Roof Assemblies Research Articles

Influence of glazing size on energy efficiency of timber-frame buildings

Competitive fields of residential building are aware that today’s prefabricated timber building is extremely highly valuated and is capable of fulfilling all of the demands from our society and from the environment that we live in. Additionally, due to strict energy requirements, the tendency to use a higher share of glass wall surfaces occurs worldwide. Therefore, the aim of this research is to investigate an alternative solution by using a glass sheathing material instead of classical wood-based or fibre-plaster sheathing boards in timber-framed walls as the main load-bearing elements in prefabricated timber-framed buildings with a special focus on the annual energy demand behaviour for heating and cooling. The research is based on a case study of a two-storey house with a prefabricated timber-frame structural system and its parametric analysis of an increased-proportion-of-the-glazing-surfaces impact, taking the climate data for Ljubljana into consideration. The analysis was carried out on different exterior timber-frame wall elements having different thermal properties, while the rest of the parameters, such as the ground plan of the model as well as the active systems, roof and floor slab assemblies remain constant. The graphical presentation includes a function curve showing the annual energy demand for heating and cooling depending on the proportion of the glazing area in relation to the total surface area of the south-oriented façade. The comparative analysis results can nevertheless serve as a good frame of reference to civil engineers and architects in an approximate estimation of energy losses accompanying the different positioning and proportion of glazing surfaces while using various prefabricated timber-frame wall elements as well as serving some basic principles in the energy refurbishment of old timber-frame buildings.

Roofing Assembly Simulated Heat and Light Test

Abstract The goal of this project is to search for a testing procedure for roof covering products that will radiate both heat and light onto a roof covering and then measure the impact that a given roof covering product has on heat transfer through the entire roofing assembly. Identical roof assemblies were built with ethylene propylene diene terpolymer (EPDM) rubber roof membrane over a wood deck. Sixteen heat lamps were positioned 1.14 m [45 in.] above the roof covering product to provide both heat and light. Thermocouples were placed on the underside of the wood deck and were insulated from outside air. The roofing assembly and the roof covering temperatures were brought to 18°C to 21°C prior to testing. Heat and light were radiated onto the roof coverings for 360 min and the under deck temperature was recorded at 1 min intervals for 600 min. Tested roof coverings included gravel, growing media, coatings, and panels in the form of concrete, ceramic foam, and rubber. The results of the tests have shown data similar to that which were recorded during warm, sunny days. As expected, the highest temperatures were achieved by the uncovered and uncoated black EPDM roof assembly. The temperature of this assembly diminished almost immediately upon the removal of the heat and light source. Thicker layers of growing media and ceramic foam block did not reach the peak temperature until several hours after the heat lamps were turned off. The roof assembly covered with reflective coating showed realistic resistance to the heat and light source. This is a significant advancement in the effort to provide equitable data for all roof coverings. The test provides a standard method of collecting data for traditional roof coverings as well as emerging technology roof covering materials to evaluate a roofing assemblies’ thermal performance from solar heat gain.

Thermal Energy Performance of a Solar Thermal Electric Panel

The main goal of this research was to develop and understand the performance of a hybrid roof system that combined an amorphous junction photovoltaic panel in combination with copper panel and tubing encased in a low-iron glass. The setup encompassed 160 sq ft of the solar thermal electric panel (STEP) system supplied with a glycol-water closed-loop system. The system was fixed to a simulated roof assembly built at the optimal angle of 61° for winter solstice for the local area (Rolla, Missouri). The encased combination panel provided consistent electrical efficiency and mixed thermal efficiencies based on the hours of operation. In conclusion this paper will discuss experimental performance analysis on the STEP system thermal and overall outcomes. Further testing on the effects of a glazed versus unglazed panel yielded a 23% reduction in solar electric production; however, it increased thermal collection by approximately 200%. The present study shows that the idea of a STEP system is viable. A prototype hybrid solar thermal electric panel system was implemented in the Missouri Univ. of Science and Technology’s solar house entry into the 2005 solar decathlon, and today the solar house is part of student housing and the solar research facility at Missouri Univ. of Science and Technology.

