NATIONAL BUREAU OF STANDARDS REPORT

8905

PERFORMANCE OF ROOFINGS IN COLD CLIMATES

by

William C. Cullen

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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listing of its four Institutes and their organizational units. Institute for Basic Standards. Applied Mathematics. Electricity. Metrology. Mechanics. Heat. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radiation Physics. Radio Standards

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

421.04-12-4210447 30 June 1965 8905

by

William C. Cullen

Organic Building Materials Section

Building Research Division

Institute for Applied Technology

Sponsored by

Office of the Chief of Engineers

Department of the Air Force

Bureau of Yards and Docks

IMPORTANT NOTICE NATIONAL BUREAU OF S

for use within the Government, and review. For this reason, tl whole or in part, is not authr Bureau of Standards, Washing

the Report has been specificall

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ess accounting documents intended

> subjected to additional evaluation

e listing of this Report, either in ie Office of the Director, National

y the Government agency for which

copies for its own use. <NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL OUREAU OF STANDARDS



PERFORMANCE OF ROOFINGS IN COLD CLIMATES

by

William C 0 Cullen

1 . INTRODUCTION

The National Bureau of Standards was requested by the Office of the

Chief of Engineers, U. So Army; the Directorate of Civil Engineering,

U. S. Air Force; and the Bureau of Yards and Docks, U» S. Navy, to

develop information on problems relating to the performance of roofing

systems in cold climates and to provide technical assistance to engineering

personnel in the solution of existing problems. In this connection, a survey of roofing systems was conducted on selected military installations

in the State of Alaska during May 1965 as a task under Project 4210447,

Performance of Roofings, Tri-Service Engineering Investigations of Building

Construction and Equipment, National Bureau of Standards

The conduct of the survey consisted of "on the roof" observations of typical

roofing systems by an inspection team including representatives of the

National Bureau of Standards; U, So Army North Pacific Division; Office of

the Alaska District Engineer; Headquarters, U. S« Army, Alaska; and Headquarters, Alaska Air Commando

Critical inspections were made at the following installations on the dates

indicated

aElmendorf A.F,B., Anchorage 17 May 1965

b 4 Fort Richardson, Anchorage 18 May 1965

c

AC&W Site, Unalakleet 19 May- 1965

d. Fort Greeley, Big Delta 20 May 1965

e

Tracking Station, Donnley Flats 20 May 1965

f „ Eielson A.F t B*, Fairbanks 21 May- 1965

S' Fort Wainwright, Fairbanks 21 May 1965

In addition to the inspections, round-table discussions were held at each

installation with engineering personnel experienced with the design, construction, maintenance and performance of roofing materials and systems

in Alaska.

This report gives our observations of the performance of roofing systems

in cold climates as well as our opinions and recommendations based on the

observations and discussions. Further, this report discusses the effectiveness of the recommendations of the Alaska Roofing Board which convened in

Anchorage, Alaska, in August 1957. The author was a member of this six-man

board

- 2 -

2. CLIMATOLOGICAL DATA

The climate of Alaska varies from extreme cold during the winter months to

mild temperatures during the summer months. The extremes in the climates

including temperature, wind velocity, snowfall, and rainfall are illustrated by the weather data for each installation visited (Table 1).

3. OBSERVATIONS AND COMMENTS

Various and sundry roofing materials and systems, both conventional and

unconventional, were observed at each installation. These included

bituminous built-up systems and fluid-applied elastomeric systems for

flat decks, as well as metallic and composition roofings for sloping

decks. A view showing the miscellaneous types of roofings which were

observed on one installation is shown in Figure 1

Historically, in Alaska the bituminous built-up roofs have presented

the more serious and costly problems when compared to other roofings

(this is also true for other areas). This fact is clearly illustrated

by information furnished to us by one installation regarding roof repairs

completed during a 7~year period which is reported in Table 2. Incidentally,

the cost of repairs of built-up roofs on this station during the period

amounted to about $900,000 Consequently, a large portion of this report

is devoted to the performance, maintenance, and repair of bituminous

built-up roofing systems.

