Roof Layers Research Articles

Performance Analysis of rooftop greenery systems in Australian subtropical climate

This paper presents the performance analysis of an extensive rooftop greenery system (green roof) in buildings in the Australian Subtropical climate, both experimentally and computationally. The impact of green roof systems on building thermal performance, energy consumption and energy savings are examined and compared with a non-green roof system in both experimentally and using computer simulation software called DesignBuilder (DB). For the experimental study, a shipping container with a green roof was converted into an office building. For comparison purposes, another shipping container of the same dimensions without a green roof layer was constructed and decorated in an identical way to the green roof container. Two computational models, one for green roof and other for non-green roof were developed. A 4 °C temperature difference between the green roof and non-green roof containers was observed on a typical summer day. For the green roof, the maximum variation between the simulated and measured data was found to be 5% for temperature, 7.5% for humidity and 9.4% for energy consumption. The study found that an extensive green roof on a building in the Central Queensland sub-tropical climate (Australia) can achieve energy savings of 13.65% (simulated) and 11.70% (measured) compared to a non-green roof.

Hydrological and thermal regime of a thin green roof system evaluated by physically-based model

Green roofs, as an element of the green infrastructure, contribute to the urban heat island effect mitigation and the urban drainage outflow reduction. To achieve the desired functions, it is essential to understand the role of the individual roof layers and ensure their proper design.A physically-based model was used to assess the hydrological and thermal regime of two experimental green roof test beds containing distinct soil substrates (a local Technosol and a more permeable commercial substrate “Optigreen”). The test beds together with a meteorological station were built on the building green roof. Each test bed has an effective area of one square meter and is equipped with a soil temperature sensor and an outflow gauge; one of the test beds is continuously weighed. The observed conditions were simulated using one-dimensional numerical model describing the water flow in variably saturated porous medium by Richards’ equation and the heat transport by the advection-conduction equation.The model was able to satisfactorily reproduce the measured outflow and soil temperature. The water-potential-gradient based root water uptake module effectively captured the water storage depletion between the rainfall events. The difference between the two soil substrates tested is demonstrated by the contrasting ability of the soil layers to retain water. Model representation of the thermal conditions within the green roof soils was achieved using independently evaluated thermal properties of the soils and drainage board. The model was also used to analyze the effects of the substrate depth and type of vegetation cover on the transpiration and soil water regime of the green roofs. Increasing the substrate depth causes a rise of root water uptake and induces a significant reduction of the maximal temperature. The thinner soil profiles are more sensitive to the plant species selection.

Degradation of PVC Waterproofing Membrane containing Plasticizers

Durability and repairability are one of the basic conditions for the economically efficient use of building materials. The actual lifetime of PVC waterproofing membrane is not only affected by the ageing of the materials, but also by the ageing of the joints. Thus, a significant phenomenon in the evaluation of the lifetime of roof cladding is its realisation - welding. Plasticizers are used for the production of PVC waterproofing membrane. The migration of the plasticizers and the quantity of non-combustible residues (fillers) influence the service life (durability) and the possibility of subsequent repair. Methods used to determine the quantity of non-combustible residues and quantity of plasticizers are described in the paper. Samples were taken from roofs with degrading roofing layer. Based on the results, the lifetime of the PVC waterproofing membrane was determined in dependence on the plasticizers.

Design a Reasonable Width of Coal Pillar Using a Numerical Model. A case study of Khe Cham basin, Vietnam

Problems in surrounding rock displacement, roadway deformation and complex support are the hallmarks of the long wall mining system. Such problems seriously affect the safety and efficient production of coal mines. To control the deformation of the rocks around the roadway next to the goaf, to reduce the support pressure, in Vietnamese underground mines often leave supporting coal pillars. Identification of a reasonable design for roadway supporting pillars by a numerical simulation study was conducted under the geological and technical foundation of I-10- 2 working faces at the Khe Cham coal mine, Vietnam . The characteristics of stress and pressure distribution of roof layers on coal pillars are modeled under different pillar widths. The results show a great linear increase of the vertical stress on the narrow coal pillar and as the width of the coal pillar increases, the area of the elastic core area also increases and the level of stress increase tends to be stable without any apparent uptrend. Coal pillar deformation decreases with increasing coal pillar width, but it leads to large coal loss and waste of resources. Therefore, with the current supporting solutions to increase the stability of the coal pillar, the size range of a coal pillar is determined to be 6-8 m through numerical simulation. The conclusions obtained may provide a certain reference number to choose the logical location of the furnace lines under similar geological conditions.

