Roof Drainage Systems Research Articles

Plumbing defects in residential buildings: analysis of anomalies and their causes

PurposeMost residential building owners often report problems associated with the plumbing systems. If identified at the early stages, plumbing-related defects can be easily repaired. However, if unnoticed for a long period of time, they could lead to major damages and incur a significant cost to repair. Despite the problems, studies investigating plumbing anomalies and their root causes in residential buildings are limited. This study aims to explore plumbing defects and their potential causes, diagnosis methods and repair techniques in residential buildings.Design/methodology/approachThis research used data collected through an extensive survey of both academic and grey literature. Through the content analysis, plumbing defects and the associated causes have been identified and presented in tabular format.FindingsThe study investigated the anomalies and causes in the residential plumbing system under five key sub-systems: water supply system; sanitary plumbing system; roof drainage system; heating, ventilation, air conditioning and gas system; and swimming pool. Accordingly, some of the identified plumbing defects include leakages, corrosion, water penetration, slow drainage and cracks. Damaged pipes, faulty equipment and installations are some of the common causes of the anomalies. Visual inspection, hydrostatic pressure test, thermography, high-tech pipe cameras, infrared cameras, leak noise correlators and leak loggers are techniques used for diagnosing anomalies. Reactive, preventive, predictive and reliability-centred maintenance strategies are identified to control or prevent anomalies.Originality/valueThe findings of this research can be used as a useful tool or guideline for contractors, plumbers, facilities managers and building surveyors to identify and rectify plumbing system-related defects in residential buildings.

Analysis of Siphonic Roof Drainage Systems with EPANET

Analysis and design of siphonic roof drainage systems are usually performed with specific software developed by the system’s manufacturers. An experimental study was carried out to verify if a general software for the analysis of hydraulic pressurized pipe networks can be used to analyze a siphonic roof drainage system. A test model was built and tests were conducted to compare the prototype results with simulation runs in EPANET. A new EPANET data model was developed to overcome software limitations for the siphonic drainage systems analysis. Considering the results, less than 5% of average error was observed between the measures in the real test model and the simulation results, which can be attributed to measurement error. To validate the EPANET data model, it was compared with a specific software that analyzes siphonic roof drainage systems. It can be concluded that EPANET is a software that can be used to analyze and, therefore, to design, siphonic roof drainage systems in buildings.

The Țigani Community Adaptability to Changes in Rural Romania and the COVID-19 Impact.

Romanian rural villages are struggling to survive present times when youngsters leave for a better life in the city while elders work the land like a hundred years ago. Our paper integrates human environments research with public health preparedness, presenting the Țigani (Gypsy/Roma) ethnic group from rural Romania as an example to the world. The future security of mankind will require a new understanding of the human place in its environment. That will lead to a new society, not the most powerful or intelligent, but the one that is more adaptable to changes, with sensitive and interconnected community members. Therefore, the Țigani ethnic group that fought for its rights and flourished despite unfavorable odds, including the recent COVID-19 pandemic, represents the best example for a new world that prioritizes humans, promotes health and wellbeing, facilitating innovation and transformative networks environmental integration. This research attempts to quantify the Țigani′s unique attributes that helped their communities survive and made them more adaptive to change. Always marginalized, they identified the other ethnic groups’ weaknesses to penetrate the villages and learned to use the smartphone apps to communicate, for their trades, coppersmith, metal roof tiles and drainage systems. Our research was based on Geographical Information System, Microsoft Power Bi analytics data visualization tools and statistical analysis with SPSS V20 to demonstrate what enables their flourishing and what resistance they face locally. We argue that the Țigani′s intense social cooperation, strong sense of family, community and mutual assistance helped them to fight COVID-19, generating their significant adaptability to the societal changes and their power to keep intact their cultural identity. The results show how the constant growing Țigani population changed and may change Romania′s rural environments in the future.

