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Impact of Insulation Dimensional Stabilityon Conventional Roof Performance

Lorne Ricketts, Peng

and

Jun TataraRDH Building Science Inc.

224 W. 8th Avenue, Vancouver, BC, Canada Phone: 604-873-1181 • E-mail: [email protected] and [email protected]

3 3 r d r C I I n t e r n a t I o n a l C o n v e n t I o n a n d t r a d e S h o w • M a r C h 2 2 - 2 7 , 2 0 1 8 r I C k e t t S • 1 6 1

mailto:[email protected]:[email protected]

Abstract

Problems with creasing and ridging of styrene-butadiene-styrene (SBS) roof membranes in conventional roof assemblies have been observed in the field, along with stress concentrations and holes around fixed penetrations. Field observations have indicated that shrinkage of insulation products may put undue stress on the roof membranes and potentially affect overall durability. To investigate the potential effect of dimensional movement of insulation on the performance of SBS membranes, laboratory testing was performed on conventional roof specimens in a purpose-built climate chamber.

Speaker

Lorne Ricketts, Peng — RDH Building Science Inc.

LORNE RICKETTS is a building science engineer specializing in new construction, investigation, and research work at RDH Building Science Inc. His research work includes laboratory testing, field monitoring studies, product evaluation, hygrothermal and thermal modelling, and development of industry guidance documents. He has produced numerous published works and regularly presents at seminars and conferences throughout North America.

Nonpresenting Coauthor

Jun Tatara — RDH Building Science Inc.

1 6 2 • r I C k e t t S 3 3 r d r C I I n t e r n a t I o n a l C o n v e n t I o n a n d t r a d e S h o w • M a r C h 2 2 - 2 7 , 2 0 1 8

Impact of Insulation Dimensional Stabilityon Conventional Roof Performance

INTRODUC TION The thermal expansion and contraction

of insulation products within conventional roof assemblies has been identified as a potential performance concern in the roofing industry. This movement can create gaps between insulation boards, which can short-circuit the insulation with respect to heat flow. Problems with creasing and ridging of membranes have been observed in the field, along with stress concentrations and holes around fixed penetrations. In particular, preliminary field observations have indicated that shrinkage of expanded polystyrene (EPS) insulation products may put undue stress on the roof membranes and in conventional roof assemblies where the insulation also provides the substrate for the roofing membrane, and insulation movement could adversely affect the durability and integrity of styrene-butadiene-styrene (SBS) roof membranes and roofing systems. In the field, ridging of SBS roof membranes has been observed—even when EPS is used in accordance with relevant installation guidelines (National Roofing Contractors Association, 1982).

To investigate these industry concerns regarding the potential effect of dimensional movement of EPS insulation on the performance of SBS roof membranes, laboratory testing was performed on conventional roof specimens in a purpose-built climate chamber.

Two-ply SBS conventional roof specimens constructed with EPS insulation have shown significantly more movement at the insulation joint as compared to other insulation types (mineral wool and polyiso), as well as visual damage to the SBS roof membrane when exposed to uniform temperature on all sides of the roof specimens (Tatara & Ricketts, 2017). The focus of this paper was to investigate whether the top insulation layer of a stone wool-expanded polystyrene (SW/EPS) hybrid roof specimen could:

roof specimen, and • Provide a more thermally stable sub

strate for the protection board and the SBS roof membrane to minimize potential risk associated with use of EPS insulation as substrate for SBS roof membrane and protection board.

The results and analysis presented in this paper form a portion of the work performed as part of a larger study (Tatara & Ricketts, 2017) assessing other factors impacting the performance of two-ply SBS conventional roof systems.

It is important to note that the investigation described in this paper focuses on the potential for the thermal movement of insulation products to create wrinkles in roof membranes similar to wrinkles observed in the field, and represents an interim report of findings to date. While previous labo ratory findings combined with anecdotal field experience indicate this mechanism is a promising candidate for the cause of observed wrinkles in the field, this has not yet been confirmed and is part of ongoing investigation. Other potential causes may include membrane insulation securement method, quality of installation, and climate. Field investigations, roof performance monitoring, and further laboratory testing are ongoing to investigate this thermal movement of insulation products as a poten-

Exterior Mechanically Fastened EPS-Only Roof Specimen

tial mechanism, as well as other potential mechanisms.

