United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

Research

Paper

FPL–RP–543

Roof Temperatures

in Simulated Attics

Jerrold E. Winandy

Rhett Beaumont
Abstract

The degradation of wood treated with fire retardant (FR)

chemicals in roof systems is a problem of major national

significance. Understanding of this phenomenon is limited by

lack of information on how the performance of FR-treated

wood in the laboratory correlates to that of FR-treated wood

in the field. In this study, five outdoor field exposure chambers were constructed near Madison, Wisconsin, in the summer of 1991. These structures were intended to simulate the

“attics” of multifamily structures for which model building

codes sometimes allow the use of FR-treated roof sheathing.

Interior attic air, exterior air, inner and outer sheathing, and

internal rafter temperatures of black- and white-shingled

chambers were monitored. Temperatures were measured using

thermocouples and recorded over a 3-year period from October

1991 through September 1994 using a datalogger/multiplexer

device. Overall, the plywood sheathing in black-shingled roof

systems tended to be 10 ̊F to 15 ̊F (5 ̊C to 8 ̊C) warmer during the midafternoon of a sunny day than the plywood in

comparable white-shingled roof systems. The maximum

sheathing temperatures recorded were 168 ̊F (76 ̊C) for blackshingled roofs and 147 ̊F (64 ̊C) for white-shingled roofs.

The results suggest that roof-sheathing plywood and rooftruss lumber temperatures, which are the primary factors that

influence thermal degrade of FR-treated materials, are primarily controlled by solar gain rather than attic ventilation or

attic insulation. These results are tempered by the fact that

the effect of moisture content was not evaluated nor was

moisture controlled by attic ventilation.

Keywords: Roof temperature, plywood, roof sheathing, rafter,

thermal degrade, fire-retardant treatment, shingles, attic

ventilation

September 1995

Winandy, Jerrold E.; Beaumont, Rhett. 1995. Roof temperatures in

simulated attics. Res. Pap. FPL–RP–543. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory. 14 p.

A limited number of free copies of this publication are available to the

public from the Forest Products Laboratory, One Gifford Pinchot Drive,

Madison, WI 53705–2398. Laboratory publications are sent to more than

1,000 libraries in the United States and elsewhere.

The Forest Products Laboratory is maintained in cooperation with the

University of Wisconsin.

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Persons with disabilities who require alternative means of communication

of program information (braille, large print, audiotape, etc.) should contact

the USDA Office of Communications at (202) 720–2791. To file a

complaint, write the Secretary of Agriculture, U.S. Department of

Agriculture, Washington, DC 20250, or call (202) 720–7327 (voice), or

(202) 720–1127 (TTD). USDA is an equal employment opportunity

employer.

Acknowledgment

The authors acknowledge the financial assistance of the New

Jersey Department of Community Affairs and the technical

assistance of Mike Grambsch and Earl Geske, who monitored

and programmed the temperature datalogging equipment at

the Valley View test site. We also wish to thank CertainTeed

Corporation for their donation of the roofing materials used

on the outdoor simulated-attic exposure chambers.

Contents

Page

Problem.....................................................................1

Background.................................................................1

Method......................................................................3

Exposure Chambers..................................................3

Temperature Monitoring System.................................3

Results and Discussion.................................................5

Comparison of Black- and White-Shingled Chambers......6

Difference in Yearly Temperature Histories....................6

Temperature Trends...................................................8

Concluding Remarks....................................................9

References..................................................................9
Problem

The degradation of wood treated with fire retardant (FR)

chemicals in roof systems has been reported in thousands of

cases over the eastern half of the United States (NAHB

1990). Understanding of this wood deterioration phenomenon

is currently limited since there is little information that correlates the results of laboratory experiments using steady-state

and cyclic temperature exposures to actual diurnal (that is,

daily cyclic) field temperature histories experienced by FRtreated wood in service. This lack of a consensus “lab-tofield” correlation has inhibited the ability to predict thermalinduced degradation of FR-treated wood in the field from

thermal-degradation rates derived in the laboratory.

Current model studies have generally been limited to

isothermal rate studies performed in the laboratory with

selected model FR chemicals. Factors other than temperature

appear to play a secondary role in the degradation of FRtreated wood. These secondary factors, which are currently

being studied in greater detail in additional laboratory experiments, include relative humidity (as it influences wood moisture content) and moisture content cycling. Each factor

(temperature and moisture content) contributes to the rate of

thermal-induced degradation. However, a significant problem

is the lack of reliable and scientifically reproducible data that

relates the performance of FR-treated wood products in

laboratory exposures to performance in the field. Accurate

modeling of the degradation of FR-treated and untreated wood

will require obtaining sufficient and comprehensive data from

both laboratory and field studies to establish creditable acceptance criteria for evaluating roof sheathing performance.

Our study consists of three phases:

1. construction and monitoring of five field exposure

chambers near Madison, Wisconsin,

2. exposure of side-matched specimens treated with

various FR treatments in either a steady-state 150 ̊F

(66 ̊C)/75-percent relative humidity laboratory exposure

or a diurnal/seasonal exposure in one of these five field

chambers, and finally

3. mechanical evaluation and development of a lab–field

correlation factor.

This report presents actual roof temperature data from

Phase 1 of this experiment obtained over a 3-year period

from October 1, 1991, through September 30, 1994.

In Phase 2 of our experiment, the five field exposure chambers serve as platforms in which nominal 0.5-in.- (standard

12-mm-) thick, 4- by 22-in. (100- by 559-mm) plywood test

specimens are being exposed to diurnal/seasonal cyclic field

conditions. The inside of each exposure chamber was constructed such that 96 plywood samples could be inserted into

the frames, providing direct contact with the shingle/roof felt

roofing membrane. A future report will describe the potential

for thermal degrade of untreated controls and various generic

FR treatments exposed to either simulated field conditions in

a field exposure chamber or to a steady-state high-temperature

environment in the laboratory at 150 ̊F (66 ̊C) and 75 percent

relative humidity.