Evaluation of Vulnerability to Heavy Precipitation of the Roofs of Historic Chilean Buildings with Wooden Structure. A Methodology to Apply at an Early Stage

Deck areas prone to leaking rainwater can be identified at an early stage, even before the filtration process begins to occur. The identification of the factors that determine the degree of roof vulnerability to rainfall and their rainwater drainage system and the elaboration of a diagnostic procedure to be applied is fundamental, above all, for the preventive maintenance of historic buildings. In the absence of Chilean regulations on the sizing of the roof rainwater drainage system, the European standard BS EN 12056-3, the Manual for the Design of Roof Drainage Systems, the Chilean road study procedure manuals and other documents were reviewed, and the principles, concepts, dimensioning parameters, constructive recommendations, etc., were transformed into graphically represented processes to facilitate the evaluation of the safety and vulnerability of the various constructive elements to the filtration of rainwater. The factors that determine the degree of vulnerability of the roof to the filtration of rainwater are given by its conformation, its materiality, its dimensioning and its environment, primarily affecting elements such as the roof, gutters and outlets. The result that the evaluator can expect from the proposed methodology is the identification of the aspects that make both the roof and the rainwater drainage system vulnerable, distributed in space, providing him or her with the basis for designing an intervention plan and preventive actions, and this practice should be implemented for sustainable heritage conservation.

Sensitivity of Australian roof drainage structures to design rainfall variability and climatic change

The main design determinant for small catchment hydraulic structures is rainfall intensity. Localised relationships between rainfall intensity, frequency and duration (IFD) are used to design each structure to a specified level of performance. However, limitations in rainfall observations introduce uncertainty in IFD values. Further, this uncertainty is compounded by changes in climatic conditions via anthropogenic forcing. Whether this is a cause for concern depends on the structure's sensitivity to deviations away from design rainfall values. Here, we investigate the ability of roof drainage systems to accommodate deviations in design rainfall. We assess the sensitivity of box gutter overflow designs across Australia to spatial variability in IFD values, and projections of IFD values due to climatic change. Different overflow designs were found to have markedly variable responses to rainfall intensity increases, from 13% to 406% before failure. Potential increases in rainfall intensity from spatial variability uncertainty varied from 2 to 54%. While rainfall projections for the 2090 decade ranged from −15 to +59%. Rainfall intensity increases as high as 259% were noted when both sources of uncertainty were combined for a temperature rise scenario of 5 °C. At the majority of locations coupled increases in rainfall intensity were primarily driven by existing rather than future uncertainties for a 2 °C temperature rise scenario. Considering design rainfall uncertainties in terms of design sensitivity shows that adapting to present and future uncertainties can come at no additional cost for some design options while other options need to be altered to reduce the risk of failure.

Analysis of load bearing structure of selected hall buildings

In this paper the issues associated with correct design of hall buildings has been presented. Large span roof structures require a particularly careful approach to design issues. In this paper examples of two building hall were presented. In the first example, the construction disaster occurred, while in the second of presented buildings due to the changes introduced while construction has been protected against such disaster. The first of the analyzed cause concerns storage hall, whose roof structure has been destroyed due to heavy rainfall. The main cause of this disaster was the malfunction of vacuum roof drainage system compounded by a number of design errors. Mentioned errors were not eliminated, during construction, despite the additional investor supervision, which was independent of parties involved in a construction process. The second case concerns the structure of a sports hall, which was built next to the existing school. Under construction of the hall building, the contractor and the supervision inspector, in conjunction with the designer, introduced a number of modifications of the structure to prevent the disaster. These modifications were a direct result of errors at the design stage, which were eliminated under the construction works. Based on analyzed cases, the scope of diagnostics, which should be performed during the operation of hall buildings with large roof areas, was determined.

Comparing empirical water depth observations of a box gutter roof drainage system to three different international design guidelines

Effective roof drainage is necessary to protect buildings and their contents from rainfall damage. Regulatory documents exist to ensure that a building's roof drainage system is adequate for the anticipated rainfall events experienced during the life of the building. Empirical observations that inform international design guidelines are largely attributable to a small number of investigative studies with a limited range of roof drainage system configurations and flow conditions. This paper compares the observed hydraulic performance of a 600mm wide, rectangular box gutter case study model under various flowrates to values predicted in the Australian, US and European standards. The study measured the depth of water at various locations in the box gutter over a range of flowrates from 3L/s to 20L/s to determine whether the gutter depths recommended by the various design guidelines were adequate. Four different gutter slopes (1:200; 1:150; 1:100; and 1:40) were tested in the study. The results of the study indicated that the depth of flow in the box gutter was highly dependent on the inflow rate and the gutter slope. The results showed that the observed gutter water levels may or may not be considered adequate and safe, depending on the individual guideline applied. As regulatory documents aim to provide effective guidance, a deficit of box gutter depth is concerning while a surplus represents wasted resources. The findings of this study demonstrate some of the challenges faced by designers of roof drainage systems and hydraulic engineers.

