Roof Assemblies Research Articles

Factors to Consider in Developing Conceptual Scopes of Repair for Common Low-Slope Roofing Assemblies

Forensic engineers are commonly asked to develop conceptual scopes of repair as part of their work. Many factors impact these recommendations, including building codes, construction feasibility, manufacturer assessment, and installation requirements. In addition, the conditions present on and within the existing roof surfaces can limit the repairability of a commercial roof assembly such that removal and replacement of the entire roof section is the appropriate or only feasible repair option. This paper will focus on common limitations to be considered when developing a conceptual scope of repair for common commercial roof systems, including single-ply membranes, built-up roofing, metal panel roofing, spray polyurethane foam roofing, and the application/maintenance of roof coatings. It will also discuss an assessment methodology that can assist in developing a broader understanding of the condition of the roof surfaces.

Thermal Performance of Residential Roofs in Malaysia: Experimental Study Using an Indoor Solar Simulator

Previous researchers have detailed the problems in measuring the thermal resistance value of a whole roof assembly under hot conditions due to the uncertainty of the outdoor environment. Currently, no established method exists to experimentally investigate an entire thermal roof performance under a steady-state condition. This article details the properties of the indoor solar simulator and the research methods undertaken to measure the thermal resistance value of roof assembly. The indoor solar simulator utilizes 40 halogen bulbs to accurately replicate sun radiation. Thermocouples and heat flux sensors are installed at several locations on the roof assembly to quantify the heat transmission occurring through it. The thermal resistance value is determined by adding up the average difference in temperature across the external and internal roof surfaces and dividing the total amount by the total of all averaged heat fluxes. Subsequently, this study investigates the thermal efficiency of residential roof assemblies that comprise various insulation materials frequently employed in Malaysia, including stone wool, mineral glass wool, reflective bubble foil insulation, and radiant barriers. The analysis showed that the roof configurations with bubble foil reflective insulation produce superior thermal resistance values when coupled with enclosed air space or mass insulation, with thermal resistance values ranging between 2.55 m2K/W and 3.22 m2K/W. It can be concluded that roof configurations with bubble foil reflective insulation resulted in high total thermal resistance and passed the minimum thermal resistance value of 2.5 m2K/W under the Malaysian Uniform Building By-Law 38 (A) requirements. Furthermore, the radiant barrier produced a high thermal resistance value of 2.50 m2K/W when installed parallel to a 50 mm enclosed air space, emphasising the crucial function of an enclosed air space next to a reflective foil to resist the incoming heat radiation. The findings from this research can help building professionals determine the optimum insulation for residential building roofs in Malaysia.

RELATIONSHIPS BETWEEN EMBODIED, OPERATIONAL, AND LIFE CYCLE CARBON IN PASSIVE HOUSE MULTIFAMILY RESIDENTIAL BUILDINGS

ABSTRACT The building sector is responsible for a significant portion of global CO2 emissions and any attempt to meet global climate change mitigation goals requires dramatic reductions in CO2 emissions from building construction and use. Among the many green building certification programs intended to reduce the environmental impact of buildings, the passive house standards are one of the most stringent certifications with respect to reducing operational energy. While there is significant research demonstrating the reductions in operational energy use in passive house and passive house inspired buildings, there is comparatively little research into the embodied energy and embodied carbon emissions associated with these buildings. The aim of this research was to evaluate the relationship between embodied carbon emissions, operational carbon emissions, and overall carbon use intensity in passive house certified residential buildings, using a recently completed, multifamily passive house as a case study. First, the case study building was defined, and a partial life cycle assessment (LCA) was performed to evaluate the embodied and operational carbon emissions associated with this base case. Second, a catalog of alternative wall and roof assemblies were defined and the LCA of the case study was updated for each alternative assembly to assess the impact on the embodied carbon, operational carbon, and overall carbon use intensity. The results of this analysis indicate that the material composition of the exterior envelope assemblies can have significant impact on the overall, cumulative carbon impact of a particular building. Moreover, the results also indicate that there are clear scenarios in which operational energy efficiency should be sacrificed in favor of reducing upfront embodied carbon emissions, particularly when evaluated over critical time spans. Based on these results, this study recommends that green building standards and certifications, including passive house but also USGBC LEED, Living Building Challenge, and others, should place greater emphasis on embodied carbon and holistic carbon accounting in addition to operational efficiency.