Evaluation significance of differences between the geotechnical parameters of the lithological rocks roof layers, above mining excavation

1. BUTRA J., KICKI J., 2003, Ewolucja technologii eksploatacji złóż rud miedzi w polskich kopalniach. Biblioteka Szkoły Eksploatacji Podziemnej nr 17, Kraków (in Polish). Google Scholar

Analysis of roof greening technology impact on rain and meltwater retention

Over the past 20 years, a large number of studies have been published on reducing storm runoff by various types of green roofs. This article analyzes the results of experimental studies presented in 39 publications on green roof runoff reduction in a climate similar to the climate of Russia: in Canada, the USA, Finland, Norway, France. An analytical review found that the ability of green roofs to retain rainfall varies from 20 to 99.5% depending on climatic conditions (duration and intensity of rains, duration of dry periods, solar radiation, temperature and humidity, wind conditions), the properties of green roof layers (moisture capacity of the substrate and a drainage layer, the substrate thickness), the type of vegetation, the geometry of a green roof (slope and orientation). Green roofs can be a useful tool for reducing urban storm water runoff. However, in order to ensure high efficiency, it is necessary to use green roof technology with other measures to reduce runoff.

Research on the control technology of heavy layer hard roof blasting

In this paper, based on the typical geological features of heavey layer hard roof, around a blasting weakening control of complete sets of technology, through the theoretical calculation and numerical simulatio, analyses the rules of the thick layer of hard roof and the characteristic of mine pressure appear; Based on the theoretical analysis, the attenuation height of vertical blasting and the circular blasting distance are determined. By weakening roof blasting scheme design, pull cut blasting with two lane ahead of deep hole blasting weakening technology, this paper introduces hole arrangement, drilling tool, design parameters control and instrument. A complete set of technical measures to reduce the control of hard roof blasting in thick layer is formed, and the rationality of the technical measures is confirmed by field observation. The relevant research results have important practical significance and reference value to the hard roof management of similar geological conditions.

Economical Aspect of Sensitive Flat Roof Renovation

The authors have been working for a long time on the development of sophisticated flat roof renovation that would allow renovation without the need of removing the existing roof layers and so will have a positive environmental impact. The solution is based on the detailed hydrothermal analysis of flat roof and using the potential of the original materials. Subsequently, new layers of the flat roof with optimal parameters for a certain case and possibly other construction modifications are designed. The aim of the development is to create a methodology to achieve equilibrium humidity by perforation of the original waterproof layer. In the paper, the authors describe the key points of this methodology. However, the paper focuses on the economic aspect that this sophisticated renovation brings. Economic evaluation is described through two methodological approaches. The authors compare the developed method with the method involving renovation of flat roofs with the need of removing the existing roof layers. The comparison takes into account the use of different materials for waterproofing and thermal insulation. In order to determine the costs, the authors used the building software to create budgets. The presented economic evaluation confirms the essence of the developed method.

Shaking table tests on the multi-dimensional seismic response of long-span grid structure with base-isolation

Seismic isolation technology is being applied in large long-span-structured public buildings more and more often worldwide. Aimed to investigate the horizontal and vertical dynamic response of long-span gird structure, the shaking table tests of 1/20 scale long-span grid structures with and without base-isolation considering horizontal two-dimensional (2D) and three-dimensional (3D) seismic excitations were conducted. The test model was designed as ordinary long-span spatial grid structure, but with lead rubber bearings. Data on the acceleration, displacement, strain, and shear force of the base-isolation model and fixed-base model were collected and compared. The dynamic responses of the structure subjected to the horizontal and vertical ground motions with different intensities were studied. The experimental results showed that compared with the fixed-base model, the horizontal period and damping ratio of the base-isolation model can be significantly improved, reducing the horizontal dynamic response of the superstructure, and the horizontal isolation effect was improved with the increase of the seismic excitation intensity. The horizontal acceleration of the roof layer for the base-isolation model was amplified in 3D excitation compared to horizontal input due to horizontal-vertical coupling. Meanwhile, significant vertical acceleration and displacement responses of long-span roof for fixed-base structure were induced by horizontal seismic excitation. Although base isolation could not provide protection against vertical excitation, vertical isolation effect under 3D input could be achieved by effectively suppressing the vertical dynamic response of grid roof induced by the horizontal seismic component.