Non-stationary behavior of roof drainage systems

This paper reports the non-stationary behavior of a roof drainage during experimental measurement in the climate simulator. Many buildings use a fully or partially flat roof where it is necessary to use the roof drainage. Thermal behavior of roof drainage is very important from the point of view of heat transfer and potential condensation. The placement of a roof drain slightly deteriorates thermal transmittance of the roof. This experiment evaluates roof drains in the specific climate simulator where thermal conditions were dynamically controlled in the specific temperature range. The measurement was performed for two types of roof drains. The first drainage is a simple single-shell and the second is double-shell drainage. The results show the effect on the thermal transmittance of the roof section and also the minimal effect of condensation on the non-insulation part of the drainage. Both roof drains showed minimal deterioration of thermal transmittance of the roof construction.

CHARACTERISTIC OF SIPHONIC ROOF DRAINAGE SYSTEM – PRINCIPLES AND DESIGN CONDITIONS

Amount and intensity of rainfalls are increasingly changing by clime changing and increasing of temperature variations. There is increase of torrential rains, which extremely burden the construction by the huge volume of rainwater and thus effect on whole building construction. It is necessary safely lead away this amount of rainfalls to remain the building construction undamaged. The method of roof drainage mostly depends on the roof construction. Flat roofs are more sensitive to torrential rains, thus there is very important to make proper design of drainage system and location of roof runoffs. There is no Standard for dimensioning the Siphonic roof drainage system in Slovakia. In this article is shown general procedure of design the siphonic roof drainage system, based on rules contained in the German technical regulation VDI 3806 - Dachentwässerung with Druckströmung.

Alternative low-cost overflows for siphonic roof drainage systems: Proof of concept

This paper describes an experimental investigation of alternative overflow systems for roof structures that are drained siphonically. Many buildings that have siphonic roof drainage systems currently incorporate a separate secondary overflow system, which is quite often also siphonic. An alternative low-cost technique that is explored in this study is to connect each overflow outlet to a single, vertical downpipe. Seven different overflow configurations, each with five different downpipe lengths, are investigated in terms of maximum flowrate and corresponding water depth in the gutter. The results of this study are significant in that they do not support the common theoretical assumption that there is a limiting length of a siphonic downpipe over which pipe-full flow may occur before gravity causes the water to accelerate enough for it to no longer occupy the full cross-sectional area. Instead, this study has found that once a downpipe is flowing full, it is possible for pipe-full flow conditions to be maintained over the entire pipe length.

Estimating flow rates through individual outlets of siphonic roof drainage systems

An experimental investigation is used to quantify the flow rates through individual outlets of multi-outlet siphonic roof drainage systems under both full-pipe and partially filled pipe flow conditions. A pressure transducer and a propeller-type current meter were installed within each tailpipe to measure water depth and flow velocity. The study tests the hypothesis that it may be possible to predict accurately the flow rates through individual outlets of multi-outlet siphonic roof drainage systems. A new technique of estimating flow rates is trialled by comparing instantaneous pressure transducer and current meter readings with previously calibrated flow data to find the best data match. The study results were very positive and clearly demonstrate that the underlying methodology was appropriate and that it may be possible to model numerically the individual outlet flow rates in multi-outlet siphonic roof drainage systems.

Site investigation of damages occurred in a steel space truss roof structure due to ponding

In this study, a steel space truss roof structure which was partially collapsed after a local meteorological event that produced strong winds and heavy rains in Marmara region was investigated. For this purpose, damage reconnaissance studies were conducted and findings observed in the site were interpreted according to the current Turkish steel building design codes based on allowable stress design. For the structural members taken from debris, material tests were conducted. This steel space truss roof structure covering an industrial facility was supported on reinforced concrete columns of 11m height, sheathed by using fibro panel with membrane, having a slope of 1% to monitor the waterflow to the siphonic roof drainage system and surrounded by the parapets of 15 and 25cm heights at the roof-edges. As a result of the investigation, it was estimated that during this extreme rainfall event, due to any deficiency or blockage of the roof drainage system in the edge zones with parapets of the roof, rainwater accumulation occurred at these regions of the roof fully and eventually due to the ponding which is a particular loading case for the design of the structures that is however not defined by the Turkish design standards, roof collapse of this industrial hall building occurred partially.

Air water flows in building drainage systems

This paper investigates the mechanisms of two-phase flows that occur in commercial and industrial roof drainage systems. Both traditional gravity-fed and siphonic roof drainage systems are examined.Air entrainment plays a fundamental role in the performance of siphonic roof drainage systems. In particular, air entrainment has a significant effect on:maximum system flowrate capacity;pipe friction losses;operational system pressures;operational gutter water depths; andability of the system to prime.However, experimental results presented here demonstrate that the reduction in system capacity is not directly proportional to the increase in air content. One possible explanation for this is that water and air will be affected differently by sub-atmospheric pressures. The effect air entrainment has on roof drainage performance is investigated. The ways in which air is introduced into the system are identified and the effects of different air/water ratios are quantified. Finally methods for reducing air entrainment are described.

