O objetivo do presente trabalho é avaliar a microestrutura e as propriedades da superliga MAR-M247 modificada com nióbio (composição nominal: 10,2% em peso Co; 10,2W; 8,5Cr; 5,6Al; 1,6Nb; 1,4Hf; 1,1Ti; 0,7Mo; 0,15C; 0,06Zr; 0,015B; Ni balanço) submetida a diferentes rotas de processamento (tratamento térmico, laser cladding e oxidação isotérmica). O material foi produzido por fusão por indução a vácuo na empresa Açotécnica S.A. (Jandira/SP). As amostras no estado bruto de fusão e tratadas termicamente (solubilização e envelhecimento em uma e duas etapas por diferentes temperaturas e tempos) foram analisadas por MEV e MEV-FEG com EDS. Também foram realizadas medidas de análise térmica diferencial (DTA), dureza, difração de raios X e simulações em Thermo-Calc, JMatPro e PandaT. Em outra parte desta tese, realizada no Instituto Superior Técnico em Lisboa/Portugal, as amostras da superliga MAR-M247(Nb) foram fundidas pela técnica de laser melting e caracterizadas por MEV-FEG, EDS, dureza e EBSD, além de diversos cálculos envolvendo os parâmetros de processo utilizados. Além disso, os experimentos de deposição de pós de NiCr, NiCrAl e NiCrAlY no substrato da superliga MAR-M247(Nb) utilizando a técnica de laser cladding permitiram calcular alguns parâmetros geométricos e analisar a microestrutura dos depósitos (MEV-FEG, EDS e medidas de dureza) após o processamento e os tratamentos térmicos. Na última parte desta tese, foram realizados ensaios de oxidação isotérmica a 1000°C por até 216 horas (ar estático) na superliga MAR-M247(Nb). As amostras oxidadas (superfície e seção transversal) foram analisadas por MEV, medidas por EDS (pontual, line scan e mapeamento) e difração de raios X, além de cálculos das constantes kp e n. Os resultados desta tese permitem comparar as temperturas solvus de ?\' (1210oC), solidus (1310oC) e liquidus (1360oC) obtidas por Thermo-Calc com as temperaturas solvus de ?\' (1238oC), de fusão incipiente (1281oC) e liquidus (1370oC) obtidas por experimentos de análise térmica diferencial para a superliga MAR-M247(Nb). A microestrutura da superliga MARM247(Nb) no estado bruto de fusão é dendrítica com carbetos de W, Ti, Nb e Hf nas regiões interdendríticas. O tratamento de solubilização a 1260°C por 8 horas foi escolhido como condição ideal, enquanto que o tratamento de envelhecimento a 980°C por 80 horas apresentou o maior tamanho de partícula de ?\'. O material fundido pela técnica de laser melting apresentou trincas devido à formação de regiões eutéticas ?/?\' de baixo ponto de fusão. A microestrutura dos depósitos de NiCr, NiCrAl e NiCrAlY as clad é dendrítica com a fase solução sólida ?-Ni(Cr), além de poros e óxidos/carbetos. O depósito de NiCrAlY possui fases ricas em ítrio. A amostra de NiCr tratada 1150oC por 50 horas não apresentou evidências de segregação enquanto que as amostras de NiCrAl e NiCrAlY apresentaram a fase ?\' precipitada fina e uniformemente após tratamento térmico a 1100 e 1150°C por 10 e 50 horas. A estrutura da camada óxida da superliga MAR-M247(Nb) submetida a ensaios de oxidação isotérmica a 1000°C por até 216 horas consiste de NiO na camada externa, Cr2O3, TiO2, CoO, espinélios de (Ni,Co)Cr2O4 e partículas de W20O58 e HfO2 na camada intermediária e Al2O3 na camada interna. Finalmente, conclui-se que a microestrutura e as propriedades da superliga MAR-M247(Nb) são alteradas quando as rotas de processamento (tratamento térmico, laser cladding e oxidação