Good Codes Vs. Durable Roofs – Which Is the Missing Link? Where Is the Sweet Spot?

Good Codes vs. Durable Roofs –
Which Is the Missing Link?
Where Is the Sweet Spot?
Bas Baskaran, PhD, PEng;
Dominique Lefebvre;
Mauricio Chavez, PhD;
and
Sudhakar Molleti, PhD
National Research Council of Canada
1200 Montreal Road, Ottawa, ON, K1A 0R6 Canada
Phone: 613-990-3616 • E-mail: bas.baskaran@nrc.ca
RC 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 ow • Ma rc h 1 4 – 1 9 , 2 0 1 9 B a sk a r a n a n d L e f e b v r e • 6 3
Keywords
Climate adaptation, wind, thermal, watertightness, roofs, field testing, code compliance
Abstract
Recent frequent occurrences of extreme weather events threaten the performance of the roof assembly in two ways. The first is damage from extreme and sudden catastrophic events (hurricanes, wildfires, floods, tornados, etc.). The second is from recurring elevated stress over a relatively long period of time. The latter would include more frequent heat waves, droughts, and overall increases in rain, and higher sustained winds. When exposed to these extreme weather elements, the durability of low-slope membrane roofs (LSMRs) depends on three factors:
1) Good design based on updated code provisions
2) Systematic lab evaluation that closely mimics the weather elements
3) Quality installation with evaluated roofing components
The National Research Council of Canada (NRC), as part of the Canadian climate adaptation initiative, is carrying out a project: Guidelines for Commissioning and Certifying the Resiliency of Roofs Subjected to Extreme Weather Events, which aims to develop field protocols to assess in-situ roof conditions. There are no comprehensive guidelines to assess the capacity of existing roofs after weather events, nor to validate the designed capacity of newly installed roofs. The speaker will present the performance-based solutions to this missing link. This presentation focuses on additional requirements for climate adaptation that are applicable to climatic zones classified as “moderate” and “severe” for respective climatic loads. Requirements will be systematically presented for design and resistance estimation for components and systems through laboratory evaluations and field installation certification of the LSMR.
Speakers
Bas Baskaran, PhD, PEng – National Research Council Canada – Ottawa, Ontario
DR. BASKARAN is a group leader at NRC, where he is researching wind effects on building envelopes. As adjunct professor at the University of Ottawa, he supervises graduate students. As a professional engineer, he is a member of RICOWI, RCI, ASCE, SPRI, ICBEST, and CIB technical committees. He is a research advisor to various task groups of the National Building Code of Canada and a member of the wind load committee of ASCE. He has authored and/or coauthored over 200 research articles and received over 25 awards, including the Frank Lander Award from the Canadian Roofing Contractors Association and the Carl Cash Award from ASTM. Dr. Baskaran was recognized by Her Majesty Queen Elizabeth II with the Diamond Jubilee Medal for his contribution to his fellow Canadians.
Dominique Lefebvre – National Research Council Canada – Ottawa, Ontario
DOMINIQUE LEFEBVRE is a research officer at the NRC Canada, where her research focuses on the evaluation of the interface of various roofing materials, as well as the development of tools and techniques for climate adaptation of commercial roofs. At present, she is working on developing the performance requirements of cover boards in low-slope membrane roofing for the creation of a harmonized standard. She is registered with the Professional Engineers Ontario. Lefebvre has authored and/or coauthored research articles and was the recipient of several awards during her graduate and undergraduate studies at the University of Ottawa.
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INTRODUCTION
Consistent efforts are being put forth to modify the building code requirements and improve the built environment. The modifications that are implemented are aimed at increasing the resiliency of buildings. To achieve this, standards are created and modified for inclusion in the building code based on evolving requirements to improve current practices. However, through the analysis of existing buildings, it is evident that there is a missing link to the above conventional approach. Even if a designed resistance exceeds the load specifications in the building code, there are issues that are observed in the field that cannot be captured through only these two requirements. The National Research Council of Canada (NRC) hosted an industry consultation on building resiliency that included over 30 participants from various sectors of the roofing and insulation industries.1 During the consultation, the participants identified that an equally important requirement that is often overlooked is field installation. The quality of the installation has a significant impact on the performance of the installed system. Therefore, to achieve resiliency, all three requirements should be properly integrated, including the code specifications (load), the evaluation through testing (resistance), and the quality-controlled field applications (installation). Figure 1 illustrates that when the three requirements are combined, the “sweet spot” is achieved. This concept was presented at the 2018 convention,2 together with a summary of the industry consultation outcomes.
