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• The study compares the thermal performance of green, white, and gravel roofs. • In-situ measurements monitor weather, roof surface temperatures, and heat flux. • Green roofs provide effective insulation for both winter and summer. • Heating and cooling energy needs are estimated for the different roof types. • Green roofs reduce total energy consumption in temperate climates. Roofs have been recognized as a potential area for intervention to achieve energy savings in buildings and enhance indoor comfort. In this context, green and cool roofs emerged as promising and attractive solutions for sustainable construction, offering various advantages, particularly in terms of the building's energy efficiency. However, their energy performance is closely tied to the local climatic conditions. This study presents a comparative analysis of the thermal and energy performance of four types of roofs − a green roof with sedum vegetation, a green roof with grass vegetation, a white painted roof, and a gravel-covered roof − under the temperate climate conditions of Poitiers, France. This comparative investigation helps to recommend optimal construction solutions tailored for temperate climates. Initially, in-situ measurements are conducted on two residential buildings equipped with these roof types. The experimental campaign involves monitoring weather conditions, roof surface temperatures, heat flux, and moisture content within the substrate layers of the green roofs. Subsequently, the TRNSYS software is employed to evaluate the heating, cooling, and total energy consumption of the investigated roof scenarios. The experiment results demonstrate that, in comparison to non-vegetated roofs, green roofs could maintain moderated outer surface temperatures. In summer, they effectively limit the entry of heat waves into the building, reducing heat flow by 52% for sedum and 71% for grass compared to the gravel roof. Furthermore, simulation results revealed that the grass green roof is the most effective solution for passive cooling, achieving energy reductions of 81 to 93% compared to other investigated roof types. Meanwhile, sedum vegetation emerges as the optimal choice for reducing total energy consumption, with reductions of up to 12% compared to the other roof type. [ABSTRACT FROM AUTHOR]

The shift towards using materials derived from plants is considered an innovative approach to creating eco-friendly buildings and decreasing the energy expenses associated with the building sector. This study aims to provide a comprehensive analysis of these materials' hygrothermal properties to support their successful integration in both new construction and building renovation projects. It reviews the current state of research on the thermal and hydric properties of plant materials on various scales: raw aggregate/fiber, plant-based composite, wall, and building scale. The first part focuses on the physical, chemical, and hygrothermal characterizations of raw plant aggregates and fibers. The second part covers the main hygrothermal properties of plant-based composites (insulation boards and concretes) and compares their performance with conventional materials. The study then shifts its focus to the hygrothermal performance of walls integrated with plant-based materials in response to external climate conditions. Finally, a review of full-size buildings is conducted to investigate the impact of these materials on hygrothermal behavior at the building scale and to highlight their influence on the reduction of energy consumption. A lack of studies on plant-based materials was observed. There remain numerous areas that require further investigation at each scale. Consequently, the study includes discussion sections that provide guidance for future research to fill the gaps and advance the development of this type of material. • Up-to-date literature on plant-based building materials at various scales is reviewed. • The physical, chemical, and hygrothermal properties of raw plant aggregates and fibers are discussed. • The hygrothermal properties of plant-based composites, insulation boards, and concretes are discussed. • The application of plant materials at the wall scale is reviewed. • The hygrothermal comfort and energy performance of plant-based composites at the building scale are highlighted. • Future studies are proposed to fully explore the potential of plants as sustainable building materials. [ABSTRACT FROM AUTHOR]

The study of wood behaviour in the event of fire is of increasing interest in the civil engineering field. Wood is one of the most prevalent combustible materials used in buildings. However, this material is protected by the char layer during fire exposure. It can slow down the charring rate of timber in fire and protect the internal wood structure. In fire tests, it is very important to use the most effective method of measuring the temperature of wood. In this paper, experimental tests are performed in furnaces and the charring rate is determined by measuring the depth of the charred part of timber at the end of the time. This approach is compared to direct measurements given by thermocouples positioned at different depths in the wood sample in different directions (radial, longitudinal, and tangential). All test samples were tested in a furnace where three surfaces of the sample were exposed to ISO-834 fire standards. The comparison between the two methods of measuring the charring rate allowed us to evaluate the accuracy of the thermocouple measurements according to the implementation adopted in the sample. Besides, the factors affecting the temperature measurement results are also mentioned in this study such as the position of the thermocouple in the wood, the size of the measuring sample and the size of the thermocouple. [ABSTRACT FROM AUTHOR]