isotérmica) mudam. / The aim of this work is to evaluate the microstructure and the properties of the niobiummodified MAR-M247 superalloy (nominal composition: 10.2 weight percent of Co; 10.2W; 8.5Cr; 5.6Al; 1.6Nb; 1.4Hf; 1.1Ti; 0.7Mo; 0.15C; 0.06Zr; 0.015B; Ni balance) submitted to different processing routes (heat-treatment, laser cladding and isothermal oxidation). The material was produced by vacuum induction melting at Açotécnica Company (Jandira/SP). The as-cast and heat-treated samples (solution and aging in one and two steps at different temperatures and times) were analyzed in SEM and FEG-SEM with EDX. Differential thermal analysis (DTA), hardness, X-ray diffraction and simulations with Thermo-Calc, JMatPro and PandaT were performed as well. In another part of this thesis, performed at Instituto Superior Técnico in Lisbon/Portugal, the samples of the MAR-M247(Nb) superalloy were produced by laser melting technique and characterized by FEG-SEM, EDX, hardness, and EBSD, besides some calculations involving the process parameters utilized. Furthermore, the experiments of NiCr, NiCrAl and NiCrAlY powder deposition on the substrate of MAR-M247(Nb) superalloy utilizing the laser cladding technique allowed the calculation of some geometric parameters, as well as the analysis of the microstructure of the deposits (FEG-SEM, EDX and hardness) after the processing and the heat-treatments. In the last part of this work, experiments of isothermal oxidation at 1000°C for up to 216 hours (static air) were performed in the MAR-M247(Nb) superalloy. The oxidized samples (surface and cross-section) were analyzed by SEM, EDX (punctual, line scan and mapping) and X-ray diffraction, besides some calculations of kp and n constants. The results of this thesis allow comparing the ?\' solvus (1210oC), solidus (1310oC) and liquidus (1360oC) temperatures obtained by Thermo-Calc with the ?\' solvus (1238oC), incipient melting (1281oC) and liquidus (1370oC) temperatures obtained by differential thermal analysis experiments of the MARM247(Nb) superalloy. The microstructure of the as-cast MAR-M247(Nb) superalloy is dendritic with W, Ti, Nb and Hf carbides in the interdendritic regions. The solution heattreatment at 1260°C for 8 hours was chosen as the ideal condition, whilst the aging heattreatment at 980°C for 80 hours presented the highest ?\' particle size. The material processed by laser melting technique showed cracks due to formation of low melting point ?/?\' eutectic regions. The microstructure of the NiCr, NiCrAl and NiCrAlY as clad deposits is dendritic with the ?-Ni(Cr) solid solution phase, besides pores and oxides/carbides. The NiCrAlY deposit has yttrium-rich phases. The NiCr sample heattreated at 1150oC for 50 hours didn\'t present evidences of segregation whilst the NiCrAl and NiCrAlY samples presented fine and uniform ?\' phase precipitated after the heattreatment at 1100 and 1150°C for 10 and 50 hours. The structure of the oxide layer of the MAR-M247(Nb) superalloy submitted to isothermal oxidation experiments at 1000°C for up to 216 hours has NiO in the outer layer, Cr2O3, TiO2, CoO, (Ni,Co)Cr2O4 spinels and W20O58 and HfO2 particles in the intermediate layer, and Al2O3 in the inner layer. Finally, it is possible to conclude that the microstructure and the properties of the MAR-M247(Nb) superalloy are modified when the processing routes (heat-treatment, laser cladding and isothermal oxidation) are changed.