3.1 Bituminous Built-Up Roofing Systems

3.1 1 Components

a. Waterproofing Membrane

For many years the conventional multiple-ply bituminous built-up membrane has been used to cover structures having low slope (usually

flat) roof decks in Alaska. Prior to 1958, asphalt was the predominately used bitumen, but since then both coal- tar-pitch and low-slope

(dead-level) asphalt have been used in the application of these roofs

Bituminous-saturated organic felts accounted for the large percentage

of reinforcing fabrics employed although some asbestos and glass have

also been used.

TABLE 1„

ALASKA

CLIMATOLOGICAL

DATAw

pi 11 c 1 G 00 00 o co 50 50 5 1 CD CO CO m 50 50 50 H 1 £ g B i g 0 g <3 1 Pi pM 1 w O gD g Di X* w i G 50 50 50 o 05 05

EH ggi £ 00 oo 00 05 05 05 igg 05 05 05 CO CO co g g CM CM 50 50 05 O'. g cd e o a • • • X H g aj co »— 1— r— G i 23 t— r— 1— *— »

< CD g >5 gi M 6g O 05 05 50 CO CO CO

<3 g g X 00 00 05 1^

Pi g jg • • e • e • 0 s 00 00 05 50 oo oo ggg

r— gggg G 05 05 CM CM CM g cd • • • • • X H g cd 05 05 co m O O X cfl g 23 m m co co 50 50

<3 a) i fe g 6 g e 50 50 r^. 05

m in s c g X e • o « e > m

C/5 •H i cd CM CM CM CO 05 g 23 CO CO 00 50 CO co i

gg *“ ' ' ' 4J g CO g 3 g 50 8 G

>-< i <3 H g M g U ! TJ o g H X g • G W & g X in in r- in m LO O > s g cd r— T— 05 05 05 CO 8 23 *“ T— Q g 50 2 g C M g H 2 g 4-4 g O i O g Pi gg G g 4=1 ,X 2 g a) 0) Q) cd co CO CO O g 00 00 Q) 4-> M -X G M g cd cd t—

H G G pH H g u u -X cu cd cd <3

<3 0 o o cd Q X X o g X X H H u 4-4 o g o o G 50 c H •H O

b-4 8 c G G “H G G S <3 <3 P co Pm Pm 4-4 g M g O g a g Q) g Pi g G 4-1 g CO o 2 i pH co >5 50 mo o g <3 XI CD CO •H <v M g u f-4 Pm u o H g 14-1 cd CD <u <3 5 u < g u X 4-4 CD G 3

»4 g o u -H H G •H o 4 i T) c H CO O O cd CO

<3 g G pi co 32 -

H g a ts 4-4 rH -1

co g B o u CD 9 25 i rH 4-1 a O •H u M g w pH <3 Pm w Pm

TABLE 2, ROOF REPAIR DATA

TYPE OF ROOFING

Bituminous Built

Asphalt Shingles

TOTAL NUMBER OF % REQUIRING

NUMBER OF SQUARES REPAIRED REPAIRS

SQUARES SINCE 1957 SINCE 1957

Up 42,000 30,000 71 . 57o

3,000 350 11 . 7%

Metallic Roofings 350 10 6,7%

There was serious disagreement among engineering personnel regarding

the use of a mineral surfacing (gravel) to protect bituminous built-up

roofs. We were aware of this disagreement at the onset of the program

and as a result both smooth" surfaced and gravel-surfaced roofs were

observed during the survey and their performances were evaluated

critically in terms of the surfacing employed,

b» Thermal Control Element

The temperature extremes experienced in Alaska make the use of a thermal

control element in the roofing system mandatory,, For economical considerations, the insulation was frequently located between the roof deck and the

membrane although it was sometimes placed beneath the roof deck*

Prior to 1958, several types of insulating materials were used such as fiberboard, mineral board, fibrous glass and cellular glass. However,

cellular glass has been used predominately for "on top of the deck"

installations since that time,

c» Vapor Control Element

In cold climates such as Alaska, a vapor-control element, which is always

placed on the warm (low-vapor pressure) side, is necessary to restrict

the flow of moisture vapor from the interior of the structure into components of the roofing system. In roofing applications in Alaska, the

vapor barrier was generally placed between the roof deck and the insulation and usually consisted of two plies of 15-lb. asphalt-saturated felt

sealed with hot bitumen

In cases where the insulation was placed beneath the deck, the vaporcontrol element was located in the structure and supplemented by

ventilation.

