retain the granules.

The seams of mineral-surfaced roll roofings

should be maintained with the same care as

those of smooth-surfaced roofings—that is, they should be inspected regularly and re- cemented where they have opened. Loose

nails should be pulled, the nail holes sealed with

flashing cement, and new nails inserted where

necessary. The recoating of weathered asphalt shingles

with coating materials of the type recommended

for smooth-surfaced prepared roofings is not

considered good practice. Cases have been

observed frequently where the number of leaks

in a roof has been multiplied greatly by the

application of a roof coating. This happens

most frequently on i-elatively low-pitched roofs

covered with shingles that provide a small

headlap. The leaks are apparently caused by

failure to seal down the edges of the tabs completely. During driving rains water may be

driven under the tabs, which, being sealed

partially, will cause it to back up over the top

of the shingle underneath. Also, careless application of the coating may form miniature

dams at the cut-out sections of shingles.

The systems mentioned under smooth-surfaced roofings, in which mineral granules are embedded in an asphaltic coating, are recom- mended by those who developed them as suitable for mineral-surfaced roll roofings and

shingles.

Shingles that are weathered badly frequently

warp or curl after being recoated. Apparently

this is caused by the partial absorption of the

coating by the shingle, which, not being ce- mented to the shingle underneath, is distorted

when the coating dries. Roofs of badly warped

shingles are particularly vulnerable to driving

rains.

The author expresses appreciation to G. W.

Shaw, of the Building Practices and Specifications Section of the Bureau, who made the

drawings published in this report. Acknowledgment is also made to J. S. Bryant, Managing Director, Asphalt Roofing Industry Bureau, for copies of instructions for the application of asphalt-prepared roofings issued by

manufacturers; and to C. N. Forrest, Chairman, Research Committee, Asphalt Roofing

Industry Bureau, for reviewing the report.

Valuable assistance was also given by 0. G.

Stricter, Research Associate at the National

Bureau of Standards for the Asphalt Roofing

Industry Bureau, and L. J. Waldron, L. R.

Kleinschmidt, and E. J. Schell, of the staft' of

the National Bureau of Standards.

IX. SPECIFICATIONS

Federal Specifications: ^~ SS-R-501, Roofing, Asphalt- Prepared, Smooth-Surfaced SS-R-511, Roofing; Asphalt and Asbestos-Prepared,

Mineral-Surfaced

12 Obtainable from the Superintendent of Documents. Government

Printing OflBce, Washington, D. C, price 5 cents each, stamps not

accepted.

33]
SS-R-521, Roofing and Shingles; Asphalt- Prepared,

Mineral-Surfaced

Specifications of the Underwriters' Laboratories, Inc.: Standard for Class C Asphalt Rag-Felt Sheet Roofing

and Shingles. List of Inspected Fire Protection Equipment and

Materials.

Specifications of the American Society for Testing

Materials: " D2'24-37T, Tentative Specifications for Asphalt

Roofing Surfaced with Powdered Talc

or Mica

13 Obtainable from the Underwriters' Laboratories, Inc., 207 E. Ohio

St., Chicago, 111^

1* Obtainable from the American Society for Testing Materials, 260

S. Broad St., Philadelphia, Pa. For single copies and lots up to 9, 25 cents per copy; lots of 10 to 24, 20 cents per copy; and lots of 25 to 99, 17i,4 cents per copy.

D225-37T, Tentative Specifications for Asphalt

Shingles Surfaced with Coarse Mineral

Granules

D248-37T, Tentative Specifications for Asphalt

Roofing Surfaced With Fine Mineral

Granules

D249-37T, Tentative Specifications for A.sphalt

Roofing Surfaced with Coarse Mineral

Granules

D371-37T, Tentative Specifications for Asphalt

Cap Sheet Surfaced with Coarse Mineral Granules.

Washington, June 11, 1940.

o
BUILDING MATERIALS AND STRUCTURES REPORTS

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The following publications in this series are available by purchase from the Superintendent of Documents at the prices indicated:

BMSl Research on Building Materials and Structures for Use in Low-Cost Housing 10?^ BMS2 Methods of Determining the Structural Properties of Low-Cost House Constructions 10^ BMS3 Suitability of Fiber Insulating Lath as a Plaster Base 10^ BMS4 Accelerated Aging of Fiber Building Boards 10$^ BMS5 Structural Properties of Six Masonry Wall Constructions 155^ BMS6 Survey of Roofing Materials in the Southeastern States 15^ BMS7 Water Permeability of Masonry Walls 10^5 BMS8 Methods of Investigation of Surface Treatment for Corrosion Protection of Steel 10^5 BMS9 Structural Properties of the Insulated Steel Construction Co.'s "Frameless-Steel" Constructions for Walls, Partitions, Floors, and Roofs 10^ BMSIO Structural Properties of One of the "Keystone Beam Steel Floor" Constructions Sponsored by the H. H. Robertson Co 10^ BMSll Structural Properties of the Curren Fabrihome Corporation's "Fabrihome" Constructions for Walls and Partitions 10^ BMS12 Structural Properties of "Steelox" Constructions for Walls, Partitions, Floors, and Roofs

Sponsored by Steel Buildings, Inc Ib^ BMS13 Properties of Some Fiber Building Boards of Current Manufacture 10^ BMS14 Indentation and Recovery of Low-Cost Floor Coverings 10^ BMS15 Structural Properties of "Wheeling Long-Span Steel Floor" Construction Sponsored by

