Roof Pitch Research Articles

Effects of roof pitch gradient and material to harvested rainwater quality

Rainwater harvesting has untapped potential in domestic usage due to the lack of awareness and design guidelines to building sustainable roofs. Studies suggest that combinations of different roof pitch gradient and materials will affect the runoff quality. The level of contamination and contents found in the harvested rainwater will require different ways for water treatments prior to usage. The objective of this research is to identify design criteria of a building roof affecting the roof runoff quality in Kuala Lumpur. Quantitative analysis is done based on the rainwater collected from case studies with combinations of different roof pitch and materials to identify the contents and level of contamination in each of the collected sample. The result observed the best runoff quality from clay tile roof of 45°, metal roof of 15° and polycarbonate roof of 15°; whilst reinforced concrete (RC) flat roofs harvested the most contaminated runoffs. The study shows that all roof runoff quality is not up to potable standard though can be used for indoor non-potable use with minimal treatment.

Performance of thin-film BIPV as double sloped pitched roof in buildings of Malaysia

ABSTRACTSolar energy in built environments became more popular in the recent years emerging as building integrated photovoltaics (90° façade and 0° roof BIPV). However, in most cases, residential buildings have varying roof pitches instead of 0° roof. In this context, it is significant to assess the energy output and performance of double-sloped pitched roof thin-film BIPV at different angles and orientation. Results show that the performance of the BIPV inclined at 15° and east orientation is better among the other orientation and angles.

Study on localised wind pressure development in gable roof buildings having different roof pitches with experiments, RANS and LES simulation models

In this study, the influence of different roof pitches on the mean pressure distributions around isolated buildings subject to different wind directions were investigated with wind tunnel tests, 3D steady Reynolds-averaged Navier-Stokes (RANS) simulation and large eddy simulation (LES). Wind tunnel experiments were conducted to obtain mean pressure distributions around buildings having three commonly used roof pitches, namely, 1:5, 2:5 and 3:5. The critical high suction areas created by conical vortices were identified, and the influence of roof pitch on these critical areas with high localised pressures was investigated under various wind directions. In addition, computational fluid dynamics (CFD) analysis was performed, and the performance of RANS and LES were evaluated and compared with the results measured from the wind tunnel tests by considering both the accuracy of results and computational cost. The assessment on RANS and LES was used to determine the best guidelines for the flow problems involved in this study.Results from the RANS show good agreement with the experimental results on pressure distribution when the building is subject to perpendicular wind directions. However, a significant improvement was found using LES over RANS in the prediction of near-building flow field and localised pressure under oblique wind directions but with an increased computational cost by a factor of more than 80. Furthermore, the high suction pressures are observed to be more critical on buildings with a lower roof pitch under both perpendicular and oblique wind directions. This indicates that a low roof pitch should be applied with caution especially in windstorm-prone areas.

Enhancement of CFD validation exercise along the roof profile of a low-rise building

The aim of this study is to enhance the validation of CFD exercise along the roof profile of a low-rise building. An isolated gabled-roof house having 26.6° roof pitch was simulated to obtain the pressure coefficient around the house. Validation of CFD analysis with experimental data requires many input parameters. This study performed CFD simulation based on the data from a previous study. Where the input parameters were not clearly stated, new input parameters were established from the open literatures. The numerical simulations were performed in FLUENT 14.0 by applying the Computational Fluid Dynamics (CFD) approach based on steady RANS equation together with RNG k-ϵ model. Hence, the result from CFD was analysed by using quantitative test (statistical analysis) and compared with CFD results from the previous study. The statistical analysis results from ANOVA test and error measure showed that the CFD results from the current study produced good agreement and exhibited the closest error compared to the previous study. All the input data used in this study can be extended to other types of CFD simulation involving wind flow over an isolated single storey house.