To verify the field installation requirements, evaluation is required on the installed system to confirm its performance. There is limited information available on how to accurately assess the capacity of an installed or existing roofing system. As such, the NRC formulated a project, Guidelines for Commissioning and Certifying the Resiliency of Roofs Subjected to Extreme Weather Events, to develop evaluation methodologies. Field protocols were developed to perform assessments of wind uplift resistance, thermal performance, and water-tightness. The tools developed will allow the industry to assess the capacity of a new roof to ensure that it can be installed to meet the design requirements and withstand climatic events. The methodologies can also be applied to existing roofs to assess the remaining capacity after either an extreme event or deterioration due to the exposure of weather elements. This paper refers to Canadian code requirements and Canadian field investigations. However, the holistic approach, shown in Figure 1, can be globally used, not only for roofs, but also for other building envelope systems.
WIND INVESTIGATION
The effect of wind on a commercial building can be highly variable. To better understand the field wind effects, a building was instrumented with wind speed and
Good Codes vs. Durable Roofs –
Which Is the Missing Link? Where Is the Sweet Spot?
RCI International Convention and Trade Show • MarcRCh 14-19, 2019 B BaSKaran and Lefebvre • 65
Figure 1 – Holistic approach for climate change adaptation of building envelopes.
Figure 2 – Sample of time history for wind speed and pressures.
pressure measuring devices. Measurements obtained are shown in Figure 2.3 From the 24-hour data, a 60-minute set (30 minutes before and 30 minutes after the wind peak) was extracted and plotted in Figure 2a. The recorded peak speed of 29.5 m.s-1 (66 mph) and calculated mean speed of 9.7 m.s-1 (22 mph) are presented. Areas with pressure taps are emphasized by colored squares in Figure 2b. The corresponding suction time histories for one pressure tap for each roof zone are shown in Figure 2c. The instantaneous negative peaks are 1150 Pa (24 psf), 480 Pa (10 psf), and 383 Pa (8 psf) for the corner, edge, and field, respectively. Note that the peak pressures do not occur at the same time as that of the wind. This is due to the delay in the response of the roof assembly. Two mean values, averaged over 60 minutes (mean 60) and 10 minutes (mean 10), are also shown for each zone. It was observed that taking the average over a longer period of time results in mean values that are lower in magnitude.
To simulate the field wind uplift forces, a protocol was developed using a Portable Wind Uplift Apparatus (PWUA), shown in Figure 3. The study by Canon et al. was used as a starting point.4 Based on this study, an extensive investigation was conducted where each component of the PWUA was assessed and modified to ensure suitability in the field. Another investigation was conducted to compare the wind uplift measurements obtained using the PWUA with the data obtained from the SIGDERS wind uplift table.5
The information obtained from the laboratory investigations was then applied to the preliminary field evaluations to assess the ability of the methodology to determine the field capacity.6 The preliminary trial allowed for the required modifications to be made to the protocols as a result of the high variability in the field. Based on the information obtained from the laboratory and field investigations, the following protocol was developed, as shown in Figure 3.
1. A minimum of three locations are selected for evaluation by the interested parties. The locations may
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Figure 3 – Portable Wind Uplift Apparatus (PWUA) for field wind uplift resistance determination and test protocol. Note for the calculation of test pressure (P): The test pressure used in the testing shall be determined according to building code requirements for a specific building, or it shall be specified by the manufacturer or client, whichever is greater.
Figure 4 – Roof assembly and test locations of school building evaluated on the East Coast for wind uplift.
include problem areas, field, corner and edge areas, or other locations based on the building requirements.
2. The PWUA is assembled on site as established by previous studies.7 Additional gaskets can be used along the perimeter of the chamber to ensure airtightness with the membrane surface.
3. The motor and valve system are used to induce a negative pressure of 15 psf, which is held for a duration of 60 seconds. The pressure is increased in increments of 15 psf for 60-second periods up until the point of failure or until a maximum target pressure determined by the interested parties. The pressure increments are depicted in Figure 3.
4. Repairs are required for areas where failure occurred and recommended for areas where component separation was evident.
The wind evaluation protocol was completed on roofs of five buildings on the East Coast of Canada and two buildings in southern Canada. The following case studies present two examples of the field results obtained and the comparison of the building code requirement with the field data and laboratory testing on roof mock-ups with similar components as that of the field testing.
CASE STUDY 1: EXISTING ROOF
On the East Coast of Canada, a school building roof was evaluated for its wind uplift resistance. The height of the building was approximately 25 ft., and the assembly composition, as well as the test locations selected, are given in Figure 4. The roof was evaluated at two different times, in
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Figure 5 – Wind uplift data at two locations on East Coast school building.