Background

Fire retardants were first used in the United States by the

Navy in 1895 (Moreel 1939), but use was discontinued in

1902, in part because of their corrosiveness to fasteners.

Preliminary research by Prince (1915) and the Forest

Products Laboratory, USDA Forest Service, in the 1930s

(Hunt and others, 1930,1931,1932; Truax and others,

1933,1935) led to the use of combinations of ammonium

sulfate, diammonium phosphate, borax, and boric acid as

commercial fire retardants. Materials treated with these

systems have been used successfully in structures at or near

room temperature for more than 50 years. Histories of FRtreated wood and its acceptance by building codes and in

treating standards, respectively, can be found in the literature

(Catchpole 1976, Barnes 1994).

In the 1970s, concern over hygroscopicity and fastener corrosion led the industry to develop improved systems with lower

corrosion potential and hygroscopicity, known generically as

second-generation fire retardants (Davies 1979). These

systems entered the marketplace in the early 1980s. At nearly

Roof Temperatures

in Simulated Attics

Jerrold E. Winandy, Research Wood Scientist

Forest Products Laboratory, Madison, Wisconsin

Rhett Beaumont, Consulting Engineer

Hazard Engineering, Inc., Morton Grove, Ilinois
2

the same time, a change in the model building codes allowed

the use of FR-treated plywood sheathing as a replacement for

noncombustible roof deck and parapet–wall systems in multifamily structures. Because of the energy crisis, construction

practices were also changed to provide more resistance to

passive indoor air infiltration, and designers relied more on

built-in passive attic ventilation or active mechanical attic

ventilation. In addition, structures were better insulated in an

attempt to make them more thermally efficient. Each change

had the potential for affecting the in-service temperatures to

which wood roof systems were exposed.

Heyer (1963) reported temperature histories for wall and roof

systems for six houses and one office building located across

the United States. The houses were located in Tucson,

Arizona; Athens, Georgia; Portland, Oregon; Diboll, Texas;

and Madison, Wisconsin. The office building, the original

headquarters of the Forest Products Society, was also located

in Madison, Wisconsin. The results of this study found that

the maximum temperature of the roofs could reach 170°F

(76°C), but that the cumulative duration of temperatures over

160°F (71°C) was not observed to exceed 21 h in any one

year. In addition, the cumulative duration of temperatures

over 150°F (66°C) was not observed to exceed 64 h in any

one year, which is important considering that design standards for wood (AF&PA 1991) require a strength property

adjustment for sustained exposures above 100°F (38°C) and

greater adjustment for prolonged exposure above 150°F

(66°C).

Several studies modeled the roof temperatures attained by

structural buildings. Ozkan and Wilkes studied the temperatures of the surface and various components in flat roof

systems, but they did not consider wood sheathing temperatures. In the study by Ozkan (1993), temperatures on roofing

surfaces of a field station in a very hot, dry Arabic climate

reached 200°F (93°C) during April 1989 to November 1990.

The primary use of this station was to observe the effects of

weathering and to measure the temperatures of the bituminous and polymeric waterproofing membranes in addition to

that of thermal insulation materials. In the study by Wilkes

(1989), metal roof temperatures reached as high as 163°F

(73°C) during January and May in eastern Tennessee. For

more exposure temperature histories for shingles the reader is

referred to publications by the National Bureau of Standards

(NBS 1979) and Blackenstowe (1987). The temperatures

histories discussed hereafter pertain to wood components of

roof systems.

Computer models have been developed that predict the average temperature and moisture content of plywood roof sheathing and other lumber roof members based on various construction details, materials, ventilation factors, and solar gain

(that is, radiation load) on the roof. A model studied by the

American Plywood Association predicted that flat-roofed

systems with a black membrane might experience high-end

temperatures of 150 + 5°F (66 + 3°C), 160 + 5°F (71 + 3°C),

170 + 5°F (76 + 3°C), and 180 + 5 F° (82 + 3°C) for up to 36, 13,

5, and 2 h, respectively, over the course of an average year

in Hartford, Connecticut (APA 1989). Wilkes (1989) developed and verified a predictive roof temperature model for

multi-layer nonwood roof systems. However, the model does

not account for moisture flux, which may be critical in wood

roof systems.

TenWolde (1988) described a model (still under development

and needing verification) that estimates that the surface temperature of plywood roof sheathing is dominated by solar

gain and the heat exchange between the roof surface and

ambient air. Diurnal temperature variation and hourly sheathing temperature histories are also influenced by the radiant

energy absorptivity of roofing surface, the pitch of the roof,

and the presence of insulation and attic ventilation. The

TenWolde model predicts that wet plywood sheathing dries

quickly under warm summer conditions. For example, if

plywood with a moisture content of 60 percent is installed,

the plywood moisture content is roughly 15 percent after

1 week and is reduced to 8 percent in roughly 2 weeks. The

model also indicates that the absorptivity of solar/radiant energy of the roofing material has the greatest effect on increasing or reducing the average temperature of the plywood roof

sheathing. If the absorptivity of the roofing material is 0.92,

the model predicts that the maximum hourly temperature for

the roof sheathing plywood is 140°F (60°C) and the maximum predicted exterior roof membrane temperature is 150°F

(66°C). If the absorptivity is changed to 0.2, supposedly representing a metal roof system, the maximum predicted

sheathing temperature drops to 95°F (35°C) and the maximum predicted membrane temperature is 95°F (35°C). The

pitch of the roof has only a moderate influence on reducing

both the exterior surface temperature and the average temperature of the plywood. The TenWolde model also predicts that

the presence of insulation installed directly on the underside

of the sheathing has virtually no influence on sheathing temperature on the top surface but raises the average sheathing

temperature relative to that of the top surface. When the ventilation rate in uninsulated systems is increased from 8 air

changes per hour to about 21, almost no reduction of the

top surface sheathing temperature or average sheathing temperature is predicted.