Novel modulated flow, self configuring, siphonic roof drainage system

Siphonic roof drainage systems are an efficient method of removing rainwater rapidly from roofs. Siphonic roof drainage systems are designed to run full-bore, resulting in sub-atmospheric system pressures, higher driving heads and higher system flow velocities. Hence, siphonic roof drainage systems normally require far fewer downpipes, and the depressurised conditions also mean that much of the collection pipework can be routed at high level, thus reducing the extent of any underground pipework. But, they work properly at only one roof run-off rate and therefore suffer from sizing and operational problems that limit their performance. Climate change is creating situations where normal ranges of rainfall intensity are being frequently exceeded, and this may have an impact on the performance of siphonic roof drainage systems. A multiple parallel pipe siphonic roof drainage system appears to offer benefits and avoids sizing problems associated with current siphonic roof drainage systems. A movable cap covering the inlet to a small bank of parallel pipes has the potential to avoid noise associated with making and breaking siphonic action through flow modulation. Laboratory scale tests demonstrate the basic feasibility of the multiple parallel pipe system and indicate that handover of flow between pipes occurs smoothly and that the flow modulation cap functions reliably. This technology includes moving parts and smaller diameters (19 mm ID) than are currently accepted (32 mm ID) in the British Standards and product development will be required. Practical application: Original research detailing an innovative development of a multi-pipe siphonic roof drainage system. This provides a wide design flow rate range and flow modulation caps reduce noise significantly by avoiding priming failure. Potentially extends the technique to a smaller building size than with current siphonic systems and offers climate change resilience potential.

Investigation of a Flow Modulation System for Siphonic Roof Drainage Systems

Siphonic roof drainage systems (SRDS’s) have been widespread used now for approximately 40 years and are an efficient method of removing rainwater rapidly from roofs. SRDS’s are designed to run full-bore, resulting in sub-atmospheric system pressures with high hydraulic driving heads and higher system flow velocities than conventionally guttered systems. Hence, SRDS’s normally require far fewer downpipes, and the depressurised conditions also mean that much of the collection pipework can be routed at a high level, thus reducing the extent of any underground pipework. But, they work properly at only one roof run-off rate and therefore suffer from sizing and operational problems including noise and vibration which limit their performance and adoption rate. Climate change is creating situations where normal ranges of rainfall intensity are being frequently exceeded, so the typical:storm ratios (rTS) are large increasing. Current SRDS’s typically operate within a small rTS range of 2. This may have an impact on the future uptake of SRDS’s. This paper describes the development of a novel SRDS which includes a small mobile cap at the roof of outlet appears to offer benefits and avoids sizing problems associated with current SRDS’s. The cap has the potential to avoid noise associated with making and breaking siphonic action through flow modulation. Laboratory scale tests demonstrate the basic feasibility of the cap system and indicate that the cap functions reliably. This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Basic on sizing and design optimiza-tion factors are suggested. The rTS range is increased from approximately 2 to approximately 6.

Property-level stormwater drainage systems: integrated flow simulation and whole-life costs