d. Structural Roof Decks

Concrete decks, both poured and precast, have been used frequently as the

structural platforms for roofing systems on low slopes. Wood decks, both

plywood and T & G planks, have also been used to a large extent especially

on family housing units. In many cases a wood deck was constructed over

an existing flat concrete deck to provide a sloping surface, A case in

point is shown in Figure 2 which proved to be most successful.

In some instances, metal decks were used with an insulation provided

between the deck and the roofing membrane.

e« Flashing Systems

The function of flashings is to provide a water-tight junction between

the roofing material and other parts of the structure. Flashings are

the most vulnerable part of the roof since most leaks result from

failure in these areas. We observed that, for the most part, conventional plastic (bituminous built-up type) flashings have been used

in Alaska in areas such as parapet walls, skylights, ventilators, and

other vertical surfaces. We also observed the use of "pitch pockets"

and metallic flashings at vent pipes and stacks and other projections

through the roofing.

Metallic flashings used alone or in conjunction with bituminous built-up

flashing were found at expansion joints and edge flashings. In these

cases the metal to bituminous transitions were frequently observed below

the ponding water line.

3.1.2 Factors Affecting Roof Performance

a. Moisture

From our field observations, our experience gained by service on the

Alaska Roofing Board, and from discussions with engineering personnel

in Alaska, we are of the opinion that the most serious and costly

problems with roofings resulted from moisture entering into one or more of the roofing system components. The invasion of water into the

roofing system resulted from one or more of the following causes:

1. Failure of the watertight membrane.

2. Failure of flashings and appurtenances.

3. Moisture entrapped in the system prior to or during construction

4. Inadequate condensation control.,

The moisture in the system contributed to premature failure of the

waterproof membrane which was evidenced by blistering, wrinkle formation and subsequent cracking. Figure 3 shows the early indication of

this type of deficiency. In addition, an appreciable accumulation of

moisture in the insulation results in a reduction of its thermal

efficiency

- 5

-

b. Thermal Movement

Investigations, by the author, of roofing failures in cold climates over

a period of many years have revealed that membrane shrinkage has been

an important factor in both membrane and flashing failures. It was

therefore anticipated that this factor would be a frequent cause of

roofing failures in Alaska. However, our observations indicated that

thermal shrinkage was of minor concern when compared to other factors.

In fact, only three cases were observed in which thermal shrinkage was

suspect c Figure 4 shows a serious failure attributed to thermal shrink"

age in the form of a roof split which was observed on a cold storate

warehouse. Figure 5 shows a repaired area which is again showing signs

of a splitting failure due to thermal movement.

c. Roof Slope and Drainage

Our observations indicated that the performance of the built-up roofing

system appeared to be related to the slope. The steeper the slope the

better the performance. Even a slight slope (1 /4-inch per foot) which

provided positive drainage was reflected in an increased performance

of the roofing membrane.

The ponding of water in low areas on roofs definitely contributed to

premature failure and resulted in specific problems such as the chemical

degradation of the bitumen, physical deterioration of any exposed felts

and frequently the disintegration of the cellular glass insulation.

These factors were observed on most level roofs and in particular on

those unprotected with gravel surfacing.. Figure 6 illustrates the many

areas of one roof where water collected and stood. Many of these areas

exhibited evidence of early membrane failure. Invariably the roof drains

when present were located at high areas on the roof and, of course, contributed to the ponding of water.