In 1992, a test facility was constructed at the Building

Research Council of the University of Illinois to measure

heat transfer, moisture movement, and airflow in typical residential attic structures under natural conditions (Rose 1992).

The results of this study showed that during the summer in

Illinois attic ventilation could lower attic air temperature by

28°F (15.5°C) and sheathing temperature by almost 10°F

(5.5°C). However, attic ventilation had only a minor effect

on roof shingle temperature.
3

Method

To obtain the necessary roof sheathing temperature data to

relate diurnal and seasonal-cyclic field exposure to steady-state

laboratory exposures, five field exposure chambers were constructed at the Valley View exposure site near Madison, Wisconsin (43° latitude). On the winter solstice (December 21),

the average incidence angle of sunlight is 19.5° from the

southern horizon and on the summer solstice (June 21), 43°.

Thus, the annual average declination angle in Madison is

31.25°. Considering these facts, the chambers were constructed to face south in a shadeless area open to direct sunlight. In addition, the chambers were also spaced far enough

apart to prevent any one chamber from shading the next

chamber. The exposure chambers are shown in Figure 1.

Exposure Chambers

The 12-ft- (3.7-m-) wide by 16-ft- (4.9-m-) long, identical

exposure chambers were constructed to simulate part of a

typical multifamily attic/roof system in which model building codes sometimes allow FR-treated plywood roof sheathing. To achieve this type of construction, the chambers

simulated in cross section the 1/8- to 3/8-span section of a

48-ft (14.6-m) span, 3:12 pitch roof system in both roof area

and attic volume (Fig. 2). Each chamber was completely

enclosed and kept unventilated. The four exterior walls were

sheathed with 1/2-in.- (12-mm-) thick, 8-in.- (200-mm-)

grooved Southern Pine siding attached to nominal 2- by 4-in.

(standard 38- by 89-mm) wall studs. The exterior surfaces of

each building were coated with one coat of primer and two

top coats of latex solid-color stain or paint. The color of the

stain or paint was light gray, almost white. The walls and

the 5/8-in. (16-mm) plywood and nominal 2- by 10-in.

(standard 38- by 235-mm) joist floor system of each chamber

were not insulated. The chambers were roofed with CertainTeed XT-25 fiberglass roofing shingles that weighed 233 lb

(106 kg) per square.1 These shingles were essentially identical to those used in Champaign, Illinois, to study the behavior of attics constructed and ventilated in various ways (Rose

1992). White shingles were used on two chambers and black

shingles on the remaining three chambers, which allowed us

to address the effect of shingle color on thermal absorptivity.

Because of the gentle slope of the test site, the north side of

the chambers was approximately 12 in. (0.3 m) off the

ground, whereas the south side was about 16 in. (0.4 m)

off the ground.

In 1994, similar exposure chambers were constructed at the

Mississippi Forest Products Laboratory at Mississippi State

University in Starkville as part of an ongoing effort to relate

 

1

The use of trade or firm names in this publication is for

reader information and does not imply endorsement by the

U.S. Department of Agriculture of any product or service.

temperatures in matched northern and southern U.S. roof systems (Barnes and others 1993). The conditions in the Mississippi study are expected to be more severe (that is, higher

solar loading) than those in the Madison study. When available, the data from the Mississippi study will be integrated

with field data from the Madison study.

Temperature Monitoring System

Two of the five field exposure chambers—one black-shingled

chamber and one white-shingled—were instrumented with

nine thermocouples variously located within the structure

(Figs. 3 and 4). In each chamber, the first two thermocouples

(T0 and T1) measured interior chamber temperature at 8 ft

(2.43 m) and 5 ft (1.52 m) above grade, respectively. These

thermocouples were centrally located along the back (north)

wall. The third thermocouple (T2) measured exterior chamber

temperature and was centrally located on the back wall. It was

located 6 ft (1.83 m) above the grade. The fourth thermocouple (T3) was placed in the roof system below the roofing felt

and attached by wood-fiber-based adhesive to the top veneer of

the 3/4-in. (19-mm) plywood sheathing. This thermocouple

was located high in the roof structure: at one-third of the rafter span approximately 4 ft (1.22 m) from the north (ridge)

wall. The fifth thermocouple (T4) was similarly placed in the

roof system below the roofing felt and attached to the top ply

of the plywood sheathing, but it was located lower in the

roof structure: at one-third of the rafter span approximately

4 ft (1.22 m) from the south (eave) wall. These two locations

were selected because small roof systems such as this theoretically might not become as hot as large roof structures

since air heats as it travels across the roof surface. Rose

(1992) reported such a phenomenon affecting sheathing

temperatures when comparing a 30-ft- (9.2-m-) wide system

to a 42-ft- (12.8-m-) span system. However, we believe that

Figure 1—Outdoor field exposure chambers

built near Madison, Wisconsin (latitide = 43.4 ̊

north). Each chamber holds 96 field exposure

specimens. (M95 0057–24A)
4

▼

▼

1.5 ft

4.5 ft

6 ft

5 ft

8 ft

8-ft field exposure chamber (see Figure 3)

Area = 5 x 12 + 1/2(3 x 12) = 78 ft2

 Field chambers have approximately one-half the

 south-facing solar load area and one-half the

 attic volume as a 48-ft roof truss-attic system.