Forensic Analysis of Roof Deterioration Due to Condensation

Corrosion of the structural steel roof deck of large warehouses resulted in several invasive forensic investigations to determine the cause and mechanism of the corrosion. The warehouse roof investigation presented in this paper is one of many similar warehouses located near the Gulf of Mexico and along the Southern Atlantic Seaboard experiencing corroded roof decks when constructed using fiberboard roof insulation made from sugarcane fiber called bagasse. Consensus exists among individuals studying this phenomenon that the fiberboard became saturated with water, which dissolved formic and acetic acid from the fiberboard. The steel deck corroded when it came in contact with the acidic solution. There was little consensus regarding the mechanism by which water intruded into the roof assembly. Invasive investigation of the low-slope roofs of buildings with various types of insulation (including bagasse fiberboard) and observation of physical commonalities between the instances led to the following conclusion: Water in the roof assemblies did not result from leaks through a compromised roof membrane but rather from humid air infiltrating the roof assembly and condensing on the underside of the roof membrane.

A strategy for lightweight designing of a railway vehicle car body including composite material and dynamic structural optimization

AbstractRolling stock manufacturers are finding structural solutions to reduce power required by the vehicles, and the lightweight design of the car body represents a possible solution. Optimization processes and innovative materials can be combined in order to achieve this goal. In this framework, we propose the redesign and optimization process of the car body roof for a light rail vehicle, introducing a sandwich structure. Bonded joint was used as a fastening system. The project was carried out on a single car of a modern tram platform. This preliminary numerical work was developed in two main steps: redesign of the car body structure and optimization of the innovated system. Objective of the process was the mass reduction of the whole metallic structure, while the constraint condition was imposed on the first frequency of vibration of the system. The effect of introducing a sandwich panel within the roof assembly was evaluated, focusing on the mechanical and dynamic performances of the whole car body. A mass saving of 63% on the optimized components was achieved, corresponding to a 7.6% if compared to the complete car body shell. In addition, a positive increasing of 17.7% on the first frequency of vibration was observed. Encouraging results have been achieved in terms of weight reduction and mechanical behaviour of the innovated car body.

Development of an indoor solar simulator for the evaluation of the thermal roof performance for commercial buildings in Malaysia

Past researchers have expressed the difficulty in assessing the empirical thermal performance of an entire roof assembly in terms of thermal resistance (RSI value) under hot conditions. This research discussed the development of an indoor solar simulator to assess the thermal performance of commercial building roofs under steady-state conditions. The indoor solar simulator has 40 halogen lamps to simulate solar radiation. Thermocouples and heat flux transducers are mounted at various points across the roof assembly to measure the heat transfer through the roof assembly. From the error analysis, the RSI values obtained experimentally using the indoor solar simulator and ASHRAE Standard agree with a MAPE value of 6.13%. This paper compares the thermal performance of radiant barriers, bubble foil reflective insulation, polyurethane (PU) foam, and mineral glass wool in a roof assembly. The measurement results showed that the radiant barrier and bubble foil reflective insulation has high RSI values ranging from 1.22 m2K/W to 2.19 m2K/W for enclosed air gap thicknesses from 25 mm to 125 mm. In contrast, the metal deck roof with PU metal resulted in RSI values from 0.55 m2K/W to 1.62 m2K/W for PU thicknesses from 20 mm to 50 mm. The combination of radiant barrier and glass mineral wool of 50 mm and 100 mm resulted in RSI values of 0.83 m2K/W and 1.60 m2K/W, respectively. The results from this research can be used to identify the optimum insulation for different roof configurations commonly used in the Malaysian building industry.

Measured noise levels beneath type B flat metal roof assemblies during rainfall

Flat metal roof assemblies are common in steel building design. Since they can produce high levels of rainfall generated noise, quiet roof assemblies are desirable over noise sensitive spaces. To determine the relative effects of assembly variations, a pair of fixtures were constructed to measure the noise levels beneath 2 x 4 ft sections of selected roof assemblies subjected to rainfall. Each test item was assembled from precut 2 x 4 ft sections of Type B metal roof (with or without a concrete layer), cover boards, and insulation, membrane and ballast as required. The fixtures were equipped with tipping buckets to measure rainfall rate. A microphone located inside each box and connected to a digital recorder, picked up ambient noise, rainfall generated roof assembly noise and the tipping bucket signal. To calibrate the recordings, the sound pressure level of the tipping bucket signal at the recording microphone was measured before testing. Recordings were analyzed to calculate indicated octave band sound power levels versus rainfall rate for the various tested roof assemblies.