Dual Barrier Protected Membrane Roof Assemblies

Abstract Durable roof design is accomplished through the selection of proven high performance materials that are detailed to accepted standards and assembled by skilled tradespeople. Leak prevention is a high concern of building owners that can be addressed by protected membrane dual barrier roofs. The case studies herein illustrate the improvement of the membrane and insulation. Typically, roofing membranes are generally the only barrier for managing moisture (rain, vapor pressure, air movement) through a building’s roof. The position of the insulation is also an important consideration because insulation on the membrane’s exterior protects it from thermal shock and generally extends the roof membrane’s service life. Largely for this reason, protected roof membranes have been recognized for their superior performance over that of conventional roofs because the insulation protects the primary roofing membrane from wide temperature fluctuations, solar radiation, and foot traffic over the roof membrane. The concept of dual barrier roofing simply includes (a) designing a new roof assembly to include at least one “extra” layer of moisture protection or (b) simply designing the standard existing roof components to resist the elements in order to further improve the performance of a protected roof assembly. Case studies are presented that summarize the physical attributes for dual barrier roofing, both in new construction and for roof replacement/renewal projects. Measured performance comparisons indicate that a dual barrier protected membrane roof can be on the order of 10 % to 20 % more thermally efficient that a typical protected membrane [Tobiasson, W., and Richard, J., “Moisture Gain and Its Thermal Consequence for Common Roof Insulations,” NRCA Fifth Conference on Roofing Technology, US Army Cold Regions Research & Engineering Laboratory, Gaithersburg, Maryland, April 1979; Beech, J. C., and Saunders, G. K., “The Performance of Lightweight Inverted Flat Roofs, Building Research Establishment,” NRCA Second International Symposium on Roofing Technology, Princes Risborough Laboratory, Buckingshamshire, United Kingdom, September 1985]. Additional performance and service life benefits are also summarized.

Case Studies of Foamed Adhesive Failures of Low Sloped Roofing Rigid Insulation Board

Abstract In low sloped roofing systems, poorly adhered roofing assemblies are unable to resist significant wind loads and are likely to be further damaged or destroyed by wind events well below the design wind pressures for the assembly. The design and installation of rigid insulation boards are a critical parameter in the service life of this roofing assembly in that, if the insulation boards become detached, there is increased risk for complete roofing assembly failure. Foamed adhesive is a common alternative to traditional hot-mopped asphalt adhesive in contemporary roofing assemblies. The proper design and installation of insulation board roofing assemblies in foamed adhesive is paramount to the successful performance of these roofing assemblies. Some of the critical parameters that could influence foamed adhesive performance are: insulation board adhesive pattern defects; insulation board adhesive quantity; inadequate insulation board adhesive contact; and failure to maintain insulation board contact with the substrate until the insulation adhesive is sufficiently set. The present paper discusses these critical parameters through case studies that clearly demonstrate how these parameters can lead to the failure of roofing assemblies, and discusses the lessons to be learned from these insulation board adhesion failures.

Wind Uplift Performance of Composite Metal Roof Assemblies

A common factor in roof failures is wind forces, which inflict considerable damage every year, even to new roof structures. Metal roofs are a popular low-sloped roof assembly. On the basis of their layout, metal roofs can be categorized as either composite or noncomposite assemblies. In North American practice, five main test procedures—ASTM E1592, ANSI/FM 4474, UL 580, UL 1817, and CSA A123.21-04—are used to determine the wind uplift performance of metal roofs. The fundamental differences between these test protocols lie in the way they represent wind effects on the performance of metal roofing systems. Of the five, CSA A 123.21-04 is the only one that assesses the wind uplift resistance under dynamic wind load conditions. To evaluate the wind uplift performance of noncomposite and composite metal roofing assemblies, eight assemblies with two different types of panels—SNAP-IT and MR-24—were tested by using the CSA A123.21-04 dynamic test protocol. By relating air intrusion characteristics of the subsurface components to panel behavior, this paper shows how composite assemblies resist wind uplift pressures better than noncomposite assemblies. This paper reveals that increased air intrusion resistance of the sub surface components in composite assemblies results in increased suction resistance, decreased panel deflection, decreased stress on the panels, and increased wind uplift resistance.