Figure 6 – Laboratory testing of 8’ x 10’ mock-up with components similar to the field testing on both the SIGDERS table and using the PWUA. System details are given in Figure 4.
December 2017 and July 2018. The roof was about four years old and was, therefore, evaluated as an existing roof. Figure 5 gives the results of evaluation of two roof locations as an example. The suction pressure that the roof assembly was subjected to is presented as a function of time. Test location 3 was able to sustain a pressure of 135 psf, after which the test was stopped. Test location 4 was able to sustain a pressure of 120 psf, and failed at the next pressure level of 135 psf, as seen in Figure 5. Locations 1 and 2 were both evaluated up to a sustained resistance of 82 psf, after which the test was stopped.
To provide a point of comparison, a test mock-up of the school building roof assembly was constructed at the NRC and evaluated using both the PWUA and the SIGDERS wind uplift tables. Both mock-ups were evaluated up to their failure pressures. The mock-up was able to resist 68 psf on the SIGDERS wind uplift table. The mock-up failed at its insulation and cover board interface, as shown in Figure 6. The PWUA evaluated on the laboratory mock-up was able to sustain a resistance of 71 psf, after which it failed within the cover board.
The laboratory results were compared with the field results, shown in Table 1, and it was observed that the sustained resistances were similar for both SIGDERS and PWUA evaluations. Three of the field trials were stopped after they reached a resistance level of either 41 psf or 68 psf; therefore, their failure pressure is unknown. However, they were able to maintain the pressures evaluated without failing. One of the field trials was taken to failure, when the corresponding sustained and failed resistances were respectively 60 and 68 psf. This observation is comparable to the laboratory data. The differences in the values can be attributed to many factors, including the age of the field assembly in comparison to the laboratory assembly, the high variability that exists in the field compared to the controlled laboratory preparation of the specimens, and the age of the field roof in comparison to the laboratory mock-up. The resulting wind uplift pressures were then compared to the National Building Code of Canada (NBCC)8 requirements. The NBCC wind uplift requirement was determined to be 32 psf. Therefore, the evaluations concluded that the roof assembly was able to exceed the NBCC requirements when evaluated with the PWUA.
CASE STUDY 2: NEW ROOF
In Ottawa, in southern Canada, a public building roof was evaluated for its wind uplift resistance. It is a high-rise building (H>60 ft.), and the assembly composition, as well as the test locations selected, are given in Figure 7. The roof was evaluated immediately after it was installed as a commissioning assessment for the building owner. Figure 8 gives the suction pressures that the roof assembly was subjected to as a function of time for the three locations evaluated. Locations 1 and 3 were both able to sustain a pressure of 150 psf, after which the test was stopped. Location 2, which appeared to have some damage, was only able to sustain a pressure of 105 psf. When the pressure was increased to the next level (120 psf), the test area failed.
The field results were compared to the laboratory evaluations and the building code requirements, shown in Table 2. The laboratory evaluation was completed by an external party, and the results were provided by the owner, which confirmed that the roof assembly was able to sustain resistance of 75 psf in the laboratory. The NBCC pressure requirement for this building in the Ottawa area was also 75 psf. Therefore, two out of three locations met the NBCC requirements when evaluated with the PWUA in the field.
THERMAL INVESTIGATION
Several existing thermal-resistance measuring methods have been reviewed.6 The most suitable method for field applications is the use of thermocouples and a heat
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Table 1 – Comparison of the design vs. evaluated vs. code-required wind uplift pressures (East Coast school).
Wind Uplift (psf)
Location Code Lab Field
Requirement (Sustained/Failed) (Sustained/Failed)
1 41/TS
2 32 SIGDERS 68/75 41/TS
3 PWUA 71/75 68/TS
4 60/68
TS= Test Stopped
Figure 7 – Roof assembly and test locations of Ottawa public building evaluated for wind uplift resistance.
flow sensor. Studies have been performed by others to measure the thermal resistance of existing buildings.9,10 Standards are also available that provide some guidance on the evaluation of the field thermal resistance.11,12 To effectively determine the field thermal resistance in a shorter time, a sufficiently high temperature difference is required across the roof assembly to simulate the driving force for the heat transfer mechanism. A methodology was applied whereby a desired steady-state temperature differential was induced across the roof assembly. A thermally shielded chamber (TSC) was placed above the roof assembly (Figure 9). The chamber contained a heat source that was adjusted to a desired temperature setpoint to achieve the target temperature differential across the assembly. To measure the temperatures, thermocouples were installed—both on the exterior membrane top surface and on the interior deck bottom. A heat flux sensor was placed on the surface of the membrane within the TSC to measure the heat transfer across the roof assembly. The following tentative protocol is being developed, as shown in Figure 9.