ME THODOLO GY This section provides an overview of roof

specimen selection, climate chamber and instrumentation, test procedure, and interpretation of displacement measurements.

Roof Specimen Selection Several roof specimens were tested as

part of a larger study (Tatara & Ricketts, 2017); however, the results and analysis presented in this paper are of two mechanically fastened conventional roof systems that are identical in arrangement except that one incorporated 102 mm (4 in.) of EPS insulation while the other incorporated 51 mm (2 in.) of SW over 51 mm (2 in.) of EPS. A summary of the assemblies is provided in Tabl e 1.

The test specimens of each roof assembly, approximately 1220 x 2440 mm (4 x 8 ft.), were constructed by a certified roofer intimately familiar with roofing products and installation techniques. Each roof specimen was constructed such that there was a continuous joint in the middle of the insulation layer perpendicular to the length of the specimen. This joint separates the insulation into two separate halves. The protection board and roof membrane were installed continuously across the insulation joint. During construction of the roof

Mechanically FastenedSW/EPS Hybrid

Roof Specimen

SBS Cap Sheet (Nonwoven Polyester Reinforced)

SBS Base Sheet (Nonwoven Polyester Reinforced)

4.8mm (3/16 in.) Protection Board (Glass Matt Reinforced)

51 mm (2 in.) SW 102 mm (4 in.) EPS

51 mm (2 in.) EPS

Self-Adhered Vapor Barrier

• Thermally protect the potentially 13 mm (½ in.) Plywoodtemperature-sensitive EPS insula- Interior 38 mm by 89 mm (2x4) Framing tion from the temperature extremes

experienced at the top surface of the Table 1 – Summary of roof specimens.


Figure 1 – Underside of roof specimen displacement sensors (yellow dashed circles) were installed

post-construction from the underside of the roof specimen at the insulation joint (red dashed line).

Figure 2 – Test chamber arrangement for testing roof specimens with temperature gradient. Note that testing chamber was separated into two parts: where heating and cooling took place (shaded in red) and where it was kept at room temperature (22°C or 71.6°F, shaded in blue). SW/EPS hybrid roof specimen shown, outlined in red dotted line.

Figure 3 – Temperature sensor location within the roof specimen (SW/EPS hybrid roof specimen shown.)

specimens, the insulation boards were butted together, per typical construction practices. Additionally, a gap was created between the plywood sheets, including the self-adhesive vapor barrier, aligned with the joint in the insulation to facilitate sensor installation, as shown in Figure 1.

Climate Chamber and Instrumentation

The roof specimens were exposed to both cold (-15°C, 5°F) and hot (~90°C, ~194°F) temperatures using a custom-built climate chamber. In order to test the roof specimens with a temperature gradient

across the assembly, which is similar to in-service conditions experienced by roofs, the test chamber wall was modified such that room temperature air (~22°C, ~71.6°F) could be circulated under the specimen, while the space above the roof (in the climate chamber) could be cooled or heated. The space around the roof specimen was insulated as a guard to protect the edges of the roof specimen from being

exposed too directly to the climate chamber and to ensure that an even temperature difference was experienced by the specimen. The arrange ment of a roof specimen in the chamber is shown in Figure 2.

A total of eight temperature sensors were used to measure the temperature at key layers in each half of the roof specimen (four sensors per half ) as shown in Figure 3. These sensors were installed along the center of the 1220- by 1220-mm (4- by 4-ft.) insulation boards during the construction of the roof specimen, except for the temperature sensors installed at the surface of the SBS roof membrane, and sensors installed at mid-height of the 102-mm (4-in.) EPS insulation boards, which were installed after the roof specimens were constructed.


Four additional temperature sensors were installed to monitor ambient temperature inside the climate chamber (near the cooling and heating source, above the roof spec imen, and two below the roof specimen).