A Test Protocol to Quantify the Uplift Resistance of Adhesive Applied Roofing Specimens Subjected to Tensile Loading

Abstract Adhesive applied roofing systems (AARS), a new generation of built-up roofs, are gaining popularity in North American low slope application. AARS uses no fasteners and all components (e.g., deck, vapour barrier, insulation board, and membrane) are integrated by the use of adhesives. As there are no metal fasteners, AARS can offer an advantage of reduction in condensation and thermal bridges for the roof assemblies. Even though, AARS have been in use, there have been no standard that exists to quantify its wind uplift performances. An industries-university-Canadian government collaborative research project, “Development of Wind Uplift Standard for Adhesive Applied Low Slope Roofing System,” has been initiated with three major tasks: Experimental investigation, formulation of a numerical model and development of wind design guide and standards. This paper documents a standardized small scale laboratory test method for the quantification of uplift resistance subject to tensile loading. As part of Task 1 of the project, this systematic investigation focuses on three key parameters: Loading rate, specimen size and end condition. The investigations were completed by constructing over 400 specimens. Both the maximum uplift resistance and the consistence in the failure plane are equally considered during the test method standardization. The data from this small scale testing can facilitate roofing industries to optimize the material combinations such that the uplift resistance data can be used as an indicator before performing a full-scale wind uplift testing.

An investigation of sensible heat fluxes at a green roof in a laboratory setup

During the last few years, several models have been proposed for the calculation of green roof thermal behavior, but the validation studies of such models are lacking a comprehensive set of highly accurate data. In this study, an experimental laboratory setup was used to create different environmental conditions and to measure sensible heat fluxes to/from a vegetated roof assembly. This experimental setup has been successfully used for different wind velocities (0–3 m/s) to create free and forced convection conditions around green roof tested samples. Furthermore, our study proposed a “basic model” for calculations of the convective heat transfer at green roof assemblies, which is a modified version of the Newton’s cooling law, calibrated and then validated with different sets of data. For forced convection flow regimes, the proposed “basic model” resulted in RMSE (Root Mean Square Error) of 11 W/m 2 and R 2 value of 0.81. Similarly, the model provided RMSE of 6.6 W/m 2 and R 2 of 0.90 for sensible heat fluxes with free convection conditions. In the future, this model will be used in on-site experimental studies to understand its performance under wind conditions that exhibit a much wider range than the studied velocity range near the leaf canopy.

A Test Protocol to Quantify the Peel Resistance of Adhesive Applied Low Slope Roofing Specimens Subjected to Shear Loading

Abstract Adhesive Applied Roofing System (AARS)s are regaining popularity in the Canadian low slope application. AARSs use no fasteners. All components (e.g., steel deck, vapour barrier (if any), insulation board, cover board, base sheet, and cap sheet) are integrated using cold adhesives and presented as a new generation of Built-Up Roofs. As there are no metal fasteners, AARSs can offer an advantage of a reduction in the moisture migration and thermal bridges of the roof assemblies. Moisture in the roof envelope can lead generally to material deterioration, structural integrity problems, and the growth of mould. Even though AARSs have been in use, existing uplift standards do not certify them for wind uplift performances. A new project, the “Development of Wind Uplift Standard for Adhesive Applied Low Slope Roofing System,” has been initiated in collaboration with industries, universities, and government departments. The project has three major tasks: Experimental investigation, formulation of a numerical model, and development of wind design guide and standards. This paper documents a segment of the findings from this project. Under Task 1, investigations were completed by constructing over 600 specimens constructed using cold adhesives and examining the peel resistance of bonded roofing components through mechanical separation of bonded layers by applying shear forces. These specimens use the insulation and the cover board components exclusively because they are more vulnerable to peeling under shear forces. Based on this scrutiny, three key parameters; namely, peel position, peel angle, and specimen size were optimized. This paper presents the findings and development of a standardized test method to determine the peel resistance of AARS specimens.