Our observations of a gravel-surfaced coal-tar-pitch roof on the composite building at Unalakleet revealed that water, 2 to 4 inches in

depth, covered most areas of the roof. Personnel at this station

reported that this condition existed during most of the year. A

slight rupture in this roofing membrane could result in serious and

costly failures. It was the consensus of the inspection team that

roof slopes and adequate drainage should be required in these areas.

FIGURE

3.

GRAVEL

SURFACED

ROOF

SHOWING

FIGURE

4.

ROOF

MEMBRANE

SPLIT

ATTRIEFFECTS

OF

MOISTURE

ENTRAPMENT

IN

THE

BUTED

TO

THERMAL

SHRINKAGE.

ROOF

SYSTEM.

- 6 -

d„ Flashings

Inadequately designed, improperly installed and defective flashings were

observed on roofs located at each Installation, In our opinion, these

deficiencies accounted for a large percentage of the reported failures.

Figure 7 shows a serious failure which is typical of such a design at

the flashing of an earthquake joint, which resulted in leakage. This was

the only failure on a roof which otherwise provided good service for

over 5 years. We believe this to ba a poorly designed flashing system

for an expansion joint.

The unauthorized installation of antennae have also been the cause of

leakage in many roofing systems. Figure 8 illustrates an extreme case

where coping, roofing and flashing were punctured.

Metal to bituminous transitions in flashing systems should be avoided

wheneven possible and should never be allowed beneath the standing

water line. Figure 9 shows a typical failure at an edge flashing,

while Figure 10 is an architectural drawing of the condition. We

observed this type of failure more than any other single failure during

the survey. The seriousness of this defect when it occurs below the

standing water line is readily apparent,

e. Smooth Surfacing vs. Gravel Surfacing

Approximately one-half of the built-up roofs which were inspected were

surfaced with gravel, while the remaining half were so-called smoothsurfaced roofs, i,e„, coated with hot asphalt, hot coal-tar-pitch (one

case only), asphalt emulsion, or a cut-back type asphalt roof coating.

Our observations indicated that the better performance was obtained

with the gravel-surfaced roofs, although adequate service was obtained

with many of the smooth roofs. It should be pointed out here that

there was disagrement even among the members of the inspection team

regarding the merits of mineral surfacing. Nevertheless, we are of

the opinion the evidence is in favor of mineral surfacing regarding the

performance of the total system. Indeed in at least two cases, sections

of gravel-surfaced roofing exposed side-by-side (on the same structure)

with their smooth- surfaced counterparts appeared in better condition

despite an age difference of a number of years. Figure 11, typical of

many surfaced built-up roofs, shows the appearance after about 14 years

exposure in the Anchorage area with little or no maintenance. On the

other hand, many smooth-surfaced built-up roofs exhibited deficiencies

common to this type of roofing, such as chemical degradation of bitumen,

ailigatoring, checking and surface cracking. These defects are not

serious in themselves but do tend to shorten the effective life of

the roof membrane.

FIGURE

7.

DEFECTIVE

FLASHING

AT

EARTHFIGURE

8.

UNAUTHORIZED

INSTALLED

QUAKE

JOINT

AFTER

UNSUCCESSFUL

ANTENNAE

WHICH

RESULTED

IN

COPING

ATTEMPTS

TO

REPAIR.

FLASHING

AND

MEMBRANE

FAILURES.

7

Our experience with roofings in all areas has indicated that smoothsurfaced roofs require considerably more maintenance (recoating every

3 to 5 years) than their gravel-surfaced counterparts.

f. Insulations

The use of insulation in the roofing system has a direct effect on the

durability of the roofing membrane. We observed that the performance

of a membrane placed on the insulation was somewhat inferior to a similar membrane placed directly on the structural deck. Although

this evidence would indicate that a "below the deck" location is desirable, we are of the opinion that this practice is not economically

feasible in the majority of cases. Further experience in Alaska ha."

shown that an adequate and serviceable roofing system can be constructed

with the insulation located between the deck and the membrane if proper

design, material and application specifications are enforced by construction inspection.