48-ft multifamily roof truss

Area = 144 ft2 (total)

72 ft2 south-facing half section

3

12

3

12

∴

Figure 2—View of field exposure chamber in relation to roof truss of multifamily structure. Field chamber

has approximately half the south-facing solar load area and half the attic volume as that of a 48-ft (14.6-m)

roof truss–attic system. 1 ft2

 = 0.09 m2.

~

➢

3:12 pitch

Specimen

Roof felt

Plywood

sheathing T7

T1

T0

Shingle

T3

T5 T8

Embedded

inside

rafter

~

North

2 x 6 in.

rafter

▼

▼

T6 T4

Specimen

~

Datalogger

T8

T5 T3

Shingles Roof felt

Plywood

Rafters

6

in.

T2

➜ ➜

▼

▼

▼ ▼

5 ft

8 ft

Test specimen

Figure 3—Schematic cross section of instrumented field exposure chamber showing location of

thermocouples (T0–T8) and channels for datalogger/multiplexer.
5

overall the roof systems that we used were able to simulate

thermal loading conditions within the small 4-in. (100-mm)

by 22-in. (559-mm) plywood test specimens in a nearly

identical manner to that experienced by full-sized 4-ft.

(1.22-m) by 8-ft (2.44-m) sheets of treated roof sheathing.

The sixth thermocouple (T5) was attached to the bottom of

the roof sheathing plywood, one-third of the rafter span

from the north wall. Similarly, the seventh thermocouple

(T6) was also attached to the bottom of the roof sheathing

plywood, but one-third of the rafter span from the south

wall. The eighth thermocouple (T7) was used as the external reference thermistor; it was a single channel identical to

both buildings. This thermistor had a rated accuracy of

 + 0.4 ̊F ( + 0.2 ̊C) between −27 ̊F (−33 ̊C) and 120 ̊F (48 ̊C).

The ninth thermocouple (T8) was located within the interior

of the roof rafter/joist. Specifically, this thermocouple was

inserted in the center of the 2- by 6-in. (38- by 140-mm)

cross section at the midspan of the Western Hemlock rafter.

The position of the T8 thermocouple allowed us to correlate

rafter and sheathing temperatures directly to one another and

eventually to solar load as monitored by the U.S. Weather

Service at Truax Field in Madison (~8.5 mi [~13.5 km]

east–northeast of the test site).

A Campbell–Scientific Model CR10 datalogger and a

Model AM416, 32-channel multiplexer were used to collect

and record the temperature data from the 17 thermocouple

locations. The CR10 has a reported accuracy of 0.2 percent

over the service temperature range of −67 ̊F (−55 ̊C) to

185 ̊F (85 ̊C). The datalogger and multiplexer were placed

in a weather-sealed box inside the white-shingled chamber,

on the east wall approximately 6-ft (1.83-m) above the

floor. The datalogger–multiplexer system collected temperature data every 5 min for each exposure chamber; the datalogger was programmed to calculate and record hourly average temperatures. Each week, the hourly data were downloaded to disk with a laptop computer. The set-up of the

datalogger–multiplexer system and a temporarily attached

laptop computer is shown in Figure 5.

Results and Discussion

The fact that the field chambers were neither ventilated nor

insulated means that the results reported here are truly indicative of only such construction. Furthermore, as mentioned earlier, a larger structure might theoretically experience higher temperatures, but to exactly what degree is unknown (Rose 1992). However, we believe that much practical information can be learned from studying the data generated by our field exposure study.

Figure 4—Placement detail of thermocouples

for monitoring temperatures inside field exposure chamber and openings in sheathing plywood intended to accept sample specimens.

All data were recorded with field exposure

specimens in place. (M95 0057–22A) Figure 5—Set-up of datalogger–multiplexer,

temporarily attached to downloadable, portable computer system. (M95 0057–21A)
6

Top-of-sheathing and bottom-of-sheathing temperatures

were monitored at the one-third and two-third roof span

locations midway between the eaves and the ridge

(thermocouples T3–T6). The difference in recorded hourly

temperatures between the top-of-plywood locations

(thermocouples T3 and T4) and between the bottom-ofplywood locations (thermocouples T5 and T6) seldom

exceeded 2 ̊F (1 ̊C). This small difference in temperature

across the span of the structure may be indicative of the

short span or lack of ventilation. Rose (1992) found that

increased ventilation with pitched, cathedral ceiling systems

increased this across-the-span temperature differential. However, subsequent results comparing vented and unvented flatroof systems showed few differences in sheathing temperature between the eaves and the ridge (Rose n.d.). Because of

the small temperature differential between the two sets of

midspan locations in our study, temperature readings for

each set of locations were averaged; this average hourly

value is henceforth reported. The actual number of hours at

given temperatures for the black-shingled and whiteshingled exposure chambers for each 12-month period

between October 1991 and September 1994 are shown in

Tables 1 to 6. Figures 6 to 11 depict these data for three locations in the chambers. In these figures, the abscissa

shows the “exceedence temperature,” which is defined as the

range between some minimum temperature limit and the

next higher exceedence temperature limit; the ordinate is the

number of hours that recorded temperatures at that location

went beyond the exceedence range. Average values of the

3-year test period are given in Figure 12; direct comparisons

between the years are given in Figure 13.

Comparison of Black- and

White-Shingled Chambers

Note that for most recorded locations, the black-shingled

roofs were generally 10°F to 15°F warmer than identical

white-shingled roofs on sunny days (Figs. 14 and 15).