Quantification of Uplift Resistance of Adhesive-Applied Low-Slope Roof Configurations Subjected to Tensile Loading Test Protocol

The Adhesive-Applied Roofing System (AARS) is a new generation of built-up roofs gaining popularity in North American low-slope application. AARS uses no fasteners, and all components (e.g., steel deck, vapor barrier, insulation board, cover board, and membrane) are integrated by application of adhesives. Although AARS has been in use, existing standards address only mechanically attached or bonded roof assemblies. To quantify the wind-uplift performance of the AARS, an industry–university–government collaborative research project, Development of Wind Uplift Standard for Adhesive-Applied Low-Slope Roofing System, has been initiated. The project has three major tasks: experimental investigation, formulation of a numerical model, and development of wind design guide and standards. Task 1 developed test protocols to quantify the uplift and peel resistance of small-scale AARS specimens respectively subjected to tensile and shear loading. Using the standardized tensile test parameters, this paper identifies th...

Air intrusion and its impact on energy performance of roofing assemblies

Air intrusion through roof assembly is a concern for wind uplift resistance and life-cycle performance of roofs. Airflow control is usually achieved by the installation of an air barrier/retarder in the roofing assembly. Even though the concept of air barrier/retarder and air barrier systems has been around for decades, it is still considered a new notion to the roofing industry. Currently, there are no widely accepted standard specifications or test methods to determine air intrusion through roofs or roof assemblies. An experimental procedure has been under development at the National Research Council of Canada to quantify the air intrusion of roof assemblies. As part of this investigation, five roofing assembly configurations were quantified for air intrusion. Relative performance of the air retarding effect of the five assemblies indicated that assemblies with air barrier/retarder had lower air intrusion rates than without. Measured air intrusion rates are compared with the existing codes of practice and standards. This comparison clearly demonstrates the significance of air intrusion into the roofing assembly and the necessity of a standardized air intrusion test method for the roofing industry. With the measured data, attempts were made to perform thermal load calculations using a simplified procedure, and through two case studies the impact of air intrusion through roofing assemblies on energy performance was estimated.

CFD modelling and thermal performance analysis of a wooden ventilated roof structure

Thermal comfort and energy saving are objectives of key significance that building design must meet. Since a low energy building can be obtained as a result of the good realization of all its components, roofs call for particular attention as they represent a large part of a building’s total surface area. In this paper the benefit of using ventilated roofs for reducing summer cooling load is investigated. The investigation has been conducted comparing a ventilated roof assembly with different channel heights (3 cm, 5 cm, and 10 cm) to the same non ventilated structure, assuming buoyancy-driven airflow. Direct comparison between the open and the closed roof structures as a function of different cavity heights and outside environmental conditions is presented. To provide fundamental information about the thermal performance of these building envelope components, the computational fluid dynamics (CFD) model has been used to develop correlations for the characterization of the airflow and heat transfer phenomena in the ventilation cavity which have been implemented in a whole year energy simulation software. The present analysis shows a conflicting discrepancy among the indexes of performance describing the actual energy saving potential of a ventilated roof.

Effect of Fastener-Deck Strength on the Wind-Uplift Performance of Mechanically Attached Roofing Assemblies

A roofing system consists of a waterproof membrane, attachments, cover board (if present), insulation, and vapor or air barrier [retarder (if present)]. A roof assembly is a roof system that includ...

Compact Asphalt Shingle Roof Systems: Should They be Vented?