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O objetivo do presente trabalho é avaliar a microestrutura e as propriedades da superliga MAR-M247 modificada com nióbio (composição nominal: 10,2% em peso Co; 10,2W; 8,5Cr; 5,6Al; 1,6Nb; 1,4Hf; 1,1Ti; 0,7Mo; 0,15C; 0,06Zr; 0,015B; Ni balanço) submetida a diferentes rotas de processamento (tratamento térmico, laser cladding e oxidação isotérmica). O material foi produzido por fusão por indução a vácuo na empresa Açotécnica S.A. (Jandira/SP). As amostras no estado bruto de fusão e tratadas termicamente (solubilização e envelhecimento em uma e duas etapas por diferentes temperaturas e tempos) foram analisadas por MEV e MEV-FEG com EDS. Também foram realizadas medidas de análise térmica diferencial (DTA), dureza, difração de raios X e simulações em Thermo-Calc, JMatPro e PandaT. Em outra parte desta tese, realizada no Instituto Superior Técnico em Lisboa/Portugal, as amostras da superliga MAR-M247(Nb) foram fundidas pela técnica de laser melting e caracterizadas por MEV-FEG, EDS, dureza e EBSD, além de diversos cálculos envolvendo os parâmetros de processo utilizados. Além disso, os experimentos de deposição de pós de NiCr, NiCrAl e NiCrAlY no substrato da superliga MAR-M247(Nb) utilizando a técnica de laser cladding permitiram calcular alguns parâmetros geométricos e analisar a microestrutura dos depósitos (MEV-FEG, EDS e medidas de dureza) após o processamento e os tratamentos térmicos. Na última parte desta tese, foram realizados ensaios de oxidação isotérmica a 1000°C por até 216 horas (ar estático) na superliga MAR-M247(Nb). As amostras oxidadas (superfície e seção transversal) foram analisadas por MEV, medidas por EDS (pontual, line scan e mapeamento) e difração de raios X, além de cálculos das constantes kp e n. Os resultados desta tese permitem comparar as temperturas solvus de ?\' (1210oC), solidus (1310oC) e liquidus (1360oC) obtidas por Thermo-Calc com as temperaturas solvus de ?\' (1238oC), de fusão incipiente (1281oC) e liquidus (1370oC) obtidas por experimentos de análise térmica diferencial para a superliga MAR-M247(Nb). A microestrutura da superliga MARM247(Nb) no estado bruto de fusão é dendrítica com carbetos de W, Ti, Nb e Hf nas regiões interdendríticas. O tratamento de solubilização a 1260°C por 8 horas foi escolhido como condição ideal, enquanto que o tratamento de envelhecimento a 980°C por 80 horas apresentou o maior tamanho de partícula de ?\'. O material fundido pela técnica de laser melting apresentou trincas devido à formação de regiões eutéticas ?/?\' de baixo ponto de fusão. A microestrutura dos depósitos de NiCr, NiCrAl e NiCrAlY as clad é dendrítica com a fase solução sólida ?-Ni(Cr), além de poros e óxidos/carbetos. O depósito de NiCrAlY possui fases ricas em ítrio. A amostra de NiCr tratada 1150oC por 50 horas não apresentou evidências de segregação enquanto que as amostras de NiCrAl e NiCrAlY apresentaram a fase ?\' precipitada fina e uniformemente após tratamento térmico a 1100 e 1150°C por 10 e 50 horas. A estrutura da camada óxida da superliga MAR-M247(Nb) submetida a ensaios de oxidação isotérmica a 1000°C por até 216 horas consiste de NiO na camada externa, Cr2O3, TiO2, CoO, espinélios de (Ni,Co)Cr2O4 e partículas de W20O58 e HfO2 na camada intermediária e Al2O3 na camada interna. Finalmente, conclui-se que a microestrutura e as propriedades da superliga MAR-M247(Nb) são alteradas quando as rotas de processamento (tratamento térmico, laser