The movement at the insulation joint was measured using four plunger-type displacement sensors approximately 305 mm (1 ft.) from either side of the roof specimen. Two sensors were installed in each insulation layer, or two in each of the top and bottom halves of 102-mm (4-in.) EPS insulation boards as shown in Figure 4.

Test Procedure Roof monitoring data from an ongoing

field monitoring study of a large roof on an industrial building in Chilliwack, within the Lower Mainland of British Columbia, were extracted. The data from a four-year monitoring period (2013 to 2016) revealed that in a typical year, cap sheet temperatures of the black SBS roof membrane experienced approximately 102 hours of temperature above 70°C (158°F) and approximately five hours above 80°C (176°F). One of the highest temperatures was recorded June 30, 2013; and temperatures at the SBS surface (black cap sheet), above the insulation (polyiso), below the insulation, and interior air temperature are plotted in Figure 5. These extracted monitoring data were used to help determine the temperature profile for the heating cycle in this laboratory testing. As the roof temperature is largely dependent on solar heating of the roof surface, the measured roof temperature at this study building is likely to be similar to that for many other roofs with the same membrane reflec tance. Latitude, ambient air temperature, wind, shading by neighboring buildings, and cloud cover may impact the temperature of other comparable roofs.

The coldest temperature experienced by a roof surface will be highly cli-mate-dependent; therefore, a similar analysis of the Chilliwack test data was not completed to determine the coldest surface temperature. Instead, a set amount of dry ice was used to cool the SBS roof membrane surface temperature to approximately -10°C (14°F).

Each roof specimen was

Figure 4 – Plunger type displacement sensors installed in top/bottom halves of 10- mm (4-in.) EPS insulation board for EPS-only roof specimen (left) and in each insulation layer for SW/EPS hybrid insulation roof specimen (right).

Figure 5 – SBS roof membrane surface (black cap sheet) temperature; temperature above and under insulation (polyiso) and interior air temperature between 2013-06-30 00:00 to 2013-07-01 00:00 obtained from an ongoing field monitoring study of a large roof on an industrial building in Chilliwack, BC.

Figure 6 – Testing chamber setup for a cooling cycle. Cooling test was performed with dry ice placed over a partial temperature shroud.


Figure 7 – Typical cooling cycle. Average of two sensors at 30 minutes (EPS-only roof specimen shown).

Figure 8 – Testing chamber setup for

a heating cycle. Aluminum foil shroud

was used to avoid direct infrared exposure of the SBS roof membrane.

Figure 9 – Typical heating cycle. Average of two sensors at 30 minutes(SW/EPS hybrid roof specimen shown).

installed in the climate chamber and left undisturbed for 24 hours. After this time, the cooling cycle was performed with dry ice placed over a partial temperature shroud (Figure 6 ).

The temperature at key points through the roof specimen during a typical cooling cycle is plotted in Figure 7.

As shown in the cooling cycle temperature plot, the specimen was allowed to return to equilibrium temperature before the heating cycle was started. The heating cycle (Figure 8) was performed until the SBS surface temperature reached 90°C (164°F) and held for four hours, then allowed to return to equilibrium temperature before the heating cycle was repeated for a minimum of two cycles (the heating cycle was repeated three times on the EPS-only roof specimen) to simulate cyclic exposure due

to solar radiation exposure of the SBS roof membrane.

To avoid uneven surface temperature gradients during the heating cycle, the temperature set point was increased incrementally to 50°C (122°F), 70°C (158°F), and then to 90°C (164°F). Air circulation fans (not clearly visible in the photo) were used to keep an even temperature within the chamber above the SBS roof membrane surface. Additionally, aluminum foil was used as a shroud on the heat lamps to avoid direct infrared exposure of the SBS roof membrane. The temperature at points in a roof specimen during a typical heating cycle is plotted in Figure 9.


The testing was considered complete when the roof specimen returned to equilib rium laboratory temperature (22°C, 71.6°F)) after the heating cycles. When testing was complete, roof specimens were inspected and disassembled to allow visual and physi cal observations.