1. Locations are selected for thermal investigation based on the building requirements and agreement by the interested parties.
2. The heat flux sensor and a thermocouple are installed on the membrane top surface at desired locations. The instruments are attached to the surface using contact tape or conductive gel. A second set of thermocouples is attached below the deck using contact tape. The instruments are connected to data acquisition (DAQ) devices.
3. The TSC is placed above the thermocouple and heat flux sensor and sealed along its perimeter to control heat loss and air/water entry.
4. The heat source within the thermal chamber is set to its target value. It is optimal to have a minimum temperature differential of 72ºF (40ºC) to provide a required driving force.
5. The system is subjected to an initial period of fluctuation—typically between eight and 12 hours—where the temperature within the TSC is increasing to meet its target value. The duration of the period of fluctuation is dependent on various factors, including the presence of moisture, contacts with the membrane, and roof assembly components. The TSC is considered to be within the stabilization region once there is less than 10% change in the temperature differential and the thermal resistance. The thermal resistance is determined from the relation: R = ΔT/Q, where ΔT is the temperature difference across the assembly measure from the installed thermocouples and Q is the heat flux measured by the heat flux transducer installed on the membrane surface.
The thermal resistance evaluation protocol was completed on four buildings on the East Coast of Canada and two buildings in southern Canada. The following case studies present two examples of the field results obtained and the comparison of the data with laboratory evaluations of test cuts, calculated predictions based on manufacturer-provided estimates, and energy code requirements.
CASE STUDY 3: REROOFED ASSEMBLIES
In Ottawa, in Southern Canada, a commercial building was evaluated for its thermal resistance. The assembly composition is given in Figure 10 and consisted of three layers of polyisocyanurate (polyiso) insulation with total thickness of 7.5 in. The commercial building had been reroofed in various sections, and this particular area was reroofed in 2017. The TSC was installed on the roof sections, as shown in Figure 10, and the test protocol was implemented to measure the field thermal performance. Three test locations were investigated following this procedure.
Figure 11 gives an example of the measurements obtained in the field for Site 1. The measured field thermal resistance (R-value) was determined to be 33.5ºFft2hr/Btu. A cut was made on the field roof to extract a test specimen of the roof assembly. The insulation component of the test specimen collected was evaluated in the laboratory following the ASTM C518 test protocol maintaining similar temperatures to the field evaluation (i.e., ΔT= 68ºF and
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Table 2 – Comparison of the design vs. evaluated vs. code-required wind uplift pressures (Ottawa public building).
Wind Uplift (psf)
Location Code Lab Field
Requirement (Sustained/Failed) (Sustained/Failed)
1 75/TS
2 75 75 53/60
3 75/TS
TS= Test Stopped
Figure 8 – Wind uplift field pressure data for various locations on the Ottawa public building.
Tmean=106ºF).13 Through the laboratory evaluation, the thermal resistance of the insulation was determined to be 39.9ºFft2hr/Btu. The theoretical thermal resistance of the insulation was calculated using the nominal thermal values provided by the manufacturers. Based on the insulation composition, the calculated thermal resistance was 42.8ºFft2hr/Btu. It should be noted that the manufacturer-provided nominal thermal resistance values are obtained at Tmean of 75ºF. The values obtained were compared with the minimum effective R-value requirements of the National Energy Code of Canada for Buildings (NECB),14 which is 31.0ºFft2hr/Btu for the Ottawa location. Note that the NECB effective R-Value requirement of 31.0ºFft2hr/Btu is referenced to a mean temperature of 75ºF. Although this direct comparison with the building code is not appropriate due to involved variables such as the performance of TSC, temperature dependency performance of insulation, and long-term thermal resistance of the insulation, the intent of this comparison is to highlight the performance of the current assembly relative to the minimum code requirements.
It appears that Site 1, which had recently undergone reroofing, has sufficient thermal insulation to meet the NECB requirements. However, since it is a mechanically fastened insulation, the impact of thermal bridging on the effective
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Figure 10 – Reroofed assembly evaluated for thermal resistance and installation of TSC and instrumentation.
Figure 9 – Thermal resistance apparatus for field thermal resistance determination and NRC target experimental protocol.
R-value needs to be evaluated and verified with the code requirements.