Various types of insulations were used in the Alaska area prior to 1957.

However based on the recommendations of the Alaska Roofing Board, the

cellular glass type has been used in the majority of installations since

that time. In general, this material has performed adequately in service

although some deficiencies were brought to our attention. The relatively

poor resistance to wind uplift of the paper-backed type contributed to

serious wind damage in one location. It was reported that the failure

occurred at the interface of the cellular glass and its paper cover.

In three cases, we observed indications of the disintegration of cellular

glass extending down as much as 1/2 inch from the surface. In each case

water had penetrated the membrane and we believe the repetitive freezing

and thawing action of the water resulted in this disintegration. Figure

12 shows an area where this deficiency was observed

The performance of other types of insulations such as fibrous glass,

mineral and fiber board, cork, etc., was satisfactory as long as they

remained dry,

g. Bitumens

Asphalt and coal- tar-pi tch have been used for many years for the construction of built-up roofs in Alaska. In the survey we observed that

each gave satisfactory service. We believe that other factors contribute much more to roof performance than the choice of bitumen.

ROOF 5

PLIT

FIGURE

11.

GRAVEL

SURFACED

ROOF

AFTER

FIGURE

12.

DISINTEGRATION

OF

CELLULAR

14

YEARS

SERVICE.

ANCHORAGE,

ALASKA.

GLASS

INSULATION

(EXTENDING

1/4

TO

1/2

INCH

FROM

SURFACE)

ATTRIBUTED

TO

FREEZING

AND

THAWING

ACTION

OF

ENTRAPPED

WATER.

- 8 -

It was interesting to observe that a smooth- surfaced coal-tar -pitch

roof was giving good service after many years exposure despite the

fact that mineral surfacing is always recommended for this type of

roof*

3*2 Roofing Systems on Sloping Decks

There was complete agreement that roofing systems on steep slopes have

a history of excellent service in Alaska regarding watertightness and

durability,, Figures 13, 14, 15, and 16 show roofings which are typical

of those which have served well. These include asbestos-cement, asphalt

shingles, roll roofings, metallic shingles, and various other metal

roofings* In fact, copper shingles which were observed in the Fairbanks

area were still giving adequate service after 24 years service. This

is considered excellent service for any roofing material in any climate.

Wind damage to asphalt shingles has presented some problems in the past

but this deficiency has been largely overcome by specifying windresistant shingles or sealing down the tabs of free-tab shingles with

an asphalt plastic cement*

Glaciation and formation of ice dams are problems common to steep roofs

in cold climates* Glaciation, although not directly connected with roof

performance must be considered in terms of the hazard it presents to

life and property (including roof damage)* On the other hand, the

formation of ice dams at the eave of a roof frequently cause leakage

where non- continuous roofings are involved (shingle type), A metal

eave strip varying in width from 12 inches to 3 feet or more has been

used (Figures 13 to 16) to reduce the potential hazards,

3*3 Fluid-Applied Organic Roofing Materials

Non-bi numinous f iuid~applied roofing systems were observed on flat

concrete decks at Unalakleet and Donnley Flats* In two cases, NeopreneHypalon materials were used and in the other, an epoxy coating was

applied* Although the performance of each material which was observed

was considered to be satisfactory, we believe the Neoprene-Hypalon

systems gave the better service in that they were less susceptible

to rupture from discontinuities in the concrete deck, provided better

adhesion to the deck, and exhibited the better weathering characteristics,

4, MAINTENANCE AND REPAIR

Inspection, maintenance, and repair procedures for roofing systems

appeared to be well established for the installations included in the

survey. In general, conventional methods, consistent with the climate

of Alaska, were employed and the results were good* For example.

ggM M

SC p

co IjM H & ^ m a o

Pm 25 CO M

«$ CO .1

sj- IS

fa &

*Ra co R

-< - M CO *a CO w< W H H

si* M O' U a ^ E « >sJ ga H M . R*S 3 §io • cT&l m w W

CO 5 uS

9

Figure 17 illustrates the condition of a roof selected for the application

of a repair membrane prior to a failure. Figure 18 shows a roof of a similar structure after repair was accomplished. We believe that this

procedure will extend the useful life of the roof for many years. On

the other hand, unconventional maintenance techniques were also observed.