cladding e oxidação isotérmica) mudam. / The aim of this work is to evaluate the microstructure and the properties of the niobiummodified MAR-M247 superalloy (nominal composition: 10.2 weight percent of Co; 10.2W; 8.5Cr; 5.6Al; 1.6Nb; 1.4Hf; 1.1Ti; 0.7Mo; 0.15C; 0.06Zr; 0.015B; Ni balance) submitted to different processing routes (heat-treatment, laser cladding and isothermal oxidation). The material was produced by vacuum induction melting at Açotécnica Company (Jandira/SP). The as-cast and heat-treated samples (solution and aging in one and two steps at different temperatures and times) were analyzed in SEM and FEG-SEM with EDX. Differential thermal analysis (DTA), hardness, X-ray diffraction and simulations with Thermo-Calc, JMatPro and PandaT were performed as well. In another part of this thesis, performed at Instituto Superior Técnico in Lisbon/Portugal, the samples of the MAR-M247(Nb) superalloy were produced by laser melting technique and characterized by FEG-SEM, EDX, hardness, and EBSD, besides some calculations involving the process parameters utilized. Furthermore, the experiments of NiCr, NiCrAl and NiCrAlY powder deposition on the substrate of MAR-M247(Nb) superalloy utilizing the laser cladding technique allowed the calculation of some geometric parameters, as well as the analysis of the microstructure of the deposits (FEG-SEM, EDX and hardness) after the processing and the heat-treatments. In the last part of this work, experiments of isothermal oxidation at 1000°C for up to 216 hours (static air) were performed in the MAR-M247(Nb) superalloy. The oxidized samples (surface and cross-section) were analyzed by SEM, EDX (punctual, line scan and mapping) and X-ray diffraction, besides some calculations of kp and n constants. The results of this thesis allow comparing the ?\' solvus (1210oC), solidus (1310oC) and liquidus (1360oC) temperatures obtained by Thermo-Calc with the ?\' solvus (1238oC), incipient melting (1281oC) and liquidus (1370oC) temperatures obtained by differential thermal analysis experiments of the MARM247(Nb) superalloy. The microstructure of the as-cast MAR-M247(Nb) superalloy is dendritic with W, Ti, Nb and Hf carbides in the interdendritic regions. The solution heattreatment at 1260°C for 8 hours was chosen as the ideal condition, whilst the aging heattreatment at 980°C for 80 hours presented the highest ?\' particle size. The material processed by laser melting technique showed cracks due to formation of low melting point ?/?\' eutectic regions. The microstructure of the NiCr, NiCrAl and NiCrAlY as clad deposits is dendritic with the ?-Ni(Cr) solid solution phase, besides pores and oxides/carbides. The NiCrAlY deposit has yttrium-rich phases. The NiCr sample heattreated at 1150oC for 50 hours didn\'t present evidences of segregation whilst the NiCrAl and NiCrAlY samples presented fine and uniform ?\' phase precipitated after the heattreatment at 1100 and 1150°C for 10 and 50 hours. The structure of the oxide layer of the MAR-M247(Nb) superalloy submitted to isothermal oxidation experiments at 1000°C for up to 216 hours has NiO in the outer layer, Cr2O3, TiO2, CoO, (Ni,Co)Cr2O4 spinels and W20O58 and HfO2 particles in the intermediate layer, and Al2O3 in the inner layer. Finally, it is possible to conclude that the microstructure and the properties of the MAR-M247(Nb) superalloy are modified when the processing routes (heat-treatment, laser cladding and isothermal oxidation) are changed.