Note that the cooling and the heating tests were not time-dependent except that the SBS roof membrane surface temperature was held for approximately four hours during each heating cycle. The overall duration of the test varied for each roof specimen

as a result of a difference in the thermal mass of the specimens (mineral wool insulation has much higher thermal mass than does the EPS, so these specimens were typically exposed to test conditions for a longer period of time).

Interpretation of Displacement Measurement

One of the key measurements was taken with displacement sensors installed between insulation boards. This section provides a summary of how the displace

ment sensor measurements will be interpreted and possible causes of this move ment since these measurements could be misunderstood as dimensional change in insulation boards when, in some cases, other movements also impact the measurements. In this paper, these displacement measurements will be interpreted as changes in the distance between the insulation boards (i.e., gap width), as that is what the sensors directly measure. Interpretation of measurements is provided as a summary in Tabl e 2 . The arrows in this table indicate

Rapid and significant increase in the gap width

SBS roof membrane expands and pulls insulation boards

away from each other while insulation

contracts/shrinks.

Increase in the gap width

SBS roof membrane expands and pulls insulation boards away from each other. The rate of expansion of SBS roof membrane is greater than the rate of expansion of insulation.

Insulation contracts/shrinks and widens the gap. The rate of contraction/shrinkage of the SBS roof membrane is smaller than the rate of contraction/ shrinkage of the insulation.

Decrease in the gap width

Insulation expands and narrows the gap. The rate of expansion of SBS is smaller than the rate of expansion of insulation.

SBS roof membrane contracts/shrinks and pulls insulation boards closer together. The rate of contraction/ shrinkage of SBS is greater than the rate of contraction/ shrinkage of insulation.

Rapid and significant decrease in the gap width

SBS roof membrane contracts/shrinks and pulls insulation

boards closer together while

insulation expands.

Table 2 – Summary of movements at the insulation joint.


Figure 10 – Graph comparing temperature at SBS surface, above EPS insulation, center (mid-height) of EPS insulation, and under EPS insulation and change in gap width of EPS only roof specimen during cooling cycle.

the direction of movement, and the size of the arrows indicates the relative rate or the magnitude of movement (i.e., the larger the arrow, the greater the movement). The color of the arrows indicates thermal expansion in red and thermal contraction or shrinkage of material in blue.

Note that the main cause of dimensional change in wood products is due to its moisture content. The expansion and contraction of wood products due to temperature is much smaller in comparison. It is unlikely that thermal expansion and contraction of wood material in the roof specimen significantly influenced displacement sensor measurements, and therefore it is not considered in the summary of movements provided.

The displacement sensor used in this testing has a total mechanical travel of 14.2 mm ±0.38 mm (0.56 in. ±0.015 in.) (RS-1114, Rev. B). The best effort was made to install the sensors in the same location relative to the insulation joint; however, the actual installation location determined the allowable sensor plunger travel distance and, consequently, the upper measurable limit of the gap width. Additionally, the intention was to construct the roof specimens with butted insulation joints with no gaps; however, any existing construction gap and its width impacted the lower displacement limit.

RESULTS AND DISCUSSION This section contains the result and dis

cussion of two mechanically fastened roof specimens: one with 102 mm (4 in.) of EPS

insulation and the other with 51 mm (2 in.) of SW insulation over 51 mm (2 in.) of EPS insulation.

In the larger study (Tatara and Ricketts, 2017), roof specimens with EPS insulation have shown significantly more movement at the insulation joint with visual damage to the SBS roof membrane when exposed to uniform heat on all sides of the roof specimens. This initial testing was done to simulate a worst-case scenario to quickly determine a boundary on the problem and establish whether thermal movement of materials within the roof assembly could, in fact, create wrinkles similar to those observed in the field. This initial testing was able to create wrinkles in some assemblies with EPS insulation, including an assembly identical to the EPS-insulated roof assem

bly described in this paper (but tested with uniform exposure to heat).