Monitoring of a Cold Roof Thatched with Reed (Phragmites australis) Using Wooden Substitute Sensors for Moisture Content Measurements

AbstractReed (Phragmites australis(Cav.) Trin. ex Steud.) is a traditional building material in many parts of the world and provides service lives of more than 50 years when used for thatching. However, during the last decades a significant number of thatched roofs showed premature failure due to decay. Potential reasons for this are manifold but not clearly identified, yet. This monitoring project aimed therefore on investigating the moisture and temperature conditions within a thatched roof structure showing severe degradation after only seven years in service to obtain more information about the decay risk of reed and its potential causes. Highest moisture loads were found on the outermost layers of the North-faced roof, which also showed superficial growth of algae, lichens, and mosses. However, it stayed unclear if increased moisture content (MC)was the reason for or the consequence of decay. An increasedMCwas also found where the roof pitch turned from steep to flat. The use of so-called substitute sensors made from preservative treated wood turned out as a useful method to determine equilibrium moisture contents as well as time of wetness in reed structures and might be applied also for further field testing and monitoring with reed, straw, or other organic fibrous materials.

Experimental study of wind loads on gable roofs of low-rise buildings with overhangs

Gable roofs with overhangs (eaves) are the common constructions of low-rise buildings on the southeastern coast of China, and they were vulnerable to typhoons from experience. The wind pressure distributions on gable roofs of low-rise buildings are investigated by a series of wind tunnel tests which consist of 99 test cases with various roof pitches, height-depth ratios and width-depth ratios. The block pressure coefficients and worst negative (block) pressure coefficients on different roof regions of low-rise buildings are proposed for the main structure and building envelope, respectively. The effects of roof pitch, height-depth ratio, and width-depth ratio on the pressure coefficients of each region are analyzed in detail. In addition, the pressure coefficients on the roofs for the main structure and building envelope are fitted according to roof pitch, height-depth ratio and width-depth ratio of the low-rise building. Meanwhile, the rationality of the fitting formulas is verified by comparing the fitting results with the codes of different countries. Lastly, the block pressure coefficients and worst negative pressure coefficients are recommended to guide the design of low-rise buildings in typhoon area and act as references for the future’s modification of wind load codes.

Risk Analysis of Three-storey Reinforced Concrete Moment-resisting Frame Structures Using Performance-based Wind Engineering

This paper discusses the application of concepts of performance-based wind engineering used to determine the effects of changing building design elements to the performance of a structure against severe wind hazards in the Greater Metro Manila Area, Philippines. Only three-storey reinforced concrete moment-resisting frame structures were subject to analysis through computational fluid dynamics. Before assessing the performance of structures, severe wind hazards for the study area was characterized by collecting wind speed data from over 50 years and fitting the data using the Gumbel distribution. The building stock was developed by varying roof pitch and floor aspect ratio values in certain set increments. Roof pitches observed were 15, 30, and 45 along with structures with floor aspect ratios of 1:1, 1:2, and 1:3. The damage to roof and windows, as well as the damage index which gives the ratio of the repair cost to the replacement cost of a building, were identified. Damage for each model was classified according to the Hazard-US Damage State Matrix in order to generate a damage probability matrix. From this damage probability matrix, the probability of exceedance of each damage state was compute by taking the cumulative probabilities. Data points for each damage state were then fitted with a lognormal function. Vulnerability curves were developed by multiplying the probability of exceedance of each damage state to cost percentages adopted from the UPD-ICE Report [2]. Damage indices were computed per wind speed by summing the total damage for damage states. Wind speed versus risk density curves were generated by multiplying values for each data point in the vulnerability curves to the probability density function of the hazard. Risk curves were then obtained by plotting wind speeds against values of damage indices that correspond to said wind speeds. One key observation is that damage percentage increased as roof pitch also increased, having as much as around a 15% difference between structures with roof pitches of 15 and 45. Slender structures whose windward sides were also the long sides had the most damage. For all structures, a top-to-bottom progressive damage trend was observed.