However, during the evening, the black-shingled roofs also

tended to lose heat faster than did the white-shingled roofs.

In obtaining equilibrium with ambient outdoor temperature,

both black-shingled and white-shingled roofs generally experienced similar nighttime temperature profiles. Also, note

that on average over the 3-year monitoring period, the plywood of the black-shingled roof systems was annually subject to about 191 h of exposure to 120°F–130°F (49°C–

54°C), 116 h of 130°F–140°F (54°C–60°C), 46 h of 140°F–

150°F (60°C–66°C), 8 h of 150°F–160°F (66°C–71°C), and

2 h above 160°F (71°C) (Tables 1–3). Meanwhile, the

white-shingled roofs were annually subject to about 63 h of

exposure to 120°F–130°F (49°C–54°C), 9 h of 130°F–

140°F (54°C–60°C), and 2 h of 140°F–150°F (60°C–66°C)

(Tables 4–6).

Two points are apparent. First, shingle color or, more

appropriately, radiant absorptivity of the shingle was a

predominant factor in dictating peak roof sheathing temperatures. Second, the cumulative histograms of top-of-plywood

sheathing temperature (Figs. 6–11) consistently show a

saddle between 90°F (32°C) and 120°F (49°C), which may

represent the transition from ambient to radiant heating/cooling.

Difference in Yearly

Temperature Histories

A comparison of outdoor temperature histories from 1991

through 1994 is informative (Figs. 6–11, Tables 1–6).

When studying the winter weather/exposure patterns, note

that based on a comparison of the colder periods of outside

ambient temperature, the winters of 1991–92 and 1992–93

were quite similar in cumulative and minimum cold temperatures (Tables 1–6). Both of these winters were considered average to slightly colder than average. However, the

winter of 1993–94 was considerably colder than normal,

which became apparent when comparing the 3-year data.

We also noted that the effect of snow cover could often be

evaluated by simply monitoring the top-of-plywood temperatures. When snow cover was present, especially a new

snow cover on a previously snow-free roof with either

black- or white-shingled chambers, we repeatedly observed

that the top-of-plywood temperature data would hover very

near 32°F (0°C). We assume that as snow melts and refreezes, it acts as a phase-changing medium that stabilizes

the sheathing temperatures. Most importantly, we noted

that trends and/or fluctuations in this top-of-plywood temperature were controlled during snow-covered periods by the

air temperature in the interior attic space, which, in turn,

dictated the temperature at the bottom of the plywood

sheathing. In other words, the snow cover acted like an insulative blanket in which thermal loads on the roof sheathing were dictated from inside-to-outside heat flux rather than

the normal outside-to-inside flux.

Study of the summer temperature histories readily shows

that the summer of 1994, which was generally considered

average to slightly warmer than average, was much warmer

than either the previous summers (Figs. 6–11 and 13).

The summer of 1992 was considered cooler than normal

(Figs. 6 and 7), and the summer of 1993, considerably

cooler than normal (Figs. 8 and 9). In fact, during the

summer of 1993, we did not record an exterior temperature

above 89°F (32°C), and U.S. Weather Service records indicate that this summer was the second coolest summer recorded in Madison, Wisconsin, in the 20th century. Nevertheless, during the summers of 1992 and 1993, short warm

periods did occur (Fig. 14). In June of 1992, when exterior

temperatures exceeded 90°F (32°C) for several consecutive
7

Table 3—Temperatures in black-shingled exposure

chamber, October 1993–September 1994

Time (h) at given temperature at various locations

Temp Chamber Plywood

 ( ̊F) Inside Outside Top Bottom Rafter

−20 111 109 147 128 111

−10 156 219 164 169 167

0 277 329 284 261 268

10 561 572 646 622 572

20 834 872 805 832 827

30 1,413 1,531 1,373 1,382 1,374

40 994 1,073 921 956 970

50 1,119 1,178 1,079 1,138 1,100

60 1,290 1,596 1,058 1,141 1,234

70 796 970 581 701 773

80 574 279 406 489 543

90 422 31 305 398 455

100 178 — 303 327 286

110 21 — 246 171 69

120 2 — 218 41 10

130 — — 148 3 —

140 — — 60 — —

150 — — 13 — —

160 — — 2 — —

Table 4—Temperatures in white-shingled exposure

chamber, October 1991–September 1992

Time (h) at given temperature at various locations

Temp Chamber Plywood

 ( ̊F) Inside Outside Top Bottom Rafter

−20 8 — 16 11 11

−10 42 42 74 50 47

0 162 170 196 178 160

10 430 508 461 429 417

20 1,079 1,099 1,152 1,077 1,085

30 1,735 1,870 1,622 1,683 1,691

40 1,250 1,224 1,233 1,258 1,260

50 1,219 1,273 1,152 1,186 1,202

60 1,279 1,567 1,068 1,230 1,233

70 753 823 604 684 723

80 509 167 392 441 470

90 257 14 293 363 362

100 33 — 246 150 89

110 — — 178 17 7

120 — — 65 — —

130 — — 5 — —

140 — — — — —

150 — — — — —

160 — — — — —

Table 1—Temperatures in black-shingled exposure

chamber, October 1991–September 1992

Time (h) at given temperature at various locations

Temp Chamber Plywood

 ( ̊F)a Inside Outside Top Bottom Rafter

−20 9 — 15 12 14

−10 41 42 73 54 45

0 162 172 185 172 156

10 421 498 438 416 407

20 1,057 1,103 1,086 1,080 1,063

30 1,693 1,870 1,572 1,612 1,646

40 1,236 1,228 1,209 1,230 1,240

50 1,203 1,296 1,118 1,161 1,160

60 1,250 1,559 1,015 1,132 1,194

70 707 812 524 665 716

80 484 165 391 417 442

90 365 12 305 358 382

100 115 1 241 274 238

110 12 — 218 146 54

120 — — 194 28 —

130 — — 115 1 —

140 — — 52 — —

150 — — 6 — —

160 — — 1 — —

a

TC = (TF – 32)/1.8.