• The thermal behaviour of hybrid steel-timber elements was evaluated through experimental tests and numerical modelling. • The wood provides significant protection to the steel cross-section mainly the fully encapsulated IPE profile. • The wood is performed as insulating material that significantly reduces the temperature rise in steel. • The experimental results are compared to those obtained through thermal simulations using Abaqus software. • The proposed numerical model can be used to evaluate the temperature increase in the steel element protected by timber in high-temperature conditions. Steel-timber hybrid structures are becoming more and more common in the construction industry. They offer high practical advantages as sustainable solutions with high load-bearing capacities and fire resistance. Wood is occasionally used as a passive protection for steel to maintain its mechanical strength as long as possible with the aim to prevent structural collapse under fire. This paper aims to analyse the thermal behaviour of hybrid steel-timber elements through experimental tests and numerical modelling. The fire tests were performed on various steel-timber combinations using T and I steel cross-sections with various wood species. A high-temperature furnace of up to 1200 °C built in the laboratory was used. The results show that wood provides a significant protection to the steel cross-section, mainly to the fully encapsulated IPE profile. Wood performed as an insulating material that significantly reduced the temperature rise in steel. The experimental results are compared to those obtained through thermal simulations using Abaqus software. The comparison shows that the numerical model can be used to evaluate the temperature increase in the steel element protected by timber in high-temperature conditions. [ABSTRACT FROM AUTHOR]

In order to better predict the hygrothermal behavior of porous building envelopes, it is essential to develop reliable mathematical models which accurately capture the coupled heat, air, and mass (HAM) transport and its influence on the indoor atmosphere. Recently, numerous models have been developed to predict the performance of bio-based building envelopes. However, the large number of input parameters and lack of knowledge of the intrinsic characteristics of the materials mean these models are quite difficult to implement. To determine the most influential hygrothermal parameters for a hemp concrete wall, a sensitivity study was conducted on the input parameters, based on the probability density distribution of Gaussian centered law; the results are presented herein. A reduced model was developed by eliminating the parameters with little or no influence on HAM transfer. Then, a dimensionless study of the reduced model was carried out. This generated an indicative parameter ς, which can be used to classify building materials and identify the most suitable. In MATLAB software, the simulated results for a hemp concrete wall showed satisfactory concordance with the experimental results found in the literature. The temperature profiles are accurately estimated. Note that the model must always take account of the evolution of water content to ensure accurate RH predictions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Evaporation and transpiration were evaluated separately. [•] The thermal resistance of green roofs was evaluated using a low-speed wind tunnel. [•] The impact of grey water on evapotranspiration and green roof thermal resistance was studied. [ABSTRACT FROM AUTHOR]

Highlights: [•] The experimental platform provides the hydrothermal behavior data for green roof. [•] The albedo of the green roof was measured and implemented in the numerical model. [•] A coupled heat and mass transfer model for green roof behavior was validated. [•] Comparison was undertaken between green and conventional roofing. [•] Green roofing reduces energy demand and outside air temperature in canyon streets. [Copyright &y& Elsevier]