Wind Directional Effect on a Single Storey House Using Educational Wind Tunnel

Wind tunnel testing of single-storey isolated building with 1: 100 scale down model was carried out in an open circuit wind tunnel without roughness elements facilities. The gable roof building model with 30˚ roof pitch was studied for wind directions of 0˚, 30˚, 45˚, 60˚ and 90˚. Pressure measurements were performed on all the walls and the roof (Zone 1, 2, 3, 4 and 5) of the building model with wind speed of 12 m/s. The results showed that the high suctions were generally induced by the 90˚ wind direction for Zone 1 and 60˚ and 90˚ wind directions for Zone 2. Mostly, high suction was also observed in case of 45˚ and 60˚ wind direction in Zone 3. In zone 4 and zone 5, high suction was generally induced by the 0˚ wind direction.

Growing fresh fruits and vegetables in an urban landscape: A geospatial assessment of ground level and rooftop urban agriculture potential in Boston, USA

Urban parcels can potentially be leveraged for developing a local urban food system by growing high yield food crops. Here, a remote sensing and GIS-based modeling framework was developed to locate and quantify available area for urban farming, including both rooftop and ground level areas in the city of Boston, MA, USA. Geoprocessing and spatial analysis tools were used to process geographic data layers for zoning, ownership, slope, soil quality, and adequate light availability. Surface slope (roof pitch) was determined for all buildings in the city through the creation of a digital surface map from remotely sensed LiDAR data. Potential parcels from ground level public and private vacant lots and underutilized residential and commercial areas were mapped using publicly available datasets. Approximately 922ha of rooftop and 1,250ha of ground level parcels have been identified, representing 7.4% and 10% of the total land area in Boston, respectively. Finally, food yield values for common urban agricultural crops were used to estimate the city’s food production potential from the identified parcels. Despite Boston’s density, the mapped areas have potential to produce enough fresh fruits and vegetables for Boston’s population, while providing both environmental and economic co-benefits. The study outcome was compared with mapping and inventory results from other North American cities.

Wind Loads for Stability Design of Large Multi-Span Duo-Pitch Greenhouses

An atmospheric boundary layer wind tunnel study was performed to determine the overall horizontal wind load on multi-span duo-pitch greenhouses. The results of this study are intended for the stability design of inflexible Gladding system greenhouses (designated as Class A in EN 13031-1) with roof pitch angles of 23-24' and ridge heights of 7.5-8 m. Both static force and fluctuating pressure measurements were performed to determine the overall horizontal wind force. The results obtained with the static force measurements show that the overall horizontal wind force increases linearly with increasing number of spans. The overall horizontal wind load determined with the mean pressure coefficients derived from the fluctuating pressure measurements was found to be in good agreement with the static force measurements. An investigation into the correlation of the roof pressures showed that these pressures are relatively little correlated. The overall horizontal force on the roof of multi-span buildings reduces significantly because of this lack of correlation. Accounting for the lack of correlation between the roof pressures on a 30span model resulted in a 65% reduction of the peak horizontal wind force on the roof. A comparison was made of the overall horizontal wind forces determined in the current study and calculated with European codes for wind load assessment on greenhouses. EN 13031-1 provides non-conservative outcomes for the overall horizontal wind force on the investigated duo-pitch greenhouse type with more than 30 spans. On the other hand, EN 1991-1-4 is increasingly conservative with larger number of spans.

On the effect of gable roof on natural ventilation in two-dimensional urban canyons

Flow regimes occurring in urban canyons are strongly influenced by the geometrical shape of the buildings; however, fluid dynamic investigations are typically carried out using parallelepiped obstacles. The present study is focused on assessing the effect of gable roofs on the flow regimes characterizing urban canyons (skimming flow, wake interference, isolated roughness) and the implications in terms of integral parameters (air exchange rate and friction factor), which are useful in practical applications. Numerical simulations are performed by means of RANS modeling of idealized two dimensional urban canyons between series of identical gable roof buildings with pitch ranging from 0° up to 40°, and wind direction perpendicular to the canyon axis. Simulations performed for different canyon aspect ratios show the key role played by the roof pitch in enhancing turbulence and in increasing ventilation, in particular for narrow canyons. Furthermore, turbulence-driven ventilation is observed to be related to the square root of the friction coefficient by a single linear relation, despite of the roof pitch. These results may have an impact on design and planning strategies aimed at enhancing natural ventilation and promoting efficient pollutant and heat dispersion in urban areas.