Property-level stormwater drainage systems consist of roof drainage systems and those systems that connect buildings and their surrounding ground surfaces to main sewer networks, on-site rainwater harvesting or other capture systems. The design of these local systems has traditionally been based on simplistic approaches that fail to account for performance and integration. Given the extra demands associated with climate change, these limitations will take on increasing importance due to the potential for site-level flooding or water damage. To address the concerns, new tools are needed to describe and assess performance as well as to enable a more integrated approach. Research is presented on the development of an integrated property-level drainage simulation model and associated whole-life costing model. Application of the model illustrates the importance of accounting for flow interactions in order to assess the hydraulic effectiveness of different adaptation schemes. Similarly, the whole-life cost model can determine the through-life costs of adaptation strategies, hence enabling the assessment of the cost effectiveness of integrated designs. Les systèmes d'écoulement des eaux pluviales au niveau des biens immobiliers se composent de systèmes d'écoulement des eaux de toiture et de systèmes qui raccordent les bâtiments et leurs surfaces au sol environnantes aux réseaux d'égouts, aux systèmes de collecte des eaux pluviales sur place ou aux autres systèmes de récupération des eaux. La conception de ces systèmes locaux a été basée traditionnellement sur des approches simplistes qui sont incapables de rendre compte des performances et de l'intégration. Etant donné les exigences supplémentaires liées au changement climatique, ces limites prendront une importance croissante en raison des risques potentiels d'inondation ou de dégât des eaux au niveau du site. Pour répondre à ces préoccupations, de nouveaux outils sont nécessaires afin de décrire et d'évaluer les performances, ainsi que de permettre une approche plus intégrée. Il est présenté des recherches sur la mise au point d'un modèle intégré de simulation d'écoulement des eaux au niveau d'un bien immobilier et un modèle associé d'estimation du coût global du cycle de vie. L'application de ce modèle illustre l'importance de la prise en compte des interactions des flux afin d'évaluer l'efficacité hydraulique des différents programmes d'adaptation. De manière similaire, le modèle du coût global du cycle de vie est capable de déterminer le coût global des stratégies d'adaptation, permettant ainsi d'évaluer la rentabilité des conceptions intégrées. Mots clés: services du bâtiment, conception du système d'écoulement des eaux, systèmes d'écoulement des eaux, écoulement local des eaux, toitures, écoulement des eaux pluviales, coût global du cycle de vie

Property-based rainwater drainage design and the impacts of climate change

Property-based rainwater drainage provision comprises a number of components broadly categorised as roof, surface or underground drainage. These systems are relied upon to prevent water ingress to the building and to avoid localised ponding or flooding. Recognition of the inherently unsteady response of the integrated network, in part driven by a particular rainfall event but also due to the transient nature of the fluid flows therein, is important in allowing an understanding of system performance under both current and future climate conditions. Codes and standards suggest that roof drainage systems, conventional or siphonic, are designed using a single rainfall intensity figure, representative of the most intense part of a longer storm, whereas runoff to surface and underground drainage is typically based on a single-peaked rainfall profile. Together with the difference in event duration typically adopted as part of the design process, this means that, unless a straightforward uplift factor is applied, then understanding the potential impacts of climate change on overall system performance can be difficult. Using numerical modelling techniques to analyse the performance of a case study site located in Edinburgh, this research identifies an appropriate common rainfall event from which a system-specific exceedance threshold is identified. Specification of this rainfall intensity facilitates an exploration of the impacts of climate change undertaken within the context of UKCP09 projections. Using gutter overtopping as an indicator of failure, this paper explores possible changes in the frequency of system under-capacity under varying future climate change scenarios. Practical application: Engineers are encouraged, in relevant codes and standards, to take account of the potential impacts of climate change when designing rainwater drainage systems for buildings. However, little guidance is offered therein on how to achieve this. This paper presents an example of UKCP09 climate change projections, specifically Weather Generator precipitation data, applied to a case study site that integrates roof, surface and underground drainage networks. Results illustrate the possible change in frequency of system failure, identified in this case as gutter overtopping.

Measuring flows in partially-filled pipes in siphonic roof drainage systems

While a variety of flow measurement devices are available to measure the flow of water through closed pipe systems, these devices generally only function correctly when the pipes are completely full of water. Accurate measurement of water flows in partially-filled pipes is extremely difficult. In siphonic drainage systems, this problem is further compounded by the unsteady flow conditions that occur in the pipework during the priming process. This has been a major obstacle to understanding the performance of these systems in practice. In order to accurately model the priming process in multioutlet siphonic roof drainage systems, a method of estimating the instantaneous flows through the partially-filled individual pipes needs to be developed. This paper describes an experimental method of determining flows in partially-filled pipes using a propeller-type current meter to measure flow velocity and a pressure transducer to measure water depth and a modified version of the continuity equation. A computational model is presented which estimates the unsteady flows passing through partially-filled pipework. Overall, the experimental results are promising and correspond well with the model. The results of this study will ultimately be used to develop an unsteady flow model of the priming process in multi-outlet siphonic roof drainage systems.