Two other sections of the commercial roof were also investigated, with varying insulation compositions, detailed in Table 3. Site 2 had been reroofed in 2016, and Site 3, in 2013. These sections were also evaluated for their field thermal resistance using the NRC protocol. The measured field thermal resistance was determined to be 10.5ºFft2hr/Btu and 13.8ºFft2hr/Btu, for Site 2 and Site 3, respectively. Through the laboratory evaluation on the field test specimens, the thermal resistances of the insulations were determined to be 16.3ºFft2hr/Btu and 16.1ºFft2hr/Btu, for Site 2 and Site 3, respectively. Based on the insulation composition, the calculated thermal resistances were 19.0ºFft2hr/Btu and 17.8ºFft2hr/Btu for Site 2 and Site 3, respectively. Sites 2 and 3 did not meet the current NECB requirements.
As shown in Table 3, similar mean temperature conditions are used for the lab and field measurements, which were higher than the NECB reference mean temperature. Irrespective of that, based on the manufacturer-provided nominal thermal resistances, it is evident that Sites 2 and 3 do not have sufficient insulation to meet the current energy code requirements. To improve the thermal performance and meet the current NECB requirements, retrofitting them with additional insulation thickness would be required.
CASE STUDY 4: EXISTING ROOF UPGRADE REQUIREMENTS
Another roof—a building at NRC in Ottawa—was assessed for its remaining field thermal resistance capacity (Site 4). The assembly composition is given in Figure 12 and consisted of 3.13 in. of mineral wool insulation. The TSC was installed on the roof, and the thermal performance was assessed using the developed NRC protocol. Figure 12 gives the temperature differential and the thermal resistance that were obtained from the field measurements. With a temperature differential of approximately 75ºF and Tmean = 89ºF, the measured field thermal resistance was 11.3ºFft2hr/Btu.
The roof was then cut to remove a specimen for evaluation in the laboratory heat flow meter. The test specimen comprised only the mineral wool insulation. The laboratory evaluation as per the ASTM C518 protocol at the similar field temperature conditions gave a thermal performance of 10.9ºFft2hr/Btu. Based on the nominal thermal resistance value at Tmean = 75ºF, the calculated thermal resistance was determined to be 12.5ºFft2hr/Btu. The field and laboratory-measured thermal resistances were within 10% agreement. The NEBC requirement for the Ottawa commercial building is 31.0ºFft2hr/Btu. Again, the NECB effective R-Value requirement of 31.0ºFft2hr/Btu is referenced to a mean temperature of 75ºF. Therefore, in order for the NRC roof to meet the current energy code requirements, the thermal resistance must be increased by approximately 20ºFft2hr/Btu.
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Figure 11 – Sample field thermal resistance measurements on Ottawa commercial building (Site 2).
Table 3 – Validation of the thermal resistance obtained in the field with a laboratory evaluation, calculated, and code requirement for Ottawa commercial building.
Site Details Parameters Field Laboratory Calculatedi NECB 2015, Ottawa
Site 1 – 2017
7.5” Polyiso ΔT, °F 68 68 – –
Tmean, °F 104 106 75 75
R,
°Fft2hr/Btu 33.5 39.9 42.8 31.0
Site 2 – 2016
1” Mineral Wool ΔT, °F 87 83 – –
1.5” Polyiso Tmean, °F 114 112 75 75
2” Fiberglass R, °Fft2hr/Btu 10.5 16.3 19.0 31.0
Site 3 – 2013
2” Polyiso ΔT, °F 51 52 – –
2” Fiberglass Tmean, °F 97 98 75 75
R,
°Fft2hr/Btu 13.8 16.1 17.8 31.0
iBased on nominal R-value provided by manufacturer
Figure 13 provides a summary of the thermal investigations for all sites with the respective roofed year. The field measurements were compared to the laboratory evaluations conducted on a test cut specimen, as well as calculated based on nominal component thermal properties. It should be noted that field measurements refer to assembly performance, while the laboratory and calculated values refer to material performance; also, the reported values from field and laboratory are at different mean temperatures compared to the calculated values.
Of the sites evaluated, only Site 1 met the current code requirement of 31.0ºFft2hr/Btu. This requirement was met by all three approaches: field, laboratory, and calculation. The other three sites require insulation retrofit in order to meet the current code requirement.
WATERTIGHTNESS INVESTIGATION
An important element of climate resiliency in commercial roofs is watertightness. There are many tools and techniques that currently exist to evaluate the watertightness of a roof assembly, which have been published in previous studies15 and summarized in Annex A. It was determined that although there are many techniques that exist in the industry, there is no single straightforward method to accurately evaluate the water ingress from the exterior to the interior. This leads to confusion as to which method is most appropriate for which type of roof, and what information the test provides.