Dans l’industrie de la verrerie, le laser cladding est une technique de rechargement très innovante permettant de déposer une couche très fine d’un alliage à base de nickel pour protéger les moules (utiles à la fabrication de bouteilles en verre) de la corrosion, de l’abrasion ainsi que de la fatigue thermique. La méthode utilisée ici (fusion de poudre projetée par laser) est très courante en fabrication additive. Cette étude s’intéresse à l’impact du rechargement sur le dépôt et les substrats en Cu-Ni-Al et en fonte GL. L’influence sur la microstructure ainsi que sur le comportement mécanique a pu être étudiée (MEB et microanalyses, dureté, contraintes résiduelles ...). Nous nous sommes focalisés sur l’apparition de défauts tels que le manque d’accroche lors du laser cladding sur du Cu-Ni-Al et sur la possible fissuration lors du rechargement sur de la fonte GL. Le but est bien sûr de s’affranchir de ces défauts. Il a notamment été mis en évidence que le manque d’accroche (cas du Cu-Ni-Al) est lié à la distribution gaussienne de la poudre qui atténue la puissance incidente du laser au niveau du pic de poudre. Le manque d'accroche n'est pas détecté sur le substrat en fonte en raison de sa forte absorptivité et de sa faible conductivité thermique. Néanmoins, des fissures peuvent être observées en raison de contraintes résiduelles thermiques et de la présence d'une zone affectée thermiquement. De plus, l’analyse statistique ANOVA a permis une optimisation des paramètres de rechargement de telle sorte à obtenir une accroche dans toute la section tout en respectant les préconisations géométriques données par les Établissements CHPOLANSKY pour le cordon. / In glass industry, the laser cladding is an innovative surfacing technique allowing to deposit a very thin layer of nickel to protect glass mold (useful for glass bottle production) against corrosion, abrasion and thermal fatigue. This method (powder fusion by projection) is well known in additive manufacturing. The aim of this work is to observe the impact of the laser cladding on the coating behavior but also on the Cu-Ni-Al and flake-graphite cast iron substrates. The microstructure and the mechanical properties were studied (SEM and microanalysis, microhardness, residual stress …) around the interface cladding/substrate. The work was also focused on the defects like lack of bonding but also on cracking behavior during surfacing on cast iron. The purpose was to prevent from those defects. This work showed that the lack of bonding to the Cu-Ni-Al substrate is due to the gaussian distribution of the powder which attenuates the input laser power at its peak. The lack of bonding is not detected on cast iron substrate thanks to its high absorptivity and low thermal conductivity. Nevertheless, cracks can be observed due to thermal residual stresses and the presence of a thermal affected zone. The ANOVA technique allowed us to optimize the processing parameters in order to obtain a perfect bonding and the geometry wanted by CHPOLANSKY Establishments.

A newly developed martensitic stainless steel powder, called “powder A”, designed for surface coating with laser cladding and PTA cladding was characterized. The purpose with powder A is to achieve both good corrosion resistance and wear resistance in a stainless steel grade. The investigation of powder A was divided into cladding characterization, microstructural investigation and a property comparison to existing grades 316 HSi and 431 L. Powder A was successfully deposited with laser cladding, exhibiting a wide process window, and PTA cladding. In both cases no preheating was required and no cracks were formed. The microstructure examination indicates that powder A has a martensitic structure possibly containing small amounts of ferrite in the grain boundaries. Thermodynamic calculations in computer software Thermo-Calc 4.1 supported this theory. The microstructure of powder A proved to be very stable over a wide range of cladding parameters. Powder A was significantly harder than 316 HSi and 431 L and had better corrosion resistance than 431 L in a chloride environment. Powder A had similar corrosion properties as 316 HSi in the experiments made .The wear performance of the powder A coatings was similar to 431 L. This was surprising since the hardness of the powder A coatings is significantly higher compared to 431 L.