Impact of Solar Mounting Systems on the Thermal Design of Commercial Roofs

Commercial rooftops provide extensive areas representing the desired platform for installing photovoltaic (PV) systems. The combination of roofing assembly and PV system is called photovoltaic roofing assembly (PVRA). Currently, there is a shortage of information about building codes on PV system and roofing assembly integration. The National Research Council of Canada (NRC) developed an industry consortium project to generate codifiable research data on the wind and thermal performances of photovoltaic roofing assemblies. This paper examines the thermal bridging of the PV mounting attachments and its impact on the overall thermal resistance of the roofing assembly. Seven different types of PV mounting fixed attachments were tested in this study. Thermal bridging evaluation of PV mounts was done on the component level as individual mounts were installed through a section of a roofing assembly. The roofing assemblies were designed for a prescriptive thermal resistance of RSI 5.46 m2 K W−1 (R-31 h ft2 °F BTU−1) as per current standard and requirements for Climate zones 4–6. The thermal bridging experiments were conducted on a 1.2 m by 1.2 m guarded hot box at a mean temperature of 24°C. The measured data indicated a decrease in the effective thermal resistance of the PVRA, ranging from 3.3% to 50.0%, compared to the opaque roofing assembly devoid of any thermal bridging. Furthermore, it was found that among fastener-designed PV mounting attachments, the greater the number of fasteners, the more significant the decrease in effective thermal resistance. From the experimental data, chi factors (χ) were developed to support the calculation of point thermal bridging effects on the thermal performance of low-sloped roofing assemblies. Toward codification, efforts are underway to potentially implement these chi factors in the energy codes that could enhance the thermal design of both retrofit and new roof constructions installed with photovoltaic systems.

Measured noise levels beneath type B flat metal roof assemblies during rainfall

Flat metal roof assemblies are common in steel building design. Since they can produce high levels of rainfall generated noise, quiet roof assemblies are desirable over noise sensitive spaces. To determine the relative effects of design variations, a pair of fixtures were constructed to measure the noise levels beneath 2 × 4 ft sections of selected roof assemblies subjected to rainfall. Each test item was assembled from precut 2 × 4 ft sections of type B metal roof (with or without a concrete layer), cover boards, and insulation, membrane and ballast as required. The fixtures included a tipping bucket to measure rainfall rate. A microphone located inside each fixture and connected to a digital recorder, picked up ambient noise, rainfall generated roof assembly noise, and the tipping bucket signal. To calibrate the recordings, the sound pressure level of the tipping bucket signal was measured at the recording microphone before testing. Recordings are analyzed to calculate indicated octave band sound power levels versus rainfall rate for the various tested roof assemblies. Promising variations for further study are given.

Thermal performance of reflective insulation system and comparison against ASHRAE Standard

The trend in building energy consumption has been steadily increasing and will continue to rise significantly in the future. The application of a reflective insulation system in roof assembly is proven to be effective in reducing heat gain across the roof and can enhance indoor thermal comfort. This paper presents the development of an Indoor Solar Simulator to evaluate the thermal resistance (RSI value) of reflective insulation systems for roof assemblies. This paper also compares RSI values obtained experimentally and the RSI values listed in ASHRAE Standard. The roof assemblies studied in this paper incorporate the same reflective insulation systems as listed in ASHRAE Standard. Thermocouples and heat flux transducers are installed at various locations and the RSI values are calculated using the average method as detailed in ISO 9869-1:2014. From the error analysis, it can be concluded the RSI values obtained experimentally using the Indoor Solar Simulator and ASHRAE Standard are in a good agreement with MAPE value of 6.13%. These discrepancies could be due to the thermal bridges from mechanical supports inside the air gap, or possibly the air gaps are not completely airtight and unventilated.