This subsequent round of testing is intended to expose the specimen to conditions more similar to those experienced in the field where a temperature gradient exists through the thickness of the roof assembly. Using this testing arrangement, the SW/EPS hybrid roof specimen was tested to investigate whether the top insulation layer in the roof specimen can provide the dual purpose of thermally protecting the potentially sensitive EPS insulation so that it does not experience the temperature extremes present at the top surface of the roof specimen, and also to provide a more thermally stable substrate for protec tion board and the SBS roof membrane to minimize potential impact of the substrate (insulation) on the performance of the membrane.

Mechanically Fastened EPS-Only Roof Specimen

The graph in F ig ure 10 indicates temperature of the EPS-only roof specimen at key locations through the roof assembly (SBS surface, above EPS insulation, center of insulation, and under EPS insulation) and changes in gap width at the top and bottom half of the insulation joints (25 and 76 mm or 1 and 3 in. from the top, respec tively) during the cooling cycle. Note that the EPS insulation incorporated in this specimen has a board thickness of 102 mm (4 in.), which is unlike the SW/EPS hybrid system in which two different insulation layers—each 51 mm (2 in.) thick—create a total insulation layer thickness of 102 mm

Figure 11 – Graph comparing temperature at key locations through the assembly

and change in gap width of EPS-only roof specimen during the first heating cycle.


(4 in.). The data provided here are analyzed and plotted at a moving average of 30 minutes (six readings) of two sensors to filter out sensor noise.

The temperature plots illustrate a clear temperature gradient across the roof specimen during the cooling cycle, which is similar to what the roof would be expected to experience during colder winter months. While the SBS roof membrane surface temperature fell to just below -10°C (14°F), the bottom surface of the specimen was near the roof temperature (22°C, 71.6°F). As expected, the plots for the changes in gap width illustrate that the gap widened as the roof specimen was cooled, likely correlating with thermal contraction of the EPS layer. It is interesting to note that although one layer of EPS insulation board at 102-mm (4-in.) thickness was used instead of two layers of 51-mm (2-in.) boards, the figure shows a difference in magnitude of thermal contraction between the top and bottom half of the same insulation boards, with significantly more movement measured in the top half of the insulation boards.

The graph provided in F i g u r e 11 compares the temperature of the same roof specimen at the same key locations and changes in gap width at the top and bottom half of the insulation joints during the first heating cycle. Note that the data provided here are analyzed and plotted at a moving average of 30 minutes (six readings) of two sensors to filter out sensor noise.

Once again, the temperature plots illustrate a clear temperature gradient across the roof specimen during the heating cycle, which is similar to what the roof would be expected to experience in the hot summer months. While the SBS roof membrane surface temperature was raised to 90°C (164°F) for approximately four hours (a notably extreme condition), the underside of the EPS insulation was maintained at a temperature below approximately 35°C (95°F), and thus was not exposed to the extreme hot temperature.

As expected, the plots for the changes in gap width illustrate that the gap narrowed as the roof specimen was heated up to approximately 70°C (158°F), corresponding with predicted thermal expansion of the insulation boards. Upon closer inspection, the gap between insulation boards measured at 25 mm (1 in.) from the top of insulation narrowed up to approximately 1.0 mm (0.039 in.) when the top surface of the

insulation reached 68°C (154.4°F). However, narrowing of the gap appears to have been limited by the insulation boards coming in contact, preventing further expansion of the insulation.

Upon cooling of the specimen after the heating cycle, a gap of approximately 2.14 mm (0.084 in.) was formed, indicating that while not measurable due to contact of the boards, the insulation did experience some permanent shrinkage as a result of the exposure to heat. Similar to the measured change in gap width during the cooling cycle, the figure shows a different magnitude of dimensional movement in the top half of the insulation as compared to the bottom half. This finding is consistent with what one would expect as a result of the temperature gradient created across the roof specimen.

After this initial round of testing, no wrinkling of the roof membrane was observed, and the movement of the insulation was less than that measured with the similarly assembled EPS-only roof speci men tested in uniform temperature as part of the larger study (Tatara and Ricketts, 2017) in which wrinkling was observed.