Structural engineering is facing an extraordinarily challenging era. These challenges are driven by the increasing expectations of modern society to provide low-cost, architecturally appealing structures which can withstand large earthquakes. However, being able to avoid collapse in a large earthquake is no longer enough. A building must now be able to withstand a major seismic event with negligible damage so that it is immediately occupiable following such an event. As recent earthquakes have shown, the economic consequences of not achieving this level of performance are not acceptable. Technological solutions for low-damage structural systems are emerging. However, the goal of developing a low-damage building requires improving the performance of both the structural skeleton and the non-structural components. These non-structural components include items such as the claddings, partitions, ceilings and contents. Previous research has shown that damage to such items contributes a disproportionate amount to the overall economic losses in an earthquake. One such non-structural element that has a history of poor performance is the external cladding system, and this forms the focus of this research. Cladding systems are invariably complicated and provide a number of architectural functions. Therefore, it is important than when seeking to improve their seismic performance that these functions are not neglected. The seismic vulnerability of cladding systems are determined in this research through a desktop background study, literature review, and postearthquake reconnaissance survey of their performance in the 2010 – 2011 Canterbury earthquake sequence. This study identified that precast concrete claddings present a significant life-safety risk to pedestrians, and that the effect they have upon the primary structure is not well understood. The main objective of this research is consequently to better understand the performance of precast concrete cladding systems in earthquakes. This is achieved through an experimental campaign and numerical modelling of a range of precast concrete cladding systems. The experimental campaign consists of uni-directional, quasi static cyclic earthquake simulation on a test frame which represents a single-storey, single-bay portion of a reinforced concrete building. The test frame is clad with various precast concrete cladding panel configurations. A major focus is placed upon the influence the connection between the cladding panel and structural frame has upon seismic performance. A combination of experimental component testing, finite element modelling and analytical derivation is used to develop cladding models of the cladding systems investigated. The cyclic responses of the models are compared with the experimental data to evaluate their accuracy and validity. The comparison shows that the cladding models developed provide an excellent representation of real-world cladding behaviour. The cladding models are subsequently applied to a ten-storey case-study building. The expected seismic performance is examined with and without the cladding taken into consideration. The numerical analyses of the case-study building include modal analyses, nonlinear adaptive pushover analyses, and non-linear dynamic seismic response (time history) analyses to different levels of seismic hazard. The clad frame models are compared to the bare frame model to investigate the effect the cladding has upon the structural behaviour. Both the structural performance and cladding performance are also assessed using qualitative damage states. The results show a poor performance of precast concrete cladding systems is expected when traditional connection typologies are used. This result confirms the misalignment of structural and cladding damage observed in recent earthquake events. Consequently, this research explores the potential of an innovative cladding connection. The outcomes from this research shows that the innovative cladding connection proposed here is able to achieve low-damage performance whilst also being cost comparable to a traditional cladding connection. It is also theoretically possible that the connection can provide a positive value to the seismic performance of the structure by adding addition strength, stiffness and damping. Finally, the losses associated with both the traditional and innovative cladding systems are compared in terms of tangible outcomes, namely: repair costs, repair time and casualties. The results confirm that the use of innovative cladding technology can substantially reduce the overall losses that result from cladding damage.

The cladding industry is relatively independent and complex, having contemporary features in a rapidly changing sector of the construction industry. The increasing complexity of the cladding procurement and fragmentation of the supply chain bring challenges for making informed decisions. The purpose of this research was to study the cladding design and procurement process, in particular the decision making process. It was hoped to develop an integrated decision making mechanism within the context of the cladding supply chain. Based on preliminary exploration, a conceptual model of integrated communication and decision-making (ICDM) was proposed. Within this model, an Information and Communication (I&C) Hub acts as the pivotal platform of the information supply and communication in the supply chain and is managed by an industry level third party. It provides an effective and secure approach to information exchange and collaborative decision making. A questionnaire survey was the key method of this research, while industry meetings and informal interviews were employed to provide in-depth understanding of the communication related issues in the industry. It was found that the participants of the cladding supply chain were experiencing difficulties of identifying information sources and accessing information, and that an industry level third party acting as an independent information source could be accepted by the cladding industry. Therefore, the I&C Hub gained its necessity and partial feasibility. It was also found that training opportunity for practitioners was limited and the usage of ICT had a large potential for improvement. A number of modifications on the I&C Hub and information flows within the ICDM were proposed to enhance its practicality, and the enhanced model was presented and evaluated by an industry meeting. The conceptual model can only be completely validated by real cases; therefore, this study concluded with a recommendation for testing the framework in future pilot projects.