Dynamic size optimization approach to support railway carbody lightweight design process

The transition to a globalised electrical power supply pushes rolling stock manufacturers to find structural solutions for reducing the power required by the vehicles. Within a market where details can make the difference in economic terms, the concept of design optimization is becoming established. However, current industrial procedure for the evaluation of carbody structural strength, in static field and according to EN 12663-1:2015 standard, does not include any optimization process. More in general, optimization processes, and especially dynamic optimization, are not widely used for designing of railway vehicles. In this framework, the present paper proposes a new dynamic optimization approach to support the design of railway vehicle carbodies subjected to static loads. Proposed methodology aims to minimize the mass of the metallic structure, working on the thicknesses of the optimized components, maintaining the baseline geometry. The constraint function was imposed on the first natural vibration frequency of the system. The optimization strategy is based on a dynamic size optimization process in conjunction with modal analysis techniques, applied on the single carbody shell. The procedure has involved the roof assembly of a single tram vehicle body. The proposed approach is resulted numerically efficient in terms of calculation times. Encouraging results have been achieved in terms of mass saving and mechanical behaviour of the carbody shell. Optimized components were 21% lighter than the original, that corresponds to 3% if evaluated on the total mass of the single carbody metallic structure. The methodology turns out to be a useful tool for supporting designers to reduce the mass of the carbody structures, reducing overdimensioning condition that could affect the carbody structure.

Determining the Vapour Resistance of Breather Membrane Adhesive Joints.

Due to increasingly stringent requirements, tapes and adhesive joints are a commonly used method to ensure tightness and energy efficiency in modern building envelopes. Previous studies have researched and tested properties such as the strength and tightness of adhesive joints. So far, water vapour resistance has been neglected. This article aims to determine the vapour resistance and shed light on possible consequences of vapour-tight adhesive joints in breather membranes used in roof assemblies. Laboratory measurements of vapour resistance were conducted according to NS-EN ISO 12572:2016, known as the cup method. Eleven products of breather membranes were tested. Results from the laboratory measurements were used to evaluate the impact of vapour-resistant adhesive joints related to the drying of built-in moisture. The simulation programs WUFI 2D and WUFI Mould Index VTT were used to model scenarios for moisture transport and risk for mould growth. Laboratory results show that the vapour resistance of breather membrane adhesive joints varies from 1.1 to 32 m in sd-value. Three of the tested products have a vapour resistance larger than 10 m, while four products have an sd-value less than 2.0 m. The sd-values of the membranes themselves range between 0.027 and 0.20 m. All tested adhesive joints are considerably more vapour tight than the Norwegian recommended value for breather membranes (<0.5 m). However, the mould growth analysis shows that the risk of mould growth is low in most practical cases, except when using adhesive joints with the highest vapour resistance in roofs assembled during autumn.

Design and Experimental Analysis of Connections for a Panelized Wood Frame Roof System

This paper presents the results of an experimental study on the short-term mechanical performance of timber screw connections comprising two types of fasteners suitable for a novel panelized roof design process. Thirty-seven specimens of five different connection configurations were tested under quasi-static monotonic loading. The main objective of this study is to provide a preliminary assessment of connection capacity that is key to the successful implementation of a proposed panelized roof design method. It also provides the basis to assist in the development of a numerical model of the novel roof assembly. Additionally, the experimental data are used to check the validity of existing analytical approaches for predicting the strengths of screwed connections comprising engineered wood members. The validation exercise shows that available analytical models can be used to predict the connection capacity of the novel panelized roof.

Development of a New Dynamic Test Method to Determine the Wind Pressure Resistance of Photovoltaic Roof Assembly (PVRA)