To assess whether repeated or prolonged exposure can increase the change in gap width between insulation boards, the roof specimen was exposed to the heating cycle two more times. This type of cyclic exposure is consistent with in-service exposure to diurnal temperature and solar exposure conditions often experienced by roofs in-service.

Figure 12 – Graph comparing temperature at key locations through the assembly and change in gap width of EPS-only roof specimen during heating cycles. Note that the gap in the plot between the first and the second heating cycle is due to data loss. Additionally, small temperature spikes are due to malfunctioning of digital temperature switch.

F i g u re 12 provides the temperature and corresponding changes in gap width at the same key locations as in F i g ur e 1, but includes two subsequent heating cycles. Additionally, in some cases, small temperature spikes occurred as a result of malfunctioning of the controls. These are not thought to have significantly impacted the overall results.

While the general trend in each heating cycle is similar, each cycle of heating the EPS-only roof specimen created a permanent increase in the gap width between insulation boards. It is theorized that this gap is the result of plastic deformation of EPS insulation when heated above 80°C (176°F) and/or of damage to the insula tion from contact during thermal expansion, in which case repeated heating may be causing increased damage on each cycle, resulting in the observed increase in gap width. Further investigation, including additional heating cycles, would be neces sary to confirm this trend and evaluate whether a maximum gap size is reached, as well as whether it can potentially cause wrinkling.

F i g ure 13 plots the gap width between the top half and the bottom half of 102-mm (4-in.) EPS insulation boards in the EPS-only roof specimen during the first heating cycle as a function of insulation temperature. Note that the initial gap width is highlighted in a black bold horizontal line, and initial/room temperature is indicated by a red dotted vertical line.


Figure 13 – Gap width between the top half and the bottom half of 10- mm (4-in.) EPS insulation boards in EPS-only roof specimen during the first heating cycle plotted as a function of insulation temperature.

As illustrated in the figure, the top half of the 102-mm (4-in.) EPS insulation board moved slightly more than the bottom half, and this is due to temperature gradient across the insulation. The top half of the insulation was subject to higher temperatures, and the effect of thermal expansion was greater.

Typically, thermal expansion and contraction of material is proportional to change in temperature, and the relationship between the change in dimension and the change in temperature is typically linear when plotted, unless the material undergoes some other type of physical change. In particular, previous testing has shown that EPS can experience permanent shrinkage, and it does

Figure 14 – Gap width between the top half of 102-mm (4-in.) EPS insulation boards in

EPS-only roof specimen during the first, second, and third heating cycle plotted as a

function of insulation temperature.

so at approximately 80°C or 176°F (Bowden, Ricketts, and Finch, 2015). The observed permanent change in gap width may be a result of this shrinkage at high temperatures, or could potentially be a result of damage to the insulation boards due to contact as they expanded during heating.

F i g u r e 14 plots the gap width between the top half of the 102-mm (4-in.) EPS insulation boards in the EPS-only roof specimen during the first, second, and third heating cycle as a function of insulation temperature. This plot clearly indicates that while the change in gap width is greatest in the first cycle, subsequent heating cycles continues to increase the width of the gap between EPS

Figure 15 – Photos taken during sensor installation before the test (left) and after the test (right). Note that the insulation boards are butted tight and virtually no gap was present before the test; however, after the test, the gap is clearly wider closer to the top of the roof assembly and there is slight lifting at bottom corners.


Figure 16 – Photos of one of the EPS insulation boards taken after cooling and heating cycles. Note that slight upward cupping approximately 8 mm (0.315 in.) from the horizontal was observed on the bottom surface.

insulation boards. Once the roof specimen was allowed to

cool down to 22°C (71.6°F) after the heating cycles, it was disassembled to make visual and physical observations. Upon visual inspection, no ridging or wrinkling of the SBS roof membrane was observed. Before and after photos taken at the same insulation joint provided in F i g ur e 15 confirm permanent widening of the gap between the insulation boards, and it is evident that the gap is wider closer to the top of the assembly, consistent with the measurements.