These in many cases compounded the failure rather than corrected it e Figure 19 shows the results of applying a glass fabric over a gravel*

surfaced roof without removing the surfacing. Figure 20 illustrates

cracking failures resulting from the use of thick surface coatings

without the protection of gravel surfacing.

We were pleased with the results of the roof inspection and maintenance

programs being conducted at each installation and it is our opinion

that these procedures have contributed to the noticeable improvement

of roofing performance in Alaska during the past 8 years.

We strongly believe that failure to recognize and correct minor defects

and deterioration in their earliest stages are the greatest causes of

premature roof failures and frequently result in costly repairs and

replacement. We further believe that funds which are made available

for inspection, maintenance and repair programs for roofing systems will

ultimately result in enormous savings.

5. CONCLUSIONS AND RECOMMENDATIONS

A critical review of information and data, which were obtained during the

survey and were based on histories, reports, discussions, and observations

of roof performance, revealed a definite improvement in the performance

of roofings in Alaska since 1957. The improved performance can be

attributed to a large extent to the implementation of recommendations

set forth by the Alaska Roofing Board. However based on the results of

eight more years of experience, we do not concur with all the recommendations of the Board. These deviations are reflected in the suggestions

which follow.

In conclusion, we submit the following suggestions regarding design,

material and application procedures which we believe will mitigate many

serious problems with roofing system performance in cold climates

which were observed during the survey.

H W

£5S H H J < M fii

1=)

W

PQ 2

•—

Mw 11O W FIGURE

19.

EXPOSED

GLASS

FABRIC

WHICH

FIGURE

20.

SURFACE

CRACKING

OF

AN

WAS

USED

AS

INA

REPAIR

MEMBRANE

OVER

ASPHALT

EMULSION

ROOF

COATING

APPLIED

A

GRAVELSURFACED

BUILT-UP

ROOF.

OVER A

THICK

COATING

OF

HOT

ASPHALT.

10 -

5.1 Built-Up Roofs

5.1.1 Design Considerations

a. Slope

Bituminous built-up roofs should be designed and constructed to provide a minimum slope to drain of 1/4 inch per foot (1/2 inch where

possible) and to insure that no negative slope to drain will occur

under any design load at any time.

Roof drainage systems should be designed so that drains are located

at low areas of the roof.

b. Flashings

Figures 21 , 22 , 23 , and 24 are flashing systems which are suggested

for use at the locations indicated.

Wood backing when used in flashing systems should be fastened to the

same structural system as the roof covering to preclude damage from

differential movement between building elements «, Antenna installation should be made under the supervision of the post

engineering personnel.

c. Insulation

We have seen no evidence to warrant the continued use of cellular

glass on an exclusive basis for l0 on the deck69 installations. Other

insulating materials such as fibrous glass, mineral board, fiberboard, etc., will also give adequate service when properly installed

in an adequate roofing system,

A vapor barrier having a mini-mum vapor permeance rating of 0.5 perms

should be specified for use between the deck and insulation.

d. Membrane

Low-slope asphalt (sometimes referred to as dead-level bitumen) or coal-tar-pitch conforming to applicable specifications is suggested

for use in the application of all built-up roofs on a slope of less

than 1/2 inch per foot.

FIGURE 21. SUGGESTED FLASHING DESIGN

AT EDGE FLASHING.

A/E OPRENS G-/\ SKE T

W/TH SCKEW PASTEHE

O HOT 3TR/P /H

METAL. H/TH R OOE/N&-

US£ PL ASP/HE APPLICABLE

TO DECK. SPEC/F/CA J/ ON.