Based on the completed review, presentations were made to the RICOWI moisture committee. Together with member input, it was determined that there is no single method that exists to detect the exterior water entry into roof assemblies. A common industry practice is to perform a combination of applicable methods to both detect the presence of water in a roof assembly and identify the source of the leak. Since infrared thermography is the most simple and convenient method, it is often used in conjunction with another more technical method to detect the presence of water.
The watertightness evaluation should not only be conducted for commissioning or in the aftermath of a major weather event. Watertightness evaluations should be included in regular maintenance as a tool to monitor the water resistance. Without performing regular watertightness evaluations, the building owner will either
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Figure 13 – Comparison of field thermal resistance measurements with laboratory, calculated, and energy code requirements.
Figure 12 – Roof configuration details and field thermal resistance measurements on NRC building (Site 4).
be left guessing if there is a problem with his or her roof or will only be made aware of an issue once it has progressed to visible interior damage. By combining water detection methods that are suitable for a particular system, one can obtain information regarding the watertightness resistance of a roof assembly.
CONCLUDING REMARKS
Roofs were evaluated in both eastern and southern Canada to determine their field wind uplift and thermal resistances. The investigation included existing and new roofs, which were assessed for their remaining capacity, and installed commissioning capacity, respectively.
• For the two wind case studies presented, it was determined that the field wind uplift resistances were consistent with the laboratory investigations and mostly met the code requirements.
• For the thermal case studies presented, the 2017 reroofed site had sufficient thermal resistance to meet the requirements of the code. However, the other sites investigated required the installation of additional insulation to meet the current thermal resistance requirements.
• A watertightness investigation review was also published, which describes the methodologies that can be applied to determine the field watertightness of a roof assembly.
The protocols developed for wind, thermal, and watertightness provide the industry with a useful tool to commission and assess building performance through field evaluation. Through implementation of the field installation and commissioning element, in addition to code requirements and designs, durable roofs can be achieved to ensure climate resiliency.
ACKNOWLEDGEMENTS
The authors would like to thank: SIGDERS membership; Lee Everett of the government of New Brunswick; Gary Hamilton of the New Brunswick Roofing Contractors Association; Jean-Guy Levaque, Stephanie Robinson, and Cameron Wynn of WSP Canada Inc.; and Ted Sheridan and Jake Brown of Fishburn Sheridan & Associates Ltd., for their contributions to the NRCC’s climate resilience project.
REFERENCES
1. A. Baskaran, S. Molleti, D. Lefebvre, and D. van Reenen. “Climate Change Adaptation Technologies for Roofing and Insulation.” National Research Council of Canada. Ottawa, 2017.
2. A. Baskaran, S. Molleti, D. Lefebvre, and N. Holcroft. “Climate Change Adaptation Technologies for Roofing.” In Proceedings of the 33rd RCI International Convention and Trade Show. Houston, TX, 2018.
3. M. Bartko, S. Molleti, and A. Baskaran. “In situ Measurements of Wind Pressures on Low-slope Membrane Roofs.” Journal of Wind Engineering and Industrial Aerodynamics. Vol. 153, pp. 78-91. 2016.
4. R. P. Canon, B. S. Joplin, and S. T. Watson. “SMARF Building Cape Canaveral Air Force Station, Florida.” RCI Interface. Vol. 20, no. 9, pp. 24-36. 2002.
5. S. Ko, D. Lefebvre, M. Chavez, and A. Baskaran. “Comparison of Wind Uplift Data Obtained from a Portable Wind Uplift Apparatus vs. SIGDERS.” National Research Council of Canada, Ottawa, 2018.
6. A. Baskaran, D. Lefebvre, S. Ko, and M. Chavez. “Guidelines for Commissioning and Certifying the Resiliency of Roofs Subjected to Extreme Weather Events: Year 1 Progress Report.” National Research Council of Canada, Ottawa, 2018.
7. S. Ko, D. Lefebvre and A. Baskaran, “Suitability of a Portable Wind Uplift Apparatus for Field Trials.” National Research Council of Canada, Ottawa, 2018.
8. Canadian Commission on Building and Fire Codes. “National Building Code of Canada.” National Research Council of Canada, Ottawa, 2015.
9. M. Scarpa, P. Ruggeri, F. Peron, M. Celebrin, and M. De Bei. “New Measurement Procedure for U-value Assessment via Heat Flow Meter.” Energy Procedia. Vol. 113, pp. 174-181, 2017.