• Microscopic structure characterization of straw fibers. • Thermal and mechanical properties of straw bales. • Fire and sound resistance of a straw bale walls. • Life cycle assessment of a straw construction. • Energy and economic performance of straw bale buildings. Bio-based materials such as straw are becoming a promising alternative to improve the building energy performance and to reduce its carbon footprint. When compared to common building construction materials, bio-based materials control the temperature and the relative humidity variation to ameliorate the indoor comfort with a low embodied energy and CO 2 emission. This paper presents a comprehensive review of the thermal and mechanical properties of straw-based materials and buildings. The objective is to synthesis the work that has been carried out by the research community and to compare the results. The paper first introduces straw bale as a construction material from a historical viewpoint and in the context of the current building sector. The second part focuses on the available chemical and microstructural data of the straw fiber. The third part refers to the thermophysical and mechanical properties of the bales. The fourth part reviews the numerical and experimental studies done at the wall scale. The fifth part describes straw bale construction methods considering the regulation, structure requirements, and life cycle assessment data. Last, a critical analysis of the currently available data on straw as a building material is carried out and pending research issues are discussed. It was found that, despite abundant literature on structural and thermal properties of straw bale constructions, there is still a lack of some information. At a fiber scale, more research should be done to compare straw fibers to other natural and synthetic fibers. At a bale scale, further pH-related research is needed because it affects the material's interior conditions and durability. In addition, a thermal conductivity model for straw should be developed. On a bigger scale, the hygrothermal characteristics of various types of walls must be measured and computed experimentally and theoretically under various exterior and internal situations. More research is needed to improve the sound resistance of the straw wall by adding new layers capable of absorbing acoustic waves. Studies on the energy behavior, cost analysis, and how interior air moisture is self-regulated in straw buildings are needed at the building size. Therefore, a lack of consistent data among the different studies was noted depending on the straw characteristics. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes a dynamic model of transient heat and mass transfer across a green roof component. The thermal behavior of the green roof layers is modeled and coupled to the water balance in the substrate that is determined accounting for evapotranspiration. The water balance variations over time directly impact the physical properties of the substrate and the evapotranspiration intensity. This thermal and hydric model incorporates wind speed effects within the foliage through a new calculation of the resistance to heat and mass transfer within the leaf canopy. The developed model is validated with experimental data from a one-tenth-scale green roof located at the University of La Rochelle. A comparison between the numerical and the experimental results demonstrates the accuracy of the model for predicting the substrate temperature and water content variations. The heat and mass transfer mechanisms through green roofs are analyzed and explained using the modeled energy balances, and parametric studies of green roof behavior are presented. A surface temperature difference of up to 25°C was found among green roofs with a dry growing medium or a saturated growing medium. Furthermore, the thermal inertia effects, which are usually simplified or neglected, are taken into account and shown to affect the temperature and flux results. This study highlights the importance of a coupled evapotranspiration process model for the accurate assessment of the passive cooling effect of green roofs. [Copyright &y& Elsevier]

Abstract: Green roofs have several environmental benefits, such as improving building energy efficiency. The present paper provides a comprehensive study of the impact of a green roof on building energy performance. A model of green roof thermal behavior was coupled with a building code to allow the evaluation of green roof foliage and soil surface temperatures. Simulations were conducted for a single-family house with conventional and green roofs in a temperate French climate. In the summer, the fluctuation amplitude of the roof slab temperature was found to be reduced by 30°C due to the green roof. The heat flux through the roof was also evaluated. In the summer, the roof passive cooling effect was three times more efficient with the green roof. In the winter, the green roof reduced roof heat losses during cold days; however, it increased these losses during sunny days. The impact of the green roof on indoor air temperature and cooling and heating demand was analyzed. With a green roof, the summer indoor air temperature was decreased by 2°C, and the annual energy demand was reduced by 6%. The present study shows that the thermal impact of green roofs is not functionally proportional to the leaf area index parameter. It also shows the high dependency of this impact on the roof insulation. Finally, the simulations suggest that green roofs are thermally beneficial for hot, temperate, and cold European climates. [Copyright &y& Elsevier]