Post Windstorm Evaluation of Critical Aspects Causing Damage to Rural Houses in the Northern Region of Peninsular Malaysia

Rural houses are susceptible to roof blown off and severe damage during a windstorm event due to the lack of engineering considerations. The aim of this paper is to conduct a post windstorm evaluation on the damaged rural houses located in the northern region of Peninsula Malaysia. Several activities were involved during the post windstorm survey including site visualization, site measurement and interview. Critical aspects including types of damages, types of houses, gap height, overhang length, roof geometry, roof pitch, roof cladding and terrain category were analysed using a simple bar chart. It is anticipated that the presence of kitchen house influences the overall stability of the rural houses due to the formation of gap height.

A Computation of U-Factor for an Entire Vented Attic Assembly using a 2D Model

The overall U-factor values for an attic assembly are usually computed with the ANSI/ASHRAE/IES based R-value (thermal resistance) conversion. In the ANSI/ASHRAE/IES Standard 90.1 (2010), the effects of attic air resistance, roof pitch and attic width are not taken into account while calculating the U-Factor values. In addition, the R-value is estimated using a one dimensional thermal resistance model. In ventilated attics, where the insulation near the roof sheathing is tapered, it is difficult to find the correct R-value of the attic system as the heat transfer becomes two dimensional. In this paper, a 2-dimensional CFD model is developed for various insulation R-values and insulation taper angles near roof decks. COMSOL Multiphysics 4.4 is used to model and analyse the attic structure. Results show that a discrepancy in overall U-factor for entire attic assembly between the developed model and the existing standard estimation. These results are pronounced for lower slope roofs with high insulation thickness.

Wind flow over the low-rise building models with gabled roofs having different pitch angles

In this study, the turbulent flow fields on the low-rise building models with gabled roofs having different pitch angles immersed in atmospheric boundary layer have been investigated experimentally and numerically. The models of the Belgian Building Research Institute (BBRI) test building with a scale of 1:100 were studied with 15°, 30° and 45° roof pitches for the wind direction of 90°. Flow visualization, measurements of velocity and surface pressure around the models placed in wind tunnel were made. 3D solutions of the flow fields were obtained with two different turbulence models. The mean velocity and turbulence kinetic energy profiles are influenced by the roof pitch. Recirculation regions occur on the leeward part of roofs and at the behind of the models due to flow separation. These regions are much stronger and spread up to the roof ridge with increasing roof pitch. Largest values of turbulence kinetic energy for entire flow field occur at height of the roof level and they prove the presence of the mixing layer between the free stream flow and reverse flow region. It is seen from the surface mean pressure distributions that the 15° roof pitch causes more critical suction on the roofs than those of the 30° and 45° roof pitches. The numerical results shows that Realizable k-ε turbulence model exhibit better agreement at the prediction mean velocity and turbulence kinetic energy while Standard k-ω turbulence models exhibit better agreement at the prediction of mean pressures coefficients.

Roof pitch and exposure and different roofing materials in reduced models of animal production facilities in the fall and winter

AbstractThe objective was to verify the influence of roof pitch, exposure and roofing material on the internal temperature of reduced models of animal production facilities. For the development of the research, 48 reduced models with dimensions 1.00 × 1.00 × 0.50m were used. The roof was shed-type, and models faced the North or South directions, with 24 models for each side of exposure. Ceramic, galvanized-steel and fibro tiles were used to build the roofs. Pitches varied between 20; 30; 40 and 50% for the ceramic tile and 10; 30; 40 and 50% for the other two. Inside the model, temperature readings were performed at every hour, for 12 months. The results were evaluated in a general linear model in a nested 3 × 4 × 2 factorial arrangement. As the roof pitch increased, the internal temperature within the model dropped, so utilizing sharper pitches (50%) for ceramic and fibro roofs with a larger area facing the South can provide lower temperatures within the animal production facilities. In regions where the cold is more stressful than the heat, having animal production facilities with larger roof exposure to the North may minimize the losses caused by cold stress.