Preparation of Polyethylene and Ethylene/Methacrylic Acid Copolymer Blend Films with Tunable Surface Properties through Manipulating Processing Parameters during Film Blowing.

Polymer films based on polyethylene (PE) and ionomer ethylene/methacrylic acid (EMAA) copolymer blend were prepared by film blowing, whose surface properties were tuned by varying processing parameters, i.e., take up ratio (TUR). Blends of PE/EMAA copolymer were firstly prepared by the melt-mixing method, before being further blown to films. The wettability of the film was investigated by measuring the contact angle/water-film encounter time, and optical properties, i.e., the haze and transmittance. The wettability was found to be enhanced with the increase of TUR. So too was the haze, while the transmittance was found to be almost independent of TUR. The XPS and AFM results directly show the increasing polar functional groups (–COO−) on the surface and roughness with increasing TUR. Further analysis of the 2D SAXS and WAXS unveiled the origin of the invariant transmittance, which resulted from the minor change of the crystallinity and the monotonic increase of the haze, with TUR resulting from the evolution of crystal orientation. In addition to other post-modification methods, the current study provides an alternative route to prepare large-scale PE films as the template for the advanced potential applications, i.e., covering in the layer of roof, the privacy of protective windows, and multitudes of packaging.

Flat roof hygrothermal performance testing and evaluation

PurposeUnderstanding the dynamic hygrothermal behavior of building elements is very important to ensure the optimal performance of buildings. The Laboratory for Quality Control in Buildings of the Basque Government tested a flat roof designed by a construction company that developed a building to be constructed using prefabricated modules. This is a five to eight floor building with ventilated façade and a flat roof covered by gravel with the possibility of changing it to a green cover. The paper aims to discuss this issue.Design/methodology/approachThe interest of this research was threefold. The first objective was to accurately test, under real dynamic weather conditions, the roof design in a PASLINK test cell to obtain the U-value and the thermal capacitance of the different roof layers, and of the roof as a whole, through the precise calibration of resistance-capacitance mathematical models of the roof. Based on the parameters and experimental information of these calibrated models, a second goal was to calibrate and validate a Wufi model of the roof.FindingsThis second calibrated model was then used to simulate the dynamic hygrothermal behavior of the roof, obtaining the roof’s hourly thermal demand per square meter for a whole year in different locations considered in the Spanish Building Code. These simulations also permitted the authors to study the risk of condensation and mold growth of the tested component under different climatic conditions.Originality/valueThe successful combination of the PASLINK method to calibrate the Wufi hygrothermal model is the main novelty of this research.

Experimental study of thermal characteristics for a novel ventilation roof with composite phase change material (VRCPCM)

A phase change material particle (PCMP) was prepared by vacuum adsorption method, with the binary eutectic mixture of myristic acid and tetradecanol as phase change material (PCM) and expanded vermiculite (EVMT) as porous adsorption materials. Then PCMPs were pressed into composite phase change plates (CPCP) for the outside layer of roof to store the heat passively. The active cooling storage was provided by the cold water in the seamless steel pipe and the iron box containing binary eutectic mixture of lauric acid and tetradecanol on the indoor side. Combined with the ventilation roof, a novel ventilation roof with composite phase change material experimental hut was constructed. The cold storage performance test was conducted under the two strategies which were regularly opened ventilation layer at certain time and timing cooling while regularly opened ventilation layer. The first strategy result showed that CPCP effectively reduced the temperature of the outer surface of the roof and the ventilation layer was turned on at night, which could effectively reduce the indoor air peak temperature. The second strategy result under the active cooling condition showed that the indoor PCM could absorb the heat of the indoor air and reduce the indoor temperature and the indoor temperature fluctuation range.