Plastic pipe pressures in siphonic roof drainage systems

Siphonic roof drainage is a highly efficient type of drainage system that is particularly suitable for large buildings and other structures over approximately 4 m in height. Although siphonic roof drainage systems are enjoying ever-increasing popularity with architects, there is still some uncertainty regarding the minimum pipe pressure class required for siphonic pipework, especially in tall buildings. This is particularly the case in warmer countries since higher temperatures can drastically decrease the strength of the pipework material used in siphonic systems – typically unplasticized polyvinylchloride (PVC-U) and high-density polyethylene (HDPE). However, there is very limited information available on how plastic pipes behave under the sub-atmospheric pressures that occur under operating conditions in siphonic systems. This paper describes experiments conducted to investigate sub-atmospheric pressures in siphonic systems and how they may be controlled by injecting air into vertical downpipes. Recommendations for minimum pipework pressure classes are provided together with methods for limiting the minimum pressures without significantly decreasing the system capacity. This paper will help engineers design siphonic systems with more confidence so that such systems will continue to perform adequately over their intended design life. L’évacuation siphonique des eaux de toit est un type de système d’évacuation des eaux hautement performant, qui est particulièrement adapté aux grands immeubles et autres structures dépassant 4 m de hauteur environ. Bien que les systèmes d’évacuation siphonique des eaux de toit bénéficient d’une popularité sans cesse croissante auprès des architectes, il existe encore quelque incertitude quant à la classe de pression minimale des tuyaux nécessaire pour les tuyauteries siphoniques, surtout dans les grands immeubles. Ceci est tout particulièrement le cas dans les pays plus chauds, dans la mesure où des températures plus élevées peuvent considérablement réduire la résistance du matériau utilisé pour les tuyauteries dans les systèmes siphoniques – généralement du polychlorure de vinyle non plastifié (PVC-U) et du polyéthylène haute densité (PEHD). Les informations disponibles sont cependant très limitées concernant la manière dont se comportent les tuyaux en plastique soumis aux pressions sub-atmosphériques qui se rencontrent dans les conditions de fonctionnement des systèmes siphoniques. Cet article décrit des expériences conduites afin d’étudier les pressions sub-atmosphériques dans les systèmes siphoniques et la façon dont elles peuvent être contrôlées en injectant de l’air dans les tuyaux de descente des eaux pluviales. Des recommandations concernant les classes de pression minimales des tuyauteries sont fournies, ainsi que des méthodes pour limiter les pressions minimales sans abaissement significatif de la capacité des systèmes. Cet article aidera les ingénieurs à concevoir avec plus d’assurance des systèmes siphoniques de façon à ce que ces systèmes puissent continuer à fonctionner convenablement tout au long de leur durée de vie nominale prévue. Mots clés: pression critique de flambage, pression négative, évacuation siphonique des eaux de toit

Aeration and gutter water levels in siphonic roof drainage systems

An investigation is presented into how negative system pressures, the degree of aeration, and gutter water levels are affected by the number of outlets in a siphonic roof drainage system. The experimental results show that system pressures decrease if outlets are blocked. It is also shown that the depth of water above an outlet is strongly influenced by the negative pressure acting at the outlet. As the suction effect at the outlet increases, due to lower system pressures, more water and air will be drawn into the outlets and this will result in a corresponding increase in overall gutter water depth. The results also show that there is often built-in redundancy in multiple outlet siphonic systems experiencing lower-intensity rainfall events, and if one or two outlets were blocked, the system would still operate satisfactorily. A new outlet suppressor was trialled and this was shown to reduce gutter water levels by up to 58% at some positions in the gutter. Il est présenté une enquête sur la manière dont les pressions négatives dans le système concerné, le degré d'aération et les niveaux d'eau dans les chéneaux sont affectés par le nombre d'orifices de sortie dans un système d'écoulement des eaux de toit par siphonnage. Les résultats expérimentaux montrent que les pressions dans le système diminuent si des orifices de sortie sont obturés. Il est également montré que la profondeur de l'eau au-dessus d'un orifice de sortie est fortement influencée par la pression négative s'exerçant à l'orifice de sortie. Plus l'effet de succion à l'orifice de sortie augmente, en raison des pressions plus faibles dans le système, et plus les quantités d'air et d'eau entraînées dans les orifices de sortie seront importantes, et cela aura pour résultat une augmentation correspondante de la profondeur générale de l'eau dans les chéneaux. Les résultats montrent également qu'il existe souvent une redondance intégrée dans les systèmes à siphons comportant des orifices de sortie multiples et soumis à des épisodes pluvieux de faible intensité, et que si un ou deux orifices de sortie sont obturés, le système fonctionne encore de manière satisfaisante. Un nouvel obturateur d'orifice de sortie a été essayé, ce qui a permis de montrer que celui-ci réduit dans une proportion allant jusqu'à 58 % en certains points les niveaux d'eau dans les chéneaux. Mots clés: aération, niveaux d'eau dans les chéneaux, pressions négatives, écoulement des eaux de toit par siphonnage