The effect of building integrated photovoltaic system (Bipvs) on indoor air temperatures and humidity (Iath) in the tropical region of Cameroon

The building sector accounts for around 40-50 % of the energy consumed in developing countries and contribute over 30 % of CO2 emissions. In Cameroon, the electricity access is less than 5 % in rural areas against 50 % in urban areas. All sectors combined the Cameroonian final energy consumption amounts to approximately 5235 kilo-tonnes of oil equivalent (Ktoe) and 73 % of this energy are assigned for residential use. This energy can be considerably reduced with the development of low energy buildings using Building Integrated Photovoltaic (BIPV), since it has been proven an effective solution to achieve significant energy savings and conservation. However, photovoltaic (PV) panels produce a substantial amount of heat, while generating power. Consequently, BIPV’s concept, where the photovoltaic (PV) panel is integrated on the building envelops has significant influence on the amount of heat transfer through the building fabrics, and could affect the indoor air temperatures and the comfort of the occupants, since, it changes the thermal resistance of the building envelops. In this paper, the effect of the BIPV on the indoor air temperatures and humidity (IATH) of a multiple storey buildings under the tropical climatic conditions of Yaounde, Cameroon has been modelled and analysed. Two cases of BIPV made of 290 m2 area of PV have been considered, i) roof integrated and ii) facade integrated. In addition, building orientation, roof pitch and the building materials are also been explored and optimised to provide the best combination. It has been observed that for both cases, BIPV increases the building’s indoor air temperature by about 4 °C, when compare to a building of the same size without PV integrated.

Volcanic ashfall accumulation and loading on gutters and pitched roofs from laboratory empirical experiments: Implications for risk assessment

Volcanic ash load is dependent on the migration and accumulation of ash on roofing surfaces and guttering, of which limited research has been conducted. This study investigates this knowledge gap through the empirical experimental testing of volcanic ash on variably pitched metal sheet roofs with modern PVC gutter systems, highlighting the relative importance of accumulation, migration, remobilization, saturation, and subsequent load.A testing rig delivered ash onto variably pitched roofs (pitches 15°, 25°, 30°, 35°, and 45°) with two 45° tests involving a wet surface with subsequent ashfall, and the second of ashfall with periods of wetting, followed by wetting until failure. In testing, dry ash on a dry roof accumulates at pitches up to 35°, above this pitch the percentage of ash accumulating reduces with greater percentages infilling guttering and or lost to the ground. With the introduction of a wet roof surface at 45° pitch, adherence of dry ash greatly increases, increasing accumulated ash thickness as compared to dry tests from 8% to 38%. For testing involving periods of wetting at 45° roof pitch, accumulation percentages further increased to 50%. Ash migrating from the roof surface filled guttering more rapidly at greater pitches, which once full resulted in further migrating ash to spill over the front or back gutter lips. Collapse of guttering did not occur during testing, but deformation and bracket detachment did occur at loads >1kPa.This study provides data on load calculations on roofing and PVC guttering through the quantification and utilization of relationships between ash fate, pitch, and the influence of water, in the development of two scenarios for both roof and gutter. These two scenarios then enable the estimation of ash accumulation and thus the load and collapse thresholds for roof and gutter at different roof pitch, which could be adopted for volcanic risk modeling or risk management.