10. A. Rasooli, L. Itard, and C. I. Ferreira. “A Response Factor-based Method for the Rapid in-situ Determination of Wall’s Thermal Resistance in Existing Buildings.” Energy and Buildings. Vol. 119, pp. 51-61, 2016.
11. ASTM International. ASTM C1046, Standard Practice for In-Situ Measurement of Heat Flux and Temperature on Building Envelope Components.” West Conshohocken, PA. 2013.
12. International Organization for Standardization. “ISO 9869-1, Thermal Insulation – Building Elements – In-situ Measurement of Thermal Resistance and Thermal Transmittance – Part 1: Heat Flow Meter Method.” 2014.
13. ASTM International. ASTM C518, Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus.” West Conshohocken, PA, 2015.
14. Canadian Commission on Building and Fire Codes. “National Energy Code of Canada for Buildings.” National Research Council of Canada, Ottawa, 2015.
15. D. Lefebvre and A. Baskaran. “Identifying Watertightness of Low-slope Roof Membranes.” Construction Canada, 2019.
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Deploy electric conductance methods to verify the integrity of membranes that are not electrically conductive.
A conductor cable loop is installed around the perimeter of the area to be tested. The cable loop is connected to a low-voltage pulsating generator, and the upper electrical plate is formed by dampening the area within the loop. By grounding the conductive deck, it acts as the lower electrical plate, and the roof membrane acts as the insulator.
When a breach is present, current will flow through the opening of the membrane to the deck, completing the circuit.
Yes
No
No
Wet insulation with higher thermal mass retains heat longer than dry insulation.
Infrared imaging is used to determine the location of wet insulation (in contact with the membrane) in the roofing system.
At night, when the roof begins to cool, the wet insulation (higher mass) retains heat longer than the dry area (lower mass). The infrared camera is able to capture the temperature differential between the dry and wet areas.
No
Yes
Yes, with core samples
One electrical lead is connected to the roof deck, while another is attached to the device (which resembles a push broom with copper bristles). The membrane acts as an insulator.
When a breach is present in the membrane, the electricity will flow through the defect and ground to the conductive roof deck.
Drains provide good grounding components, as the drain lines are secured to the structure. Drains with PVC piping are ineffective. Metal vent pipes, metal flashings, and exposed rebar secured to the structure are additional grounds.
Yes
No
No
Radioisotopic thermalization – a process where high-velocity neutrons lose energy due to collision with hydrogen atoms.
The nuclear moisture meter emits high-velocity neutrons and measures backscattered slow neutrons, which have lost much of their energy in collisions with hydrogen atoms. Thus, higher levels of slowed neutrons are recorded at wet areas (water contains a significant amount of hydrogen atoms).
No
Yes
Yes, with core samples of dry and wet locations
Wet insulation provides less resistance to electrical current than dry insulation.
The electronic impedance (EI) of materials in the roofing system directly under the scanner is measured by creating an alternating electric field that penetrates the materials. The small alternating current flowing through this field is inversely proportional to the impedance of the moisture-absorbing materials.
No
Yes
Yes, with core samples of dry and wet locations
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ANNEX A – SUMMARY OF WATERTIGHTNESS EVALUATION (A VERSION OF THIS WILL BE PUBLISHED IN “IDENTIFYING WATERTIGHTNESS OF LOW-SLOPE ROOF MEMBRANES, CONSTRUCTION CANADA.”)15
Low Voltage –
Wet Method
ASTM D7877
Infrared Thermography
ASTM C1153
TAS 126-95
Electrical Impedance
ASTM D7954
TAS 126-95
High Voltage –
Dry Method
ASTM D7877
Nuclear
TAS 126-95
ANSI/SPRI RCI NT-1-2017
Scientific Basis
Method of Operation
Ability to identify the leak source
Ability to detect
moisture accumulation
in insulation
Ability to measure the moisture content
• Applicable to protected membrane roof assemblies (PMR) /inverted roof membrane assemblies (IRMA)
• Applicable to overburden roof assemblies; i.e., vegetated roof assemblies
• Not applicable to black EPDM and butyl membranes or membranes with aluminized protective coating due to high electrical conductivity
Not applicable to systems with cover boards. Cover boards block the electrical field unless a conductive material (wire grid or conductive primer) is placed directly under the membrane
Not applicable to systems with insulation. Insulation will block the electrical field
Not applicable to systems with vapor retarders. Vapor retarders mask the breach by blocking the electrical field.