Control of moisture and heat flow through building enclosure assemblies is a critical component of overall building performance. This thesis shows that significant drying of moisture in wall assemblies is possible and that ventilation of cladding significantly increases the rate of drying in some assemblies without having detrimental impact on the enclosures thermal performance. A review found that thermal and moisture buoyancy, wind pressure gradients and mechanical equipment drive ventilation airflow. This ventilation flow can theoretically increase the effective water vapour permeance and thermal conductivity. Ventilation has the potential to increase outward drying through relatively impermeable claddings at the low flows expected to occur in service. The impact on thermal conductance is much less. A methodology for assessing the complicated airflow resistance characteristics of lap sidings was developed and applied to a representative vinyl siding. Field drying studies showed that the sample tested is well ventilated. Field brick veneer clad wall samples were also tested for system airflow resistance over a range of driving pressures. Theoretical predictions under-estimated the measured flow rate for given steady driving air pressures. Measurements of naturally driven cavity air speeds and smoke pencil testing showed that flow rates were commonly occurring that would in theory significantly affect the hygrothermal performance of the walls. This was confirmed with field drying studies. A field drying study of east-facing test wall with vinyl siding and brick veneer cladding was conducted in Waterloo, Ontario, Canada. Significant amounts of drying and inward moisture redistribution were measured. Wall sheathing dried quickly in hot summer conditions but in some cases significant inward driven moisture flow occurred. In cool and cold weather the wall dried more slowly and much less moisture moved inward. Increased cladding ventilation significantly increased drying rates and reduced internal wall assembly moisture levels. It was concluded that cladding ventilation acts to increase the effective vapour permeance of cladding and to reduce solar driven inward vapour drives. The use of spun bonded polyolefin sheathing membrane in lieu of #15 asphalt impregnated felt was found to improved hygrothermal performance in the test walls. The difference observed was concluded to be due to the higher vapour permeance of the spun bonded polyolefin and may not hold for wall assemblies with lower permeance sheathings (e. g. oriented strand board and foam plastic). Walls clad with vinyl siding dried faster than those clad with brick veneer. It was concluded that the vinyl siding is a well ventilated cladding system.

Control of moisture and heat flow through building enclosure assemblies is a critical component of overall building performance. This thesis shows that significant drying of moisture in wall assemblies is possible and that ventilation of cladding significantly increases the rate of drying in some assemblies without having detrimental impact on the enclosures thermal performance. A review found that thermal and moisture buoyancy, wind pressure gradients and mechanical equipment drive ventilation airflow. This ventilation flow can theoretically increase the effective water vapour permeance and thermal conductivity. Ventilation has the potential to increase outward drying through relatively impermeable claddings at the low flows expected to occur in service. The impact on thermal conductance is much less. A methodology for assessing the complicated airflow resistance characteristics of lap sidings was developed and applied to a representative vinyl siding. Field drying studies showed that the sample tested is well ventilated. Field brick veneer clad wall samples were also tested for system airflow resistance over a range of driving pressures. Theoretical predictions under-estimated the measured flow rate for given steady driving air pressures. Measurements of naturally driven cavity air speeds and smoke pencil testing showed that flow rates were commonly occurring that would in theory significantly affect the hygrothermal performance of the walls. This was confirmed with field drying studies. A field drying study of east-facing test wall with vinyl siding and brick veneer cladding was conducted in Waterloo, Ontario, Canada. Significant amounts of drying and inward moisture redistribution were measured. Wall sheathing dried quickly in hot summer conditions but in some cases significant inward driven moisture flow occurred. In cool and cold weather the wall dried more slowly and much less moisture moved inward. Increased cladding ventilation significantly increased drying rates and reduced internal wall assembly moisture levels. It was concluded that cladding ventilation acts to increase the effective vapour permeance of cladding and to reduce solar driven inward vapour drives. The use of spun bonded polyolefin sheathing membrane in lieu of #15 asphalt impregnated felt was found to improved hygrothermal performance in the test walls. The difference observed was concluded to be due to the higher vapour permeance of the spun bonded polyolefin and may not hold for wall assemblies with lower permeance sheathings (e. g. oriented strand board and foam plastic). Walls clad with vinyl siding dried faster than those clad with brick veneer. It was concluded that the vinyl siding is a well ventilated cladding system.