FIGURE 22. SUGGESTED FLASHING DESIGN AT

EDGE FLASHING. NOTE THAT THE METAL IS NOT STRIPPED INTO THE BITUMINOUS

ROOFING.

FIGURE 23. SUGGESTED FLASHING DESIGN

AT EXPANSION OR EARTHQUAKE JOINTS.

FIGURE 24. SUGGESTED FLASHING DESIGN

AT PARAPET WALLS.

- 11 -

Gravel or other suitable mineral surfacing should be used as surfacing

on all bituminous built-up roofs on a slope of 1/2 inch per foot or

less. The surfacing should conform as nearly as possible to the re5.1.2 quirements of ASTM Designation D1863.

Application Considerations

The construction season in Alaska limits roofing applications to about

4 months or less each year. We believe that the waving of some of the

conventional restrictions in application techniques due to temperature

will actually result in improved roof performance. For example, roof

application could be allowed when the ambient temperature is below the

limit generally specified if other conditions are satisfactory for roo;. application or repair (dry weather, structure and materials). The

judgment of the engineer in charge should largely govern in such cases.

5.2

Systems for Sloping Roofs

Roofing systems for sloping roofs have given satisfactory performance

and it is predicted they will continue to do so as long as adequate

material, design and application specifications are enforced.

In all asphalt shingle applications we suggest the use of wind-resistant

shingles on all slopes to reduce wind damage. In addition, we suggest

the use of a double underlayment of felt on all asphalt shingle installa

tions on slopes of 5 inches in 12 inches or less. This method will prevent the infiltration of water due to the formation of ice dams. The

underlayment should consist of two layers of 15-lb. asphalt saturated

felt lapped 19 inches. The lap of the double underlayment should be

sealed with a continuous layer of asphalt plastic cement from rfhe

eave extending up the slope to a line at least 24 inches inside the

interior surface of the exterior wall.

5.3

New Roofing Systems

a. Fluid-Applied Systems

The neoprene -Hyp a I on fluid-applied roofing system is suggested for both

exposed and unexposed concrete roof decks when the more conventional

systems cannot be used,. The system should be applied to a dry deck and

should consist of a primer, 2 coats of a neoprene coating, and two coats

of Hypalon coating. The dry film thickness of the system should not be

less than 0,020 inches.

12

b. Elastomeric Sheet Roofings

Considerable interest was expressed in the utilization of some of the

elastomeric sheet roofings in lieu of the bituminous built-up roofing

system. Several of these roofings are currently available as follows:

1 , Polyvinyl Fluoride film (Tedlar) factory- laminated to a felt of elastomer-bonded asbestos,

2* Chlorosulfonated Polyethylene film (Hypalon) factorylaminated to a felt of elastomer-bonded asbestos.

3. Polyisobutylene film factory- laminated to a felt of

plastic-elastomer bonded asbestos.

4„ Butyl Rubber Membrane,

A roof system can be considered adequate only when it has had a history

of good performance exceeding 10 years in a climate such as Alaska.

Obviously in the case of these materials this history is lacking.

Therefore, we are unable to predict now their long-term performance

in cold climates. We are of the opinion, however, that they possess

good possibilities for special applications on small areas where the

more conventional systems have not performed well. However, sufficient

exposure data has not been developed to recommend their extended use

in Alaska at this time.

6 . ACKNOWLEDGMENT

The author expresses his sincere appreciation to the many persons

representing Ih S. Army Engineers, Headquarters, U. S, Army Alaska;

Headquarters, Alaska Air Command, and to engineering personnel of the

installations visited for their excellent cooperation and courtesies

extended during the roof survey in Alaska. Special thanks are due to

the following who took time from their busy schedule to accompany the

author as members of the survey team: Messrs. Joe Cange, 0* V. Kola,

Don McGregor, Harry Roberts, and Ed Swanson

We also thank Mr. Jay Humphreys, President, Tamko Products, Xnc 9 , for

his permission to use flashing details from their 1963 catalog in this

report

USCOMM-NBS-DC