NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

421.04-Z0-421Z248 Z3 May 1966 9304

ROOFING RESEARCH

by

Thomas H. Boone

NOT FOR PUBLICATION

Presented at the

Annual Meeting

of the

Society of American Military Engineers

Sponsored by

National Bureau of Standards

IMPORTANT NOTICE NATIONAL BUREAU OF ST

for use within the Government, and review. For this reason, th whole or in part, is not authoi Bureau of Standards, Washingt

the Report has been specifically

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

ss accounting documents intended

subjected to additional evaluation

listing of this Report, either in

e Office of the Director, National

the Government agency for which

opies for its own use.

U. S. DEPARTMENT OF COMMERCE.

NATIONAL OUREAU OF STANDARDS

ROOFING RESEARCH

by

Thomas H. Boone

1. SUMMARY

Studies of the engineering properties of built-up roofing have been underway in the Building Research Laboratories of NBS. Utilization of these properties will be discussed in relation to the reduction of potential failures of

roofing membranes in service.

Descriptions of the newly-developed fluid roofing systems and the one-ply

sheet systems which have both been brought into play by the increasing use of

irregular- shaped thin- shell concrete decks, increased cost of labor, and the

demand for more factory-finished products that leave little room for application errors, will also be given.

References to research by others particularly significant to improved

roofing systems will be cited.

2 . INTRODUCTION

Considerable progress has been made in the development and design of

different types of roofing systems. I would like to present to you three

facets of roofing research and developments:

FIRST some highlights of roofing research in the Building Research

Division at the National Bureau of Standards;

SECOND a brief description of some of the newly- developed roofing systems;

and,

THIRD the present status of roofing research.
-l3. ROOFING RESEARCH AT NBS

A major percentage of flat roof construction in the United States consists of built-up roof systems. The term "Built-Up Roofing" is used to describe

roofs which are installed in layers directly upon the roof decks of buildings.

There are many different materials and, they are placed over many different

types of insulated or non- insulated roof decks. In recent years serious

splitting and wrinkle-cracking failures have occurred in built-up roof membranes. These failures appeared most frequently on membranes applied over

insulation and after periods of cold weather.

A part of the roofing research at the National Bureau of Standards has

been to measure the natural solar heating and radiative cooling of exposed

built-up roof systems and to obtain data on the thermal expansion and contraction characteristics of the composite built-up membrane in order to better

understand causes of the splitting failures.

Ten built-up roofs on wood and concrete decks, both insulated and noninsulated were constructed and placed on top of a roof in Washington, D. C.

Each construction contained copper-constantan thermocuples at selected

locations for recording temperature continously Ik hours a day. Figure 1

is a schematic diagram of a typical specimen. Five surfaces representing those

commonly used on built-up roofs were used in the experimental work. Figure 2

shows a general view of the outdoor exposures.
-3-

The results illustrated in Figure 3 show the extent of temperature changes

for a smooth black surface built-up membrane on insulated and uninsulated concrete decks on a summer day in August. Figure 4 illustrates the effect of the

protective surface on the temperature and the rate of temperature change of

membranes placed over insulation. From this series of experiments sub-cooling temperature less than ambient were also measured! 1]—^

These temperature variations expose the roofing to extreme thermal

stresses particularly in the range from 30°F to -30°F. Both the data obtained

and observations of splitting and shrinkage suggest that thermal movement of

the built-up roofing may be involved. Figure 5 illustrates the method used

to measure the membrane movements with a Whittemore Strain Guage. The results

shown in Tables 1 and I indicate built-up roof membranes undergo greater

thermal expansive and contractive movements than most other components of a

roof system at low temperatures.

From these investigations [2] the following suggestions have been made,

and accepted by some roofing contractors and manufacturers to help prevent

premature roofing failure:

1. Tape insulation joints

1. Place long dimension of insulation parallel to short dimension

of roof.

3. Place long dimension of roofing felt parallel to long dimension

of roof.

1 /

Figures in brackets indicate literature references at the end of this paper.
-3 aTABLE 1. APPARENT LINEAR THERMAL EXPANSION COEFFICIENT OF ROOFING FELTS

(TEMPERATURE RANGE 30 °F to -SO^F)

Description

Felt, Organic, Asphalt-Saturated

Felt, Asbestos, Asphalt-Saturated

Felt, Glass fiber, Asphalt-Saturated

Felt, Organic, Coal-tar Saturated

Expansion Coefficient per °F

"With Machine*' "Across Machine"

6.3 X 10"^ 13.3 X

10“^

6 .X 10"^ 13.0 X 10-6

14.5 X 10-6 18.2 X 10-6

6.5 X 10"^ 15.2 X 10"6

TABLE 2. APPARENT LINEAR THERMAL EXPANSION COEFFICIENT OF

BUILT-UP MEMBRANES (TEMPERATURE RANGE 30 °F to -30 °F)