Abstract Traditional steep-slope roof systems for the residential buildings (single-family homes and multi-building apartment or condominium buildings) consist of asphalt glass-fiber shingles applied over vented or unvented attics. The long-term performance of these roofs is primarily dependent on geographic location, proper roof ventilation, roof slope, material component selection and color, as well as proper detailing and construction. There is a trend towards maximizing interior space in residential dwellings by constructing compact steep-slope roof systems with cathedral or vaulted ceilings without proper venting of the asphalt shingle roof system, which, in turn, may reduce the life of the shingles. The primary reason for venting is to convey water vapor. Build up in the roof, to outside the building. Although few building code jurisdictions are relaxing the requirement for roof ventilation in compact steep slope roof systems, ventilation is still typically required by most building codes. Where allowed by the code, designers and contractors tend to omit the vented air space and favor the use of closed cell spray-applied foam insulations (polyurethane) or permeable insulation combined with vapor retarders to help control the build up of destructive moisture levels within the roof. This article presents the results of numerical case studies created in WUFI® that demonstrate the need for venting in unvented asphalt shingle roof systems with a variety of insulation and vapor retarder materials in a hot (Miami, FL) and cold (Boston, MA) climates. The models utilize historical hourly weather data to simulate the time-varying exterior conditions and examine the effect of natural ventilation and incidental roof leakage on hygrothermal performance of unvented and vented steep-slope roof assemblies. The interior conditions for residential buildings in the models are set at 21.1°C±1.1°C (70°F±2°F) and 35 %±15 % relative humidity. We selected the drying potential and the robustness of the moisture-sensitive roof system materials in response to incidental roof leakage to measure the performance of the roof assembly. Our study showed better durability of vented roof assemblies with permeable insulation in cold climates due to redundancies that can tolerate incidental moisture and provide visual indicators of roof leakage; roof sheathing typically dries in 1-1/2 to 2 months. All of the unvented roof assemblies are intolerant of incidental water leakage and the moisture-sensitive layers (i.e., sheathing and gypsum wallboard (for open-cell polyurethane insulation)) exceed the threshold for decay. In hot, humid climates, the most durable roof assemblies are the vented, open-cell polyurethane systems with shorter drying time of the interior gypsum wallboard when compared to the unvented roof assembly; both the sheathing and gypsum wallboard dry out within 2-1/2 months. In an unvented assembly, the drying time for sheathing is similar but the drying time for gypsum wallboard increases to 6.5 months on average. Alternatively, unvented permeable shingled roofs are a viable option in hot, humid climates, although they are slightly less durable. The least tolerant roof assemblies in either climate are the unvented closed-cell polyurethane roof assembly due to trapped moisture and slow drying of the roof sheathing (up to 12 months in Miami, FL and 27 months in Boston, MA).

Heat fluxes through roofs and their relevance to estimates of urban heat storage

The storage heat flux constitutes a large term in the heat balance of cities. This flux is difficult to measure but one approach is to parameterize it using relations between the net all-wave radiation and the heat flux conducted into and out of the typical materials that form the surface of cities and combine them into a weighted average to give the bulk storage. Urban heat storage parameterization could be improved if there were more and better estimates of the net radiation vs. storage relation for typical urban and suburban roofs. This paper presents the results of a study of the heat storage characteristics of 6 different roof assemblies (typical of many North American commercial/industrial and residential buildings) in Vancouver, Canada, observed across a range of wind and moisture conditions. Further, these observations are used to verify the Simplified Transient Analysis of Roofs ( STAR) model, which is then used to estimate the heat storage parameterization for other roof types, thereby extending the usefulness of the scheme to a wider range of urban areas.

A novel approach to estimate the wind uplift resistance of roofing systems

Roof wind design consist of three parts: determination of wind loads, evaluation of wind uplift resistance and correlating the resistance with the design load such that the resistance is higher than the load requirement. Wind uplift resistance of a system with its respective components is evaluated in laboratory testing. This paper presents a novel approach to estimate wind uplift resistance when components are substituted during field application. Wind dynamics, on a mechanically attached single-ply roofing assembly, lift the membrane and cause fluttering, introducing stresses at the attachment locations. In such assemblies, the fastener–deck interface is a critical design factor. First, by taking steel deck as a component this paper systematically characterizes the various steel decks that are commonly used in low slope application. Second component, namely the fasteners and its engagement strength with deck have been quantified for variations of its design, size and sources. Based on this component characterization, fastener pullout resistance (FPR) is identified as a verification factor for system wind resistance estimation. When variations occur in the fastener–deck interface between the proposed and the existing configurations, the present research through case studies has proved that: “ as long as the FPR of the proposed configuration is higher than the existing configuration then wind uplift ratings can be maintained”. This is valid as long as both the configurations have all the remaining roofing components similar with comparable layout. Based on this verification, the study recommends that the testing lab should report the FPR along with the wind uplift resistance such that FPR can be used as a verification factor to accept design/field alternatives.