Abstract Commercial rooftops provide extensive areas that represent the ideal platform to install a photovoltaic (PV) system. The combination of the roofing assembly and the PV system is termed a photovoltaic roofing assembly (PVRA). There was little guidance for determining the wind loads on rooftop PV systems for many years. With the efforts of the Structural Engineers Association of California and numerous wind tunnel studies conducted by reputed labs, the design methodology for determining wind loads on PV systems has been established, which has become ASCE 7-16, Minimum Design Loads for Buildings and Other Structures, and the National Building Code of Canada 2015. However, there is no guidance on the resistance aspect of the PVRA. During the life cycle of the rooftop solar array, the variable amplitude of the dynamic wind loading can lead to fatigue, which can accumulate damage in structure details. Such damages might lead to severe failures in the whole PVRA. Currently, there are no standardized test methods that determine the collective performance of a PVRA. In collaboration with the roofing and solar industry, the National Research Council Canada (NRC) is conducting a research study to address the missing link between the design and resistance of a PVRA. A unique, dynamic test method was developed to determine the wind pressure resistance of a PVRA. The test methodology applies uniform wind pressure on a 3 × 3 array. It provides a complete load path evaluating the capacity in members, connections, and PV attachments to the roof assembly. The current paper presents the PVRA test apparatus commissioning process. It details the experimental apparatus, the definition of the testing specimen, the establishment of a dynamic loading protocol, and quantification (measurements) of the system response. It also presents the results of pilot testing conducted as per the new test method. Once standardized, this new protocol will ensure that PVRA integrity is maintained and PV performance is optimized.

Thermal-Energy Performance of Bulk Insulation Coupled with High-Albedo Roof Tiles in Urban Pitched Residential Roof Assemblies in the Hot, Humid Climate

The high rate of heat transfer through the residential roof assembly aggravates the condition of indoor thermal discomfort. Bulk insulation can be installed in the assembly to improve thermal performance. However, although it can efficiently reduce diurnal heat transfer from the outdoor environment into the indoor space through the roof assembly, it can also suppress nocturnal heat transfer in the opposite direction. Alternatively, high-albedo roof tiles employ cool colors to reflect heat at the roof surface, whereas bulk insulation hinders the conduction of heat through the roof assembly. In light of the potential of high-albedo roof tiles and bulk insulation in reducing heat transfer, thermal-energy performance of an urban pitched residential roof assembly, which adopted varying configurations of high-albedo roof tiles and bulk insulation under a hot, humid climate, was evaluated. Energy savings were generated, which were 15.13% when the change from a conventional to a high-albedo roof surface was performed, and 17.00% when the installation of bulk insulation was performed on the high-albedo roof assembly.

COMPUTATIONAL ANALYSIS OF A BUILDING: AN ENERGY-EFFICIENT APPROACH USING EQUEST CODE

t— Building energy demand increases gradually as the urbanization advances. Energy consumption due to space cooling is a crucial area of research. Researchers around the globe, attempt to replicate the energy behaviour of building using numerous types of simulation tools. In this study, a model of an engineering college has been considered for analysis of energy consumption throughout a year. This article explores various factors affecting overall energy demand of a building which is located in the hot and dry climate of Bikaner (28.0229 °N, 73.3119 °E), India. An air-cooled chiller is modelled in eQuest, which is a building modelling and simulation tool, to meet the space cooling requirement of the building and a baseline model in eQuest is created in compliance with ASHRAE 90.1 and Energy Conservation Building Code (ECBC), Government of India. The impact of different building orientations and construction of roof assemblies on energy utilization is investigated. A lucid impact of aforementioned parameters on building energy requirement is observed which turns into a considerable saving in annual energy consumption up to 3.36%.

Development of Psi Factors for Thermal Bypass Due to Insulation Gaps in Low-Slope Roofing Assemblies

In commercial roofs, the presence or formation of gaps could be due to improper installation, thermal expansion, and dimensional changes in the insulation boards. The heat loss from these gaps could lead to higher thermal transmittance in the roof assembly. The current research study conducted around 70 experiments to investigate the effect of gap height, gap width and gap offset on the thermal transmittance of the roofing assembly. The measured data showed that in a staggered insulation layout with a joint offset of 610 mm (24 in), formation of 6.4 mm (1/4 in) to 12.7 mm (1/2 in) gaps at the insulation joints could contribute to an average decrease of 2% to 9% in the effective R-value of the roof assembly. As the insulation thermal resistance increases or becomes thicker, the thermal losses in the roof assembly increase. Generalized gap impact curves were developed to provide the relation between gap parameters (i.e., gap widths and height) and the thermal performance of the roof assembly. The experimental data were further analyzed using the psi factor approach of linear thermal bridging generating thermal transmittance data to support the calculation of thermal bypass from gaps in the thermal roof design.