Table 2—Temperatures in black-shingled exposure

chamber, October 1992–September 1993

Time (h) at given temperature at various locations

Temp Chamber Plywood

 ( ̊F) Inside Outside Top Bottom Rafter

−20 4 1 10 7 6

−10 54 49 112 87 67

0 228 244 221 212 216

10 520 659 558 537 509

20 1,112 1,268 1,074 1,106 1,088

30 1,703 1,702 1,639 1,662 1,701

40 1,018 956 951 981 983

50 1,102 1,248 1,063 1,095 1,072

60 1,175 1,453 1043 1,116 1152

70 868 971 586 729 818

80 532 211 471 465 518

90 358 — 293 386 434

100 88 — 288 282 170

110 11 — 243 87 41

120 — — 162 25 5

130 — — 84 3 —

140 — — 27 — —

150 — — 6 — —

160 — — 3 — —
8

Table 5—Temperatures in white-shingled exposure

chamber, October 1992–September 1993

Time (h) at given temperature at various locations

Temp Chamber Plywood

 ( ̊F) Inside Outside Top Bottom Rafter

−20 4 1 11 6 6

−10 53 50 116 75 65

0 222 239 223 220 215

10 532 665 586 528 522

20 1,158 1,276 1,131 1,144 1,131

30 1,719 1,701 1,705 1,695 1,714

40 1,004 961 958 1,011 995

50 1,129 1,227 1,112 1,123 1,115

60 1,249 1,463 1,080 1,155 1,187

70 877 970 669 820 875

80 547 227 385 504 541

90 238 — 346 367 326

100 43 — 279 108 78

110 — — 126 23 10

120 — — 40 1 —

130 — — 10 — —

140 — — 3 — —

150 — — — — —

160 — — — — —

Table 6—Temperatures in white-shingled exposure

chamber, October 1993–September 1994

Time (h) at given temperature at various locations

Temp Chamber Plywood

 ( ̊F) Inside Outside Top Bottom Rafter

−20 110 111 152 119 112

−10 160 216 167 168 166

0 275 317 317 279 277

10 577 582 658 594 577

20 853 878 859 867 860

30 1,426 1,523 1,405 1,407 1,403

40 1,015 1,065 950 974 980

50 1,155 1,187 1,138 1,150 1,161

60 1,315 1,576 1,110 1,238 1,257

70 843 992 621 776 832

80 608 282 427 516 557

90 354 30 338 413 405

100 58 — 308 224 158

110 2 — 211 32 13

120 — — 84 2 1

130 — — 12 — —

140 — — 2 — —

150 — — — — —

160 — — — — —

days and afternoon wind speed at Truax Field in Madison

was reported at 5–10 mi/h (8–16 km/h), the white-shingled

chamber reached its maximum temperatures when rafter

temperatures exceeded 110°F (43°C) and top plywood temperature exceeded 135°F (57°C) (Fig. 14, Table 5). During

the same week in 1992, rafter temperatures in the blackshingled chamber approached 120°F (49°C) and the top

plywood temperature exceeded 150°F (66°C) (Fig. 14,

Table 2). However, that was not the maximum plywood

roof sheathing temperature for 1992. The peak happened a

few weeks later, during a 3-day period when daily exterior

temperatures only reached 85°F to 88°F (29°C to 31°C) but

Truax Field wind speed was ≤ 5 mi/h (≤ 8 km/h), at which

time the top plywood temperatures of the black-shingled

chamber exceeded 150°F (66°C) each day and reached their

annual maximum of 161°F (72°C) (Table 1). This indicates

that solar load and wind speed can be as important as outdoor temperature.

Temperature Trends

Over the 3-year monitoring period, the highest daily and

weekly temperatures were recorded in June 1994 after the

longest continuous hot-spell in Madison, Wisconsin—from

June 13 through June 26 (Fig. 15). During that period, the

sky was almost continuously clear from June 13–19 and

from June 21–22. Figure 15 reveals several temperature

trends.

First, note that from June 13 through June 17, daily high

temperatures peaked between 90° and 96°F (32°C and 36°C),

with warmest outside (shade) hourly temperatures recorded

on both June 16 and 17. The highest hourly temperature

over the 3-year period—168°F (77°C)—was recorded on

June 17 between 1:00 and 2:00 p.m. for the top surface of

the plywood roof sheathing of the black-shingled chamber.

The highest temperatures recorded at the bottom of the plywood sheathing and for the rafter were recorded 1 h later—

137°F (58°C) and 129°F (54°C), respectively. At that time

for the white-shingled chamber, the top surface of the plywood roof sheathing reached 147°F (64°C), the bottom of

the plywood sheathing 127°F (53°C), and the rafter 120°F

(49°C).

Second, note that on June 22, chamber temperatures were

nearly identical to the outside temperature of 60°F–70°F

(16°C–21°C) throughout the day as a result of continuous

rain.

Finally, note the modest drop in the mid-day recorded

temperatures on June 19 and again on June 23 and 24

caused by the brief occurrence of late-afternoon clouds and

light rain. This weather pattern was verified with U.S.

Weather Station records at Truax Field.
9

Note that there is a slow but consistent trend of rising daily

maximum temperatures for both black- and white-shingled

chambers. This trend could be explained in several ways.