Wheeling Corrugating Co 10^ BMS16 Structural Properties of a "Tilecrete" Floor Construction Sponsored by Tilecrete

Floors, Inc 10(5 BMS17 Sound Insulation of Wall and Floor Constructions 10^ BMS18 Structural Properties of "Pre-Fab" Constructions for Walls, Partitions, and Floors Sponsored by the Harnischfeger Corporation 10^ BMS19 Preparation and Revision of Building Codes 15f5 BMS20 Structural Properties of "Twachtman" Constructions for Walls and Floors Sponsored by

Connecticut Pre-Cast Buildings Corporation 10^ BMS21 Structural Properties of a Concrete-Block Cavity-Wall Construction Sponsored by the National Concrete Masonry Association 10^ BMS22 Structural Properties of "Dun-Ti-Stone" Wall Construction Sponsored by the W. E. Dunn Manufacturing Co 10^ BMS23 Structural Properties of a Brick Cavity-Wall Construction Sponsored by the Brick

Manufacturers Association of New York, Inc 10(5 BMS24 Structural Properties of a Reinforced-Brick Wall Construction and a Brick-Tile CavityWall Construction Sponsored by the Structural Clay Products Institute 10^5 BMS25 Structural Properties of Conventional Wood-Frame Constructions for Walls, Partitions,

Floors, and Roofs 15(5 BMS26 Structural Properties of "Nelson Pre-Cast Concrete Foundation" Wall Construction

Sponsored by the Nelson Cement Stone Co., Inc 10(5 BMS27 Structural Properties of "Bender Steel Home" Wall Construction Sponsored by The

Bender Body Co 10(5 BMS28 Backflow Prevention in Over-Rim Water Supplies 10(5

[List continued on cover page iv]
BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page iii] BMS29 Survey of Roofing Materials in tlie Northeastern States 10(i BMS30 Structural Properties of a Wood-Frame Wall Construction Sponsored by the Douglas

Fir Plywood Association lOji BMS31 Structural Properties of "Insulite" Wall and "Insulite" Partition Constructions Sponsored by The Insulite Co 15jt BMS32 Structural Properties of Two Brick-Concrete-Block Wall Constructions and a Concrete- Block WaU Construction Sponsored by the National Concrete Masonry Association. 10^ BMS33 Plastic Calking Materials 10^ BMS34 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 1 10^ BMS35 Stability of Sheathing Papers as Determined by Accelerated Aging 10^ BMS36 Structural Properties of Wood-Frame Wall, Partition, Floor, and Roof Constructions

with "Red Stripe" Lath Sponsored by the Western Paper and Manufacturing Co lOji BMS37 Structural Properties of "Palisade Homes" Constructions for Walls, Partitions, and

Floors, Sponsored by Palisade Homes lOji BMS38 Structural Properties of Two "Dunstone" Wall Constructions Sponsored by the W. E. Dunn Manufacturing Co 10^ BMS39 Structural Properties of a Wall Construction of "Pfeifer Units" Sponsored by the Wisconsin Units Co 10^ BMS40 Structural Properties of a Wall Construction of "Knap Concrete WaU Units" Sponsored

by Knap America, Inc 10^ BMS41 Effect of Heating and Cooling on the Permeability of Masonry Walls 10^ BMS42 Structural Properties of Wood-Frame Wall and Partition Constructions with "Celotex"

Insulating Boards Sponsored by the Celotex Corporation lOfS BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 10^ BMS44 Surface Treatment of Steel Prior to Painting 10^ BMS45 Air Infiltration Through Windows 10^ BMS46 Structural Properties of "Scot-Bilt" Prefabricated Sheet-Steel Constructions for Walls,

Floors, and Roofs Sponsored by the Globe-Wernicke Co 10^ BMS47 Structural Properties of Prefabricated Wood-Frame Constructions for Walls, Partitions, and Floors Sponsored by American Houses, Inc 100 BMS48 Structural Properties of "Precision-Built" Frame WaU and Partition Constructions

Sponsored by the Homasote Co 100 BMS49 Metallic Roofing for Low-Cost House Construction 100 BMS50 Stability of Fiber Building {Boards as Determined by Accelerated Aging 100 BMS51 Structural Properties of "Tilecrete Type A" Floor Construction Sponsored by the

Tilecrete Corporation 100 BMS52 Effect of Ceiling Insulation on Summer Comfort 100 BMS53 Structural Properties of a Masonry Wall Construction of "Munlock Dry Wall Brick"

Sponsored by the Munlock Engineering Co 100 BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler 100 BMS55 Effect of Wetting and Drying on the Permeability of Masonry WaUs 100 BMS56 A Survey of Humidities in Residences 100 BMS57 Roofing in the United States—Results of a Questionnaire 100 BMS58 Strength of Soft-Soldered Joints in Copper Tubing 100 BMS59 Properties of Adhesives for Floor Coverings 100 BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 150 BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete WaU Constructions 100 BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by the Portland Cement Association 100 BMS63 Moisture Condensation in Building Walls 100 BMS64 Solar Heating of Various Surfaces 100 BMS65 Methods of Estimating Loads in Plumbing Systems 100 BMS66 Plumbing Manual 200 BMS68 Performance Test of Floor Coverings for Use in Low-Cost Housing. Part 3 150 BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging 100 BMS70 Asphalt-Prepared Roll Roofings and Shingles 150