• Applicable to conventional roof assemblies
• Not suitable for ballasted roof assemblies and PMR
• Applicable to all types of membranes
• Membrane must be dry
Yes
Not suitable for insulations that do not absorb water (EPS or closed-cell spray polyurethane foam)
• Applicable to conventional roof assemblies
• Applicable to overburden roof assemblies; i.e., vegetated roof assemblies
• Not applicable to black EPDM membranes or membranes with aluminized protective coating due to high electrical conductivity
• Membrane must be completely exposed and must be dry
No information
No information
• Applicable to conventional roof assemblies
• Applicable to ballasted roof assemblies and PMR, only if ballasts or pavers are removed from the test area
• Applicable to all types of membranes
Yes
Yes
• Applicable to conventional roof assemblies
• Applicable to ballasted roof assemblies and protected membrane roof assemblies, only if ballasts or pavers are removed from the test area
• Not applicable to black EPDM membranes or membranes with aluminized protective coating
• Membrane must be dry
Yes
Yes
RCI International Convention and Trade Show • MarcRCh 14-19, 2019 B BaSKaran and Lefebvre • 75
Low Voltage –
Wet Method
ASTM D7877
Infrared Thermography
ASTM C1153
TAS 126-95
Electrical Impedance
ASTM D7954
TAS 126-95
High Voltage –
Dry Method
ASTM D7877
Nuclear
TAS 126-95
ANSI/SPRI RCI NT-1-2017
Roof assembly
Membrane
Cover board
Insulation
Vapor barrier
76 • BaskSKaran and Lefebvre RCI International Convention and Trade Show • MarcRCh 14-19, 2019
Conductive deck; i.e., steel deck, concrete deck
• Potential for false positive
• Operator’s experience is important for interpreting results accurately.
Not suitable for roof decks capable of retaining significant quantities of construction water (wet-applied deck such as lightweight concrete decks and poured gypsum decks)
• Potential for false positive
• Operator’s experience is important for interpreting results accurately.
• Testing must be done at night.
• Can provide misleading information of warm areas due to mechanical equipment, under-deck heating or cooling unit, or shaded areas.
• Potential for false positive
• Operator’s experience is important for interpreting results accurately.
• If water is present behind flashings or under the membrane from adjacent surfaces (e.g., windows, storefronts, porous masonry, or unsealed base flashings), no reading will be obtained as no membrane breach will be detected.
• More false-positive results have been reported using this method compared to the low-voltage method.
Not applicable to metal roof systems
• Potential for false positive
• Operator’s experience is important for interpreting results accurately.
• Meter readings are angle-sensitive and must be properly placed on the roof.
• The nuclear meter samples about 2 ft2 at each grid point (3’ x 3’, 6’ x 6’ or 10’ x 10’ grid pattern).
• Operator licensing is required by the United States Nuclear Regulatory Commission (USNRC).
• A baseline reading (calibration for the meter) needs to be taken in a known dry area of the roof.
• Ponded water will result in increased readings.
• The readings can be affected by inconsistencies in the roof components.
• The equipment has a depth limitation of 6-8’’ for detecting moisture.
• Potential for false positive
• Operator’s experience is important for interpreting results accurately.
• Aggregate-ballasted and aggregate-surfaced membranes with variable aggregate size and weight may reduce instrument sensitivity.
• Scanners are more sensitive to interply moisture and moisture closer to the scanner electrodes.
• Roof patches that are dissimilar to the roof system under test may give erroneous readings.
• The presence of dew, rain, snow, and ice significantly affects the impedance readings.
Low Voltage –
Wet Method
ASTM D7877
Infrared Thermography
ASTM C1153
TAS 126-95
Electrical Impedance
ASTM D7954
TAS 126-95
High Voltage –
Dry Method
ASTM D7877
Nuclear
TAS 126-95
ANSI/SPRI RCI NT-1-2017
Decks
Cons
RCI International Convention and Trade Show • MarcRCh 14-19, 2019 B BaSKaran and Lefebvre • 77
• Works on membranes with ballast or lightweight soils.
• Allows the operator to sample the entire roof.
• Not time consuming.
• Not dependent on the climatic conditions.
• Easy to use.
• Less sophisticated.
Low Voltage –
Wet Method
ASTM D7877
Infrared Thermography
ASTM C1153
TAS 126-95
Electrical Impedance
ASTM D7954
TAS 126-95
High Voltage –
Dry Method
ASTM D7877
Nuclear
TAS 126-95
ANSI/SPRI RCI NT-1-2017
Pros