One explanation could be as simple as diminishing wind

speed, which in turn results in less convective heat loss.

Another could be a slow reduction in upper atmosphere

cloud cover (high cirrus). Finally, the entire roof system

might be beginning to store energy. However, this last

possibility is unlikely because daily low temperatures do

not exhibit a corresponding trend of raising temperatures.

Overall it is interesting that the annual time–temperature

histories (Tables 1 to 6) are similar to the average number

of hours reported for similar ventilated and unventilated roof

structures (Rose 1992) and those predicted using roof temperature models (ASTM 1988, APA 1989). This confirms

that whereas internal attic air temperatures may be strongly

influenced by ventilation and insulation, the temperatures to

which roof-sheathing plywood and roof-truss lumber are

subjected appear to be primarily controlled by solar gain.

Thus, our decision to limit attic ventilation or attic insulation appears justified in regard to our objective of monitoring peak roof-sheathing temperatures and cumulative roofsheathing temperature histories. However, this result should

not be taken as counterindicative to the benefits of attic

ventilation in controlling attic air temperature, relative

humidity, and wood moisture content.

Concluding Remarks

The plywood roof sheathing of black-shingled field exposure chambers was subjected to significantly more time at

temperatures above 120 ̊F (49 ̊C) than the roof sheathing of

white-shingled chambers. On sunny days, the top ply of

plywood roof sheathing under black shingles was 10 ̊F to

15°F (5 ̊C to 8 ̊C) warmer than that of identical whiteshingled roof chambers. However, after dark, the blackshingled roof temperatures were similar to those of whiteshingled roofs. The maximum temperatures recorded in our

3-year study for black-shingled roofs were 168 ̊F (76 ̊C),

137 ̊F (58 ̊C), and 129 ̊F (54 ̊C) for the top ply, bottom

ply, and internal rafter temperatures, respectively. The

maximum temperatures recorded for the white-shingled

roofs were 147 ̊F (64 ̊C), 127 ̊F (53 ̊C), and 120 ̊F (49 ̊C)

for the top ply, bottom ply, and internal rafter temperatures,

respectively. The cumulative annual temperature histories

reported in this paper for unventilated and uninsulated roof

systems compared reasonably well with those reported for

similar sloped and shingled roof structures located in central

Illinois in which ventilation and insulation were specifically controlled. This confirms that the roof-sheathing plywood and roof-truss lumber temperatures, which are the

primary factors influencing thermal degrade of fire-retardanttreated materials, are primarily controlled by solar gain

rather than attic ventilation or attic insulation. However,

the effect of moisture content was not evaluated nor was

moisture controlled by attic ventilation.

References

AF&PA. 1991. National design specification for wood

construction. Washington, DC: American Forest and Paper

Association. 125 p.

APA. 1989. Fire-retardant-treated plywood: Prediction of

performance. Tacoma, WA: American Plywood Association.

ASTM. 1988. Effect of fire retardant treatments (FRT) on

the strength properties of wood. Minutes of a workshop;

1988 April 26; Madison, WI, sponsored by ASTM

D7.06.04 Section: Fire performance of wood. Madison, WI:

U.S. Department of Agriculture, Forest Service, Forest

Products Laboratory. 7 p.

Barnes, H.M. 1994. Historical perspective of fireretardants in AWPA. Appendix A. Report of AWPA

Subcommittee T9: Fire retardant treated commodities. In:

Proceedings, American Wood-Preservers’ Association. 88:

413–433.

Barnes, H.M.; Winandy, Jerrold E.; Conners,

T.E. 1993. Laboratory/field correlations for FRT plywood.

Competitive grant proposal for natural resources and the

environment. Grant No. 93-02444. Washington, DC:

USDA National Research Initiative.

Blackenstowe, D.E. 1987. Comparison of white versus

black surfaces for energy conservation. In: Proceedings, 8th

conference on roofing technology; 1987 April 16–17.

Gaithersburg, MD: National Bureau of Standards.

Catchpole, R.F. 1976. A thumbnail history of fireretardant treated wood and its acceptance by building codes.

In: Proceedings, American Wood-Preservers’ Association.

72: 152–156.

Davies, D.L. 1979. Formulating fire-retardants to

control moisture absorption by the treated wood. In:

Proceedings, American Wood-Preservers’ Association. 75:

96–101.

Heyer, Otto C. 1963. Study of temperature in wood

parts of houses throughout the United States. Res. Note

FPL–RN 012. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

Hunt, G.M.; Truax, T.R.; Harrison, C.A. 1930.

Fire resistance of wood treated with zinc chloride and

diammonium phosphate. In: Proceedings, American WoodPreservers’ Association. 26: 130–164.

Hunt, G.M.; Truax, T.R.; Harrison, C.A. 1931.

Additional experiments in fireproofing wood. In:

Proceedings, American Wood-Preservers’ Association. 27:

104–141.
10

Hunt, G.M.; Truax, T.R.; Harrison, C.A. 1932.

Experiments in fireproofing wood. 3d progress rep. In:

Proceedings, American Wood-Preservers’ Association. 28:

71–96.

Moreel, B. 1939. The Navy’s experience with the use of

treated wood. In: Proceedings, American Wood-Preservers’

Association. 35: 149–153.

NAHB. 1990. Home builders guide to fire retardant treated

plywood: Evaluation, testing, and replacement.

Washington, DC: National Research Center of the National

Association of Home Builders. 65 p.

NBS. 1979. Summer cooling and whole house ventilation.

NBS special pub. 548. Reppart, M.H., ed. Gaithersburg,

MD: National Bureau of Standards, U.S. Department of

Commerce,

Ozkan, E. 1993. Surface and inner temperature attainment

of flat roof systems in hot–dry climate. Saudi Arabia: King

Saud University, Riyadh.