TYPES OF FLAT EARTHEN ROOFS USED IN VERNACULAR ANATOLIAN ARCHITECTURE AND THEIR PRESERVATION PROBLEMS

ABSTRACT Earthen materials and rammed earth architecture concepts are becoming more and more popular among architects due to their applicability in various climates and low-cost construction technique. However, the use of flat earthen roofs in today’s architecture is rare, although there is historical evidence for the vernacular use of earthen materials in roof assemblies. The first examples for vernacular earthen flat roofs are found in Anatolia, Catalhoyuk. Flat earthen roofs used in vernacular, Anatolian buildings should be studied because a lack of maintenance has resulted in these vernacular Anatolian earthen buildings being on the verge of extinction today. There is a lack of literature research about the construction materials and techniques used in this traditional construction process. The aim of this study is to compile and present the knowledge behind this traditional flat earthen roof technique. In this study, initially, the flat earthen roofs used in vernacular Anatolian Architecture are analyzed via an extensive literature review. It has been found that in different districts of Anatolia, different types of vernacular flat earthen roofs together with different material layers and construction techniques exist. Site studies were carried out in Kemaliye.* During these site studies, six flat earthen roofs present in Kemaliye and in neighboring towns constructed via traditional construction techniques were analyzed and interviews were carried out with seven local foremen. Then, based on the information gathered, these traditional flat earthen roofs were classified into four types according to their material layers and construction techniques. Finally, preservation problems for flat earthen roofs are discussed.

TYPES OF FLAT EARTHEN ROOFS USED IN VERNACULAR ANATOLIAN ARCHITECTURE AND THEIR PRESERVATION PROBLEMS

ABSTRACT Earthen materials and rammed earth architecture concepts are becoming more and more popular among architects due to their applicability in various climates and low-cost construction technique. However, the use of flat earthen roofs in today’s architecture is rare, although there is historical evidence for the vernacular use of earthen materials in roof assemblies. The first examples for vernacular earthen flat roofs are found in Anatolia, Catalhoyuk. Flat earthen roofs used in vernacular, Anatolian buildings should be studied because a lack of maintenance has resulted in these vernacular Anatolian earthen buildings being on the verge of extinction today. There is a lack of literature research about the construction materials and techniques used in this traditional construction process. The aim of this study is to compile and present the knowledge behind this traditional flat earthen roof technique. In this study, initially, the flat earthen roofs used in vernacular Anatolian Architecture are analyzed via an extensive literature review. It has been found that in different districts of Anatolia, different types of vernacular flat earthen roofs together with different material layers and construction techniques exist. Site studies were carried out in Kemaliye.* During these site studies, six flat earthen roofs present in Kemaliye and in neighboring towns constructed via traditional construction techniques were analyzed and interviews were carried out with seven local foremen. Then, based on the information gathered, these traditional flat earthen roofs were classified into four types according to their material layers and construction techniques. Finally, preservation problems for flat earthen roofs are discussed.

Thermal-Energy Performance of High-Albedo Roof Tiles and Bulk Rafter Insulation in Residential Roof in the Tropical Climate

Residential roof assemblies in tropical countries, such as Malaysia, are exposed to intense solar radiation throughout the day all-year round due to the high altitude of the sun path as well as the horizontal orientation and high position of the roof in relation to other components of the building envelope. Residential buildings typically employ a lightweight pitched roof with roof tiles and an attic space above a ceiling board. Diurnal heat transfer into the building through the roof assembly can be minimized by reflecting heat at the roof surface via the application of white paint on high-albedo roof tiles as well as resisting heat via installation of bulk rafter insulation within the roof assembly. However, their adoption will have an influence on the nocturnal heat transfer and, accordingly, the resultant thermal-energy performance. Hence, thermal-energy performances of high-albedo roof tiles and bulk rafter insulation were compared to develop an energy-efficient pitched residential roof assembly that is capable of minimizing diurnal heat transfer into the building with less obstruction of the nocturnal heat transfer in the opposite direction. Evaluation of thermal-energy performance was performed on a Building Information Model, which either adopts, solely, the application of white paint on high-albedo roof tiles, or, in amalgamation with, the installation of bulk rafter insulation within the roof assembly. The simulation projected that the application of white paint on high-albedo roof tiles can generate annual energy savings of 13.14 % and, when adopted in amalgamation with the installation of bulk rafter insulation within the roof assembly, 13.91 %.