The fasteners were carefully removed to allow for observation of the insulation boards. The fastener heads were readily apparent through the rough membrane due to slight bulging of the membrane at the fastener head locations. Using a straight edge for comparison, it became evident that the EPS insulation boards had bowed as a result of the testing. The insulation board experienced a slight upward cup ping approximately 8 mm (0.315 in.) from horizontal at the bottom as shown in F i g ure 16 in both machine direction and cross-machine direction (length and width) of the insulation board. A similar measurement was made on the top surface of the insulation board and confirmed the noted cupping of the insulation board.

Cupping of a material often indicates differential expansion or contraction of one side of the material. In this case, cupping is consistent with shrinkage of the top layer of the EPS insulation as a result of exposure to the most extreme temperature. Overall,

while no wrinkling or significant damage to the SBS roof membrane was noted in the EPS roof specimen, cyclic testing of the specimen indicates a potential “ratcheting” effect by which more permanent deformation of the insulation boards occurs each time it is exposed to a heating cycle. Further work is required to fully investigate the cause and impact of this potential effect.

Mechanically Fastened SW/EPS Hybrid Roof Specimen

With the SW/EPS hybrid roof specimen, the stone wool insulation layer provides both a thermally stable substrate and also insulates the EPS from extreme tempera-

Figure 17 – Graph comparing temperature at key locations through the assembly and change in gap width of SW/EPS hybrid roof specimen during cooling cycle. Note that unusually high temperature under EPS insulation is due to heating system where testing chamber was located.

tures during testing. It is anticipated that using this arrangement to separate the EPS from the roof membrane and protect it from extreme temperatures may provide a practical method to use EPS insulation in roof assemblies while limiting its dimensional movement and potential impact on the performance of the assembly.

The graph provided in F i g u r e 17 indicates the temperature of the SW/EPS hybrid roof specimen at key locations through the assembly (SBS surface, above the top SW insulation layer, between SW/EPS insulation layers, and under the bottom EPS insulation layer) and changes in gap width at the top (SW) and the bottom (EPS) insu


Figure 18 – Graph comparing temperature at key locations through the assembly and change in gap width of SW/EPS hybrid roof specimen during heating cycle. Note that unusually high/low temperature under EPS insulation is due to heating system where testing chamber was located. Additionally, small temperature spike is due to malfunctioning of digital temperature switch, and a larger increase in temperature between the first and the second heating cycle was an attempt to start the second heating cycle, which we later decided to postpone.

lation joints during the cooling cycle. Note that, similar to previous data, the data provided here are analyzed and plotted at a moving average of 30 minutes (six readings) of two sensors to filter out sensor noise. Additionally, the unusually high temperature under the roof specimen during this testing was unintentionally caused by the building heating system being in close proximity to the test chamber.

Typically, the joint between EPS insulation boards has been measured to widen during a cooling cycle; however, no significant movement was observed at the insulation joint for this specimen during the cooling cycle. This is likely due to the EPS insulation being thermally protected by the top SW insulation layer and not being exposed to cold temperature on the surface of the specimen. There is actually a slight decrease in the gap width between the SW insulation boards, which is potentially attributable to slight thermal contraction of the SBS roof membrane that spans the joint.

The graph provided in F i g ure 18 indicates the temperature of the SW/ EPS hybrid roof specimen at the same key locations and changes in gap width at the top and the bottom insulation joints during the whole heating cycle (two heating cycles). Note that the data provided here are analyzed

and plotted at a moving average of 30 minutes (six readings) of two sensors to filter out sensor noise. Additionally, unusually high/ low temperatures under the roof specimen are due to the unintentional close proximity of a heating system, and a small temperature spike is due to a malfunctioning digital temperature switch. A larger increase in temperature between the first and the sec ond heating cycle was an attempt to start the second heating cycle, which was then later postponed. These are not thought to meaningfully impact the results.

This figure shows slightly more move-

Figure 19 – Gap width between the top layer (SW) and the bottom layer (EPS) of insulation boards in SW/EPS hybrid roof specimen during the first heating cycle plotted as a function of insulation temperature.

ment in the bottom insulation layer (EPS) during the heating cycles than during the cooling cycle. The insulation joint in the bottom EPS insulation layer narrowed as the roof specimen temperature was increased, likely due to thermal expansion of EPS insulation. The narrowing of the gap was not permanent and returned to its original position after cooling of the specimen to roof temperature.