Prince, R.E. 1915. Tests on the inflammability of

untreated wood and wood treated with fire-retarding

compounds. In: Proceedings, annual meeting, National

Fire Protection Association, Boston, MA.

Rose, W.B. 1992. Measured values of temperature and

sheathing moisture content in residential attic assemblies.

In: Geshwiler, M. (ed.). Thermal performance of the

exterior envelopes of building: Proceedings, ASHRAE/

DOE/BTECC conference; 1992 December 1–10; Clearwater

Beach, FL. Atlanta, GA: American Society of Heating,

Refrigerating, and Air-Conditioning Engineers: 379–390.

Rose, W.B. n.d. Temperature and sheathing moisture

content in residential attics. Unpub. rep. Champaign, IL:

Building Research Center, University of Illinois. Written in

1995.

TenWolde, Anton. 1988. Effect of fire retardant

treatments on strength properties of wood. Executive

summary of workshops. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory.

Truax, T.R.; Harrison, C.A.; Baechler, R.H.

1933. Experiments in fireproofing wood. 4th Progress Rep.

In: Proceedings, American Wood-Preservers’ Association.

29: 107–124.

Truax, T.R.; Harrison, C.A.; Baechler, R.H.

1935. Experiments in fireproofing wood. 5th Progress Rep.

In: Proceedings, American Wood-Preservers’ Association.

31: 231–248.

Wilkes, K.E. 1989. Model for roof thermal performance.

Oak Ridge National Laboratory Rep. ORNL/CON-274.

Oak Ridge, TN: Office of Scientific and Technical

Information.

1000

100

10

1

80 100 120 140 160 180

Exceedence temperature (°F)

Outside

Inside

Top ply

Bottom ply

Rafter

❋

❋

❋

❋ ❋ ❋ ❋ ❋

❋

✕

✕

✕✕

✕

✕

+

+

+

+ +

1992 Black

Hours/year

Figure 6—Number of hours that recorded

temperatures at specified locations went

beyond the exceedence temperature in

black-shingled exposure chamber in 1992.

Exceedence temperature is the range between some minimum temperature limit and

next higher exceedence temperature limit.

Outside and inside refer to exterior and interior temperatures of exposure chamber.

Top plywood and bottom ply refer to temperatures of plywood sheathing at respective places. a

TC = (TF – 32)/1.8.

1000

100

10

1

80 100 120 140 160 180

Exceedence temperature (°F)

Outside

Inside

Top ply

Bottom ply

❋ Rafter

❋

❋

❋

❋ ❋

❋

✕

✕

✕

+

+

+

+

1992 White

✕

✕

Hours/year

Figure 7—Number of hours that recorded

temperatures at specified locations went

beyond the exceedence temperature in

white-shingled exposure chamber in 1992.
11

1000

100

10

1

80 100 120 140 160 180

Exceedence temperature (°F)

Outside

Inside

Top ply

Bottom ply

Rafter

❋

❋

❋

❋

❋

❋

❋

❋

❋

✕

✕

✕

✕

✕

✕

+

+

+

+

1993 Black

❋ +

Hours/year

Figure 8—Number of hours that recorded

temperatures at specified locations went

beyond the exceedence temperature in

black-shingled exposure chamber in 1993.

1000

100

10

1

80 100 120 140 160 180

Exceedence temperature (°F)

Outside

Inside

Top ply

Bottom ply

Rafter

❋

❋

❋

❋

❋

❋ ❋

❋

✕

✕

✕

✕

✕ + +

+

+

1993 White

Hours/year

Figure 9—Number of hours that recorded

temperatures at specified locations went

beyond the exceedence temperature in

white-shingled exposure chamber in 1993.

1000

100

10

1

80 100 120 140 160 180

Exceedence temperature (°F)

Outside

Inside

Top ply

Bottom ply

Rafter

❋

❋

❋

❋

❋

❋ ❋

❋

✕

✕

✕

✕

✕

+

+

+

+

1994 Black

❋

❋ ✕+

+

Hours/year

Figure 10—Number of hours that recorded

temperatures at specified locations went

beyond the exceedence temperature in

black-shingled exposure chamber in 1994.

1000

100

10

1

80 100 120 140 160 180

Exceedence temperature (°F)

Outside

Inside

Top ply

Bottom ply

Rafter

❋

❋

❋

❋

❋

❋

❋

✕

✕

✕

✕

+

+

+

1994 White

❋

✕

+

+

✕

Hours/year

Figure 11—Number of hours that recorded

temperatures at specified locations went

beyond the exceedence temperature in

white-shingled exposure chamber in 1994.
12

Figure 12—Three-year averages for time that recorded temperatures at specified locations went beyond the exceedence temperature in black- and white-shingled exposure chambers.
13

Figure 13—Comparison of time that recorded temperatures at specified locations went beyond the exceedence temperature in black- and white-shingled exposure chambers in 1993 and 1994.
14Temperature (°F)

1992

1992

hottest

day

160

140

120

100

80

60

40

8 9 10 11 12 13 14

June

White rafter Black ply

Black rafter Outside

White ply

Figure 14—Comparison of temperature histories in specified locations in black- and

white-shingled exposure chambers in 1992. Temperature (°F)

1994

180

160

140

120

100

80

60

40

13 15 17 19 21 23 25

June

White rafter Black ply

Black rafter Outside

White ply

Hottest

day

Late-afternoon showers, 

then clearing

Rained

all day

Figure 15—Comparison of temperature histories in specified locations in black- and

white-shingled exposure chambers in 1994.