Increasing Evapotranspiration on Extensive Green Roofs by Changing Substrate Depths, Construction, and Additional Irrigation

Urban environments are characterized by dense development and paved ground with reduced evapotranspiration rates. These areas store sensible and latent heat, providing the base for typical urban heat island effects. Green roof installations are one possible strategy to reintroduce evaporative surfaces into cities. If green roofs are irrigated, they can contribute to urban water management and evapotranspiration can be enhanced. As part of two research projects, lysimeter measurements were used to determine the real evapotranspiration rates on the research roof of the University of Applied Sciences in Neubrandenburg, Germany. In this paper, we address the results from 2017, a humid and cool summer, and 2018, a century summer with the highest temperatures and dryness over a long period of time, measured in Northeast Germany. The lysimeter measurements varied between the normal green roof layer (variation of extensive green roof constructions) and a special construction with an extra retention layer and damming. The results show that the average daily evapotranspiration rates can be enhanced from 3 to 5 L/m2/day under optimized conditions. A second test on a real green roof with irrigation was used to explain the cooling effects of the surface above a café building in Berlin.

Investigating the post-mining subsidence and the long-term stability of old mining excavations: case of Cow Pasture Limestone Mine, West Midlands, UK

Assessing the long-term stability of abandoned mine workings is a challenging problem in geo-mechanical engineering. There are several factors contributing to the long-term behaviour of excavations. Creep and the gradual deterioration of rocks are, in particular, among the dominant factors affecting the long-term stability of abandoned mine workings. In this paper, the mechanism of post-mining subsidence over old room-and-pillar mine workings is investigated. A case history of post-mining subsidence over Cow Pasture abandoned limestone mine in the West Midlands of the UK is presented. The geological and geotechnical characteristics of the mining site are explained. Empirical and analytical approaches are then used to study the mechanisms of post-mining subsidence. Outcomes of the analyses show that the bearing capacity failure of the roof strata and the gradual punching of pillars into the moisture-sensitive roof layers have been the key mechanisms initiating failure and leading to the formation of post-mining subsidence in the Cow Pasture Mine.

Thermal behaviour of a green roof containing insulation cork board. An experimental characterization using a bioclimatic chamber

Green roof technology is increasingly being used to improve the energy and environmental performance of buildings. However, the description of the thermal behaviour of green roofs is very complex since it depends on several variables and relies on intricate phenomena.In this work the authors characterize a green roof system that replaces the conventional drainage and water storage polyethylene membranes with insulation cork boards (ICB). To enable the experimental characterization of this system, a double walk-in bioclimatic chamber was designed and built to recreate indoor and outdoor environmental conditions. Winter and summer environments with steady and unsteady conditions in both dry and wet states were simulated. Thermocouples and heat flux sensors were used to collect data over time from the different layers of the green roof prototypes.Measurements were first performed on a concrete slab insulated with ICB to assess the contribution of the latter to the thermal performance of the system. The effect on the heat transfer was further evaluated for systems of increasing complexity, containing first a substrate layer and then vegetation. It was noted that the substrate and vegetation layers improved the thermal insulation, and reduced heat fluxes and the thermal amplitude within the system. The vegetation layer was found to be of key importance to the overall performance of the green roof. It was also found that ICB and the substrate layers lose part of their insulation capacity when the system was wetted, although it was fully restored in the ICB layer within a few hours.

Green Roof Design: State of the Art on Technology and Materials

In order to consider green roofs as an environmentally friendly technology, the selection of efficient and sustainable components is extremely important. Previous review papers have mainly focused on the performance and advantages of green roofs. The objective of this paper is to examine the primary layers: The waterproof and anti-root membranes; the protection, filter, and drainage layers; the substrate; and the vegetation. First, the history, modern applications, benefits and classification are analyzed in order to present a well-defined state of the art of this technology. Then, the roles, requirements, characteristics, and materials are assessed for each green roof layers. This technology was compared to a conventional roof technology, Mediterranean climate conditions and their influence on green roof design were assessed, also comparing them with Tropical area and focusing on irrigation systems, examples about the commercial materials and products available in the market were provided and innovative materials coming from recycled sources were analyzed. Future research should evaluate new materials for green roof technologies, in order to enhance their performance and increase their sustainability. The information provided in this review paper will be useful to develop Mediterranean green roof guidelines for selecting suitable components and materials during the design and installation phases.