Straw bale building construction is attracting a revived public interest because of its potential for reduced carbon footprint, hygrothermal comfort, and energy savings at an affordable price. The present paper aims to summarize the current knowledge on straw bale construction, using available data from academic, industry, and public agencies sources. The main findings on straw fibers, bales, walls, and buildings are presented. The literature shows a wide variability of results, which reflects the diversity of straw material and of straw construction techniques. It is found that the effective thermal conductivity, density, specific heat, and elastic modulus of straw bales used in construction are in the range 0.033–0.19 W/(m·K), 80–150 kg/m3, 1075–2000 J/(kg·K), and 150–350 kPa respectively. Most straw-based multilayered walls comply with fire resistance regulations, and their U-value and sound reduction index range from 0.11 to 0.28 W/m2 K and 42 to 53 dB respectively, depending on the wall layout. When compared to standard buildings, straw bale buildings do provide yearly reductions in carbon emissions and energy consumption. The reductions often match those obtained after applying energy-saving technologies in standard buildings. The paper ends by discussing the future research needed to foster the dissemination of straw bale construction. [ABSTRACT FROM AUTHOR]

• The interconnections distribution in fibers determines the heat transfer model. • The development of a thermal conductivity equation considers the radiative heat transfer. • The bale's thermal conductivity varies according to the fiber orientation. • Thermal conductivity depends on the chemical composition of the straw. Straw fibers are natural fibers that have a strong insulating property and a minimal environmental effect, making them suitable construction materials. In the construction sector, to predict the building energy consumption, the thermal conductivity of the materials composing the envelopes must be precisely known, which is not the case for the straw material. The properties of a straw bale are variable and mainly depend on its density, fibers orientation, chemical composition, temperature and relative humidity. Consequently, this study consists of determining a mathematical equation to predict the effective thermal conductivity of straw bales that can be applied to all straw types, in different circumstances. For this purpose, the size, distribution, and morphology of straw fibers are first determined from microscopic images. Second, a mathematical model for estimating the thermal conductivity is suggested using the heat transfer models of porous and fibrous materials. The numerical model is validated by an experimental study that measures the thermal conductivity of straw bales by altering their density between 80 and 120 kg/m3, their relative humidity between 15 % and 95 %, and their temperature between 15 ˚C and 55 ˚C. The experimental results show that the thermal conductivity increases from a minimum of 0.047 W/(m∙K) to a maximum of 0.09 W/(m∙K) when increasing the three altered factors. For a straw fiber having 40% cellulose content, the thermal conductivity increased from a minimum of 0.05 W/(m∙K) to a maximum of 0.0832 W/(m∙K). This behavior is found the same for the numerical findings. The comparison of numerical and experimental values shows a good agreement, with a root mean square error of 0.005 W/(m∙K) and a scatter index of 5.5 %. [ABSTRACT FROM AUTHOR]

• The temperature and relative humidity variations obtained by WUFI are in good agreement with the literature experimental findings. • The excessive moisture content in straw leads to bio-deterioration, mold, and decay damage in the whole structure. • The hygrothermal issues in a straw wall depend on the interior and exterior covering layers. • Hygrothermal issues can be solved by adding the straw thickness, adding a vapor retarder layer, adding an unventilated air layer, and controlling the indoor conditions. Straw is becoming a promising alternative insulation material to improve the building energy performance because of its low cost, large availability as cereal waste, its good hygrothermal properties, and its low embodied energy. The goal of this paper is to assess the hygrothermal performance of multi-layered straw walls with different boundary conditions. The study consists of evaluating five different straw-based wall assemblies, under a continental (Arkhangelsk, Russia), a tropical climate (Brasilia, Brazil), a temperate Mediterranean climate (Nice, France), and a cold desert climate Xinjiang (China). Numerical models of the heat and moisture transfer through the walls using WUFI software are developed, calibrated, and validated through experimental results from the literature. The chosen evaluation criteria are the total water content, the drying rate, the condensation risk, the mold growth, the moisture quantity, the time lag, and the decrement factor. Results show that straw walls with cement and/or wood covering can be used in tropical and temperate climates, coated straw walls with additional air layers in dry climates, while insulated straw walls are best fitted in continental climates. In the latter, the dryness rate varies between 7 and 40% with a low condensation risk of value in the range of 0–12%. It can be concluded that the straw wall's performance strongly depends on the interior and exterior added thermal insulation layers since they affect the ability of the material to dry out. [ABSTRACT FROM AUTHOR]