Performance analysis of photovoltaic plants installed in dairy cattle farms

Electric production from renewable resources, such as solar photovoltaic (PV), is playing an increasingly essential role in the agricultural industry because of the progressive increase in the energy price from fossil fuels and the simultaneous decrease in the income deriving from farming activities. A central issue in the sustainable diffusion of PV technologies is represented by the actual energy efficiency of a PV system. For these reasons, a performance analysis has been carried out in order to assess the potentials offered by different PV plants within a defined geographical context with the aim of investigating the impact of each component has on the PV generator global efficiency and defining the main technical parameters that allow to maximise the annual specific electric energy yield of an architectonically integrated plant, installed in a dairy house, compared to a ground-mounted plant. The annual performances of three grid connected PV plants installed in the same dairy cattle farm have been analysed: two are architectonically integrated plants - <em>i.e.</em>, a rooftop unidirectional and a multi-field systems (both 99 kW<sub>p</sub>) - and the other is a ground-mounted plant (480 kW<sub>p</sub>). Furthermore, the electrical performances, estimated by the photovoltaic geographical information system (PVGIS), developed by the EU Joint Research Centre, and by an analytical estimation procedure (AEP), developed on the basis of a meteo-climatic database related to the records of the nearest weather station and integrated by the components’ technical specifications, have been compared with the actual yields. The best annual performance has been given by the ground-mounted PV system, with an actual increase of 26% and in the range of 6÷12% according to different estimations, compared to the integrated systems, which were globally less efficient (average total loss of 26÷27% compared to 24% of the ground-mounted system). The AEP and PVGIS software estimates showed a good level of reliability for mean deviations between the annual actual and estimated electrical power yields have been equal to 11.5% for each PV system given the actual irradiation’ s uncertainty during the examined year. The main technical parameters, crucial to maximise the energy yield from a ground-mounted PV system to an integrated one, have been identified in the Tilt and Azimuth angles. Indeed, once a variance of 3÷4% in the global efficiency has been confirmed when the type of PV system is changed, in the case of the unidirectional integrated PV plant, the high roof pitch and the almost South orientation guarantee a solar energy increase up to 18% higher than that obtainable on the horizontal plane and similar to the increase estimated for the ground-mounted generator (+20%). Hence, integrated PV systems, besides reaching the same levels of energy efficiency as those ground-mounted, are also more <em>sustainable</em> than the latter. This is true providing that there are both a suitable orientation and an accurate design, especially to prevent the PV panels’ warming during summer, on an already available surface that is, however, functional to the roof’s architecture.

Practical Analysis for Horizontal Diaphragm Design of Wood-Frame Single-Family Dwellings

AbstractSeismic design of wood-frame single-family dwellings’ (WFSFD) lateral force–resisting systems requires determination of the stiffness of horizontal diaphragms and shearwalls. During design, sizes and locations of shearwall openings are often changed, altering shearwall stiffness and loads and requiring a significant redesign effort. Rigid and tributary area method analyses are examined for different geometries of L-shaped WFSFD and include stiffness reductions for roof geometry and pitch. These methods are applied to historic earthquake damage reports and compared using rigid, semirigid, or flexible horizontal diaphragm analyses useful in design practice. Most WFSFD should be designed using an envelope method because they contain a mix of horizontal diaphragm types owing to the effects of roof pitch and geometry on diaphragm stiffness. Cases occur where determination of semirigid or flexible diaphragm behavior is difficult because the analysis results are contradictory or unclear. This suggests th...

Measurement of the Influence of Roof Pitch to Increasing Wind Power Density

Abstract The wind flows on the rooftop house in Semarang, Indonesia past were examined in a Computational Fluid Dynamics (CFD) analysis and indicate best performance for wind energy power density. The rooftop pitches of house can have huge impact on increasing wind power density. This paper deals with the study to increase wind power density of micro-wind turbine located on the rooftop house by design the roof pitch. CFD was performed to evaluate the performance of wind flow around the roof pitch of housing at different angle (20 o , 30 o , 40 o and 50 o ) based on wind climate data analysis. The results showed that a pitched roof of 30 o has the best wind potential density than another for same base house model height.