Study on the mechanism of roof collapse and leakage of horizontal cavern in thinly bedded salt rocks

In the thinly bedded salt formations, due to the limited thickness of the salt strata along with the fast upward dissolution, the collapse of the non-salt roof of the cavern often occurs, leading to the leakage of brine and instability of the cavern as well as other undesirable geological consequences. To investigate the gypsum-salt interbedded roof collapse, the failure mechanism and the control methods of Dainan siltstone, which is the indirect roof of the horizontal salt caverns in Zhaoji Salt Mine, were thoroughly investigated. Through the drilled cores from this mine, a series of contrast tests such as SEM, EDS, XRD, soaking, and nuclear magnetic properties were carried out to study the physical properties of the salt layer and non-salt layer of the cavern roof and to determine the cavern roof collapse and leakage mechanism. Using the Comsol software, the model of a horizontal cavern roof leakage was established, and the leakage range and leakage of brine at different time were analyzed, as well as the safety problems caused by it. Finally, some suggestions have been provided for the leakage control of the cavern roof in bedded salt cavern.

LES simulation of flow field and pollutant dispersion in a street canyon under time-varying inflows with TimeVarying-SIMPLE approach

Field observation data have shown that the actual wind speed and direction in an urban built environment always vary with time. Realizing the flow field simulation under time-varying inflows can have a great significance in fully understanding the airflow and the transportation of air pollutants in the atmospheric boundary layer. A new scheme based on the standard SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm has been implemented in OpenFOAM, named as TimeVarying-SIMPLE approach, to simulate the time-series airflow field under time-varying inflows in this study. The accuracy of TimeVarying-SIMPLE approach compared with PISO (Pressure-Implicit with Splitting of Operators) algorithm and PIMPLE (merged PISO-SIMPLE) algorithm was validated by solving the fully developed laminar flow in a straight pipe under sinusoidally varying inflow. The wind field and pollutant dispersion in an ideal street canyon with an aspect ratio of 1 under time-varying inflows were calculated using the TimeVarying-SIMPLE approach. The flows show an obvious flapping of the shear layer near the roof layer and the expansion or shrinkage of the main vortex under time-varying inflows, resulting in a significant increase of the removal efficiency of pollutants inside the street canyon compared to that under steady inflow. The average time of actual high-frequency wind speed data is critical to produce the time-varying inflows for the boundary conditions of numerical simulations, which could produce different simulated removal efficiency of pollutants inside the street canyon. The appropriate average time should be estimated by the pre-multiplied power spectrum of the measured high-frequency wind-speed data.

Lowering Emissivity of Concrete Roof Tile’s Underside Cuts Down Heat Entry to the Building

Buildings in Southern China widely use a double-skin roof to reduce heat entry through the roof to the building interior during summertime. Concrete roof tiles are preferably installed as the outmost layer of the double-skin roof due to their resistance to hail and wind damages and their attractive price. However, after construction, the tile’s top tends to be darkened by dust deposit and algae growth, increasing the heat entry through the roof to the building. Here, we show that this heat entry can be curtailed by lowering the emissivity at the tile’s underside. Temperatures and heat fluxes at different elevations of a double-skin roof with concrete tiles as the outmost layer of the roof are monitored. The underside of each concrete tile is coated with a specific paint to get a unique emissivity. Observations reveal that lowering the emissivity of concrete roof tiles could cut down the summer heat gain of buildings in tropical regions.

The informativeness of roof tremor hazard analysis based on seismic measurements and analytical modelling

Rock bursts are a common hazard in Polish hard-coal mines. Their magnitude depends on the state of stress in the mining area, and on underground mining-induced seismicity. Both long-term and ongoing as-sessments of the capacity of the rock mass to generate tremors are based on geological and mining surveys, rock property measurements (in laborato-ries and in-situ) and observations involving signs of rock mass pressure, supported by available concepts applicable to geomechanical and geophys-ical measurements. These include seismic measurements, including profil-ing, scanning, passive/active geotomography and analytical techniques. This paper presents a comparative analysis involving exemplary results provided by both seismic and analytical methods for a selected panel in one of Upper Silesian Coal Basin (USCB) mines. For the purposes of our seismic measurements, we employed seismic tomography for the ge-otomographic reconstruction of velocity fields. Subsequently, we com-pared the results with the results of analytical modelling of rock stresses that relied on classical engineering solutions applicable to problems of me-chanics of deformable bodies. The tremor hazard analysis was based on observations of changes in P-wave velocity distributions in the coal seam environment relative to the evolution of the vertical stress concentration factor at the level of a potentially seismogenic roof layer.