Optimizing the Wind Uplift Resistance of Mechanically Attached Roof Systems

Wind dynamics on a mechanically attached single-ply roofing assembly can lift the membrane and cause fluttering, introducing stresses at the attachment locations. To identify a component in a system that has the weakest resistance against wind uplift forces, a dynamic evaluation method is beneficial. Over the past 10 years, a number of mechanically attached systems were constructed and exposed to simulated dynamic wind uplift forces using the Dynamic Roofing Facility at the National Research Council of Canada. This paper presents data from this ongoing investigation that will help system designers to maximize wind uplift ratings by choosing the appropriate roof components at the early design stage or by replacing/adding components during reroofing to improve uplift resistance. By diagnosing roof system failures, one can identify the weakest link and select design alternatives that can improve the wind resistance. Through a case study, this paper concludes with a procedure for system optimization.

Impact of air intrusion on the wind uplift performance of fully bonded roofing assemblies

Wind performance investigation is critical in the design of durable roofing assemblies. In North America, mainly two types of low slope roofs, conventional and inverted, are in practice depending on the placement of the membrane in the assembly. As part of the conventional low-sloped roofs, in a fully bonded assembly (FBA) the insulation is mechanically attached and waterproof membrane is bonded to the insulation using adhesives. Recent field investigations of roof failures after major hurricanes indicated that FBA are susceptible to high wind events. To understand the response of the FBA under dynamic environment, an extensive experimental study has been carried out by the SIGDERS – Special Interest Group for Dynamic Evaluation of Roofing Systems, at the National Research Council. The present study focuses on the impact of air intrusion on wind uplift performance of these assemblies. Airflow control is usually achieved by including a barrier/retarder in the roofing assembly. Assembly with barrier improved the wind uplift rating by two fold when compared to an assembly without barrier. Use of staggered insulation arrangement can provide similar air retarding effect as a barrier and can therefore sustain similar wind uplift pressures compared to an assembly with barrier.

Development of a New Test Method for Air Intrusion Quantification of Roofing Assemblies

Abstract In North America, approximately one-fourth of low-slope buildings are roofed with a mechanically attached assembly (MAA) with a single-ply membrane. During wind suctions, the membrane can lift and billow. This creates localized suction under the membrane. If design provisions are not made to control the air intruison at the deck level, this suction pressure can draw the indoor conditioned air into the assembly. Two main factors influence the air intrusion: the air permeability of the components and shape or volume changes during the wind uplift. Available standard test procedures can quantify the former for roof materials. However, there is no widely accepted standard specification or test to address the air intrusion characteristics of roofing assemblies. Air leakage measurement techniques used for walls are also not applicable for roof assemblies due to the membrane shape and volume changes in the roof assembly. Research efforts are under way at the National Research Council of Canada to quantify the air intrusion rate of roof assemblies. This paper presents the details of the experimental setup, test procedure, and validation effort of this newly developed test method.

Procedure for measuring the solar reflectance of flat or curved roofing assemblies

The widely used methods to measure the solar reflectance of roofing materials include ASTM standards E903 (spectrometer), C1549 (reflectometer), and E1918 (pyranometer). Standard E903 uses a spectrometer with an integrating sphere to measure the solar spectral reflectance of an area approximately 0.1 cm 2. The solar spectral reflectance is then weighted with a solar spectral irradiance to calculate the solar reflectance. Standard C1549 uses a reflectometer to measure the solar reflectance of an area approximately 5 cm 2. Both E903 and C1549 are best suited to measurement of the solar reflectance of flat, homogeneous surfaces. Standard E1918 uses a pyranometer to measure the solar reflectance of an area approximately 10 m 2, and is best applied to large surfaces that may also be rough and/or non-uniform. We describe a technique that uses a pyranometer to measure the solar reflectance of a uniform or variegated sample with diffusely reflective surface of an area of approximately 1 m 2, and use this technique (referred to as E1918A) to measure the solar reflectances of low- and high-profile tile assemblies. For 10 large (10 m 2) tile assemblies whose E1918 solar reflectances ranged from 0.10 to 0.50, the magnitude of the difference between the E1918A and E1918 measurements did not exceed 0.02 for unicolor assemblies, and did not exceed 0.03 for multicolor assemblies.