F i g u r e 19 plots gap width between the top layer (SW) and the bottom layer (EPS) of insulation boards in the SW/EPS hybrid roof specimen during the first heating cycle as a function of insulation temperature. As illustrated in the figure, both the SW insulation layer (top) and EPS insulation layer (bottom) experienced ver y small move ments when tested in this arrangement and returned to essentially the same position upon cooling.

Overall, the movement within the assembly in each of the first and the second cycles was similar, with no notable difference in the gap width after each cycle. This suggests that the stone wool insulation board was successful in maintaining the EPS insulation at less extreme temperatures, and thus limited the potential for the permanent increase in gap widths between the insulation boards.

Once the roof specimen was allowed to cool down to 22°C (71.6°F) after the heating cycles, it was disassembled to make visual and physical observations. Visual and physical inspection revealed no ridging and wrinkling of the SBS roof membrane and no permanent deformation of insulation boards.


CONCLUSIONS The objective of this testing was to

evaluate the performance of roof specimens incorporating EPS insulation in different arrangements when exposed to a temperature gradient from the top surface to the bottom surface, representing temperature exposure roofs may experience in service in order to investigate whether it was possible to reproduce wrinkles observed in the field when using this more realistic exposure arrangement as compared to previous testing of similar assemblies that were exposed to uniform temperature. Two similarly constructed roof specimens—one with only EPS insulation and the other with a SW and EPS hybrid insulation arrangements—were tested. This study found that:

• No significant permanent movement of or damage to the roof specimens was noted due to exposure to cold temperatures.

• No visual damage of the SBS roof membrane was observed in either of the roof specimens tested (except for minor bulging of the fastener heads in the EPS roof specimen), although the surface of the SBS roof membrane was subjected to similar condition as roof specimens tested in uniform temperature conditions as part of the larger study (Tatara and Ricketts, 2017). This is likely due to the insulation layer(s) expe

riencing significantly less extreme temperatures through its thickness as compared to the previous testing.

• Permanent shrinkage of EPS insulation was observed in the mechanically fastened EPS-only roof specimen closer to the top of the assembly where the insulation experienced temperatures above 80°C (176°F). Additionally, the gap between the insulation boards continued to widen on each of three heating cycles. Further testing is recommended to evaluate whether extended duration or repeated exposure would continue to gradually increase the gap width between insulation boards and potentially damage the SBS roof membrane.

• 51 mm (2 in.) of SW insulation installed above 51 mm (2 in.) of EPS insulation protected the EPS insulation from the extreme temperature conditions experienced by the SBS roof membrane surface and the upper portion of the insulation. This resulted in limited dimensional movement of the insulation in this assembly.

Overall, the findings of this work have not confirmed that EPS movement is the cause of wrinkles observed in the field; however, given the obser ved ratcheting

of the insulation causing an increasing change in the gap width upon subsequent heating cycles, it is possible that this mechanism may result in wrinkling over time. This, in fact, could potentially correlate with the delayed wrinkling of some roofs that is observed in the field. It is also important to note that this investigation looked at only one potential cause, and that field investigations performed after this testing was completed have also pointed towards other contributing or causal factors such as quality of the installa tion, method of insulation and membrane securement, and climate. Further inves tigation is underway in the field and the laborator y to continue to develop the body of knowledge in this area.

REFERENCES A. Bowden, L. Ricketts, and G. Finch.

Dimensional Stability of Rigid Board Insulation Products. 2015.

National Roofing Contractors Association. “NRCA Statement of Expanded Polystyrene Roof Insulation (EPS).” Technical Developments Bulletin #12. August 1982.

SMT Research Ltd. RS-1114, Rev. B. (n.d.). Basic Displacement Sensor Datasheet.

J. Tatara and L. Ricketts. Impact of Material Dimensional Stability on Conventional Roof Performance. 2017.


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