Description

Asphalt - Asphalt-Sat. Organic Felt

Asphalt - Asphalt-Sat. Asbestos Felt

Asphalt - Asphalt-Sat. Glass Felt

Coal-Tar Pitch-Coal-Tar-Sat. Organic Felt

Expansion Coefficient per °F

"With Machine" "Across Machine"

10.9 X

10"^ 20.8 X 10

8.3 X 10"6 20.3 X 10

18.1 X

10"^ 26.1 X 10

10.4 X 10"^ 29.4 X 10
-4-

4. Have positive adhesion of insulation to deck.

5. Have optimum strength adhesive of roof membrant to insulation.

6. Use of expansion joints.

7. In areas of the country were extreme cold weather prevails

use roofing memoranes with high thermal- shock resistance.

4. NEW ROOFING SYSTEMS

A number of new roofing materials and roof systems have appeared on the

market in the last 5 years. Some of these systems have been introduced as

substitutes for current types of roofing for both flat and steep roofs, whereas, others have been promoted to serve a particular function which conventional

roofings can accomplish only with difficulty; for example, the protection .f

roofs of unusual contours as the curved shells, the dome, the folded plate, or

the hyperbolic paraboloid as shown in Figures 6 and 7. In some cases, the new

systems were designed to fulfill both needs. A few of the newer systems allow

more utilization of the roof as a work or recreation area.

Studies of the outdoor exposure effects and simulated exposure effects are

being made on the roofs. The two types being evaluated are prefabricated

sheets and liquid- applied coatings. The sheet materials have an exposed top

surface of chloroprene (Neoprene) rubber, chlorosulfonated polyethylene

(Hypalon) rubber, butyl-rubber or polyvinyl- fluoride (Tedlar) polymer. The back

layer of some of the sheets are asbestos felts. The sheets are applied with an

organic solvent-based adhesive with the overlapped joints tapped.
-5-

The liquid-applied coatings are brushed, rolled, or sprayed in multi

layers. In one recommended commercial system six coatings, 1-primer, 3-base

and 2-top coatings, are applied to yield a total dry film thickness of over

20 mils. The liquid-applied coatings under study for their durability are

noprene-Hypalon , butyl-rubber emulsion without top coating and with a top

coating of Hypalon or polyvinyl chloride acetate, silicone rubber and polyurethane foam. Fiber reinforcement of glass fiber cloth, glass fiber random

nat, or chopped glass fibers are used.

Surface preparation plays a very important part in the success or

failure of these new systems. The surfaces for the most part must be clean,

dry, and primed because of the need for mechanical and chemical bond to the

deck being waterproofed or roofed.

5. ROOFING RESEARCH BY OTHERS

With the introduction of rubbers and plastics into this area of building

construction large chemical companies have joined the roofing products

manufacturers in studying the properties of roofing.

Studies on wind resistance, nailing and hail damage have been undertaken

by the Underwriters' Laboratories and many roofing manufacturers.

Moisture effects are being studied at the Pennyslvania State University.

Load-strain properties and their relation to splitting are being measured

by the Governmental Building Research organizations in Canada and in Australia.

Development of a thermal- shock resistance factor for bituminous built-up

roofing membrane made in the laboratory as well as obtain in the field is

being undertaken at NBS.
- 6 -

6 . REFERENCES

[ 1] W. C. Cullen, "Solar Heating, Radiative Cooling and Thermal Movement -

Their Effects on Built-Up Roofing", NBS Technical Note No. 231 (Dec. 1963).

[2] W. C. Cullen , "Effects of Thermal Shrinkage on Built-Up Roofing", NBS

Monograph 89 (1965)
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SURFACING (MINERAL OR SMOOTH)

4 PLY BUILT-UP MEMBRANE.

2 ONE INCH LAYERS EXPANDED

POLYURETHANE INSULATION.

DECK (2" CONCRETE OR 3/4" PLYWOOD)

I8"XI8','

COPPER- CONSTANTAN

THERMOCOUPLES.

9

SURFACING (MINERAL OR SMOOTH)

4 PLY BUILT-UP MEMBRANE

DECK (2" CONCRETE OR 3/4" PLYWOOD)

18" X 18". COPPER -CONSTANTAN

THERMOCOUPLES.

*

Figure 1. Schematic diagram of typical built-up roof

specimens exposed outdoors.
Figure 2 . Built-u roof sections exposed at Washington , D
Q

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4.

Effect

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surface

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the

solar

heating

of

built-up

membraires

during

summer

exposure.
FIGURE

5

.

THERMAL

MOVEMENT

MEASUREMENT

TECHNIQUE.

CONCAVE HAMMOCK

tetrahedral

Figure 7. Illustrations of irregular- shaped roofs.