Sensitivity of Low Sloped Roofs Designs to Initial Water and Air Leakage

Liquid water in low sloped roofs almost always causes problems. Roofs are designed only to control the migration of vapor, if at all. Small amounts of water leakage/penetration, may cause mold growth or catastrophic corrosion in current roofs systems. In a recent paper by the authors the effect of exterior surface emissive and absorptive properties was found to have a significant effect on the moisture performance of a roof that had a leak. Depending on the surface characteristics, roof systems can be designed to effectively manage water penetration, but at an energy cost. In the roofs system examined previously, air leakage was not included. In the present study, the authors reinvestigated the effect of water penetration and the influence of air leakage on the hygrothermal performance of a few selected roofs. The drying potential of a groove ventilated roof is examined. The performance concept is based on the fact that warming up of air in the groove increases it's ability to transport moisture to the outside. Solar radiation raises the temperature of air in the grooves and on average, during a sunny summer day 0.5 L of water can be ventilated out of the roof per 1m width of the roof. In this paper, one climatic condition was investigated; a hot and humid Climate representative of Houston, TX. The specific questions that the paper addresses are: What are the vapor and liquid control dynamic involved in the moisture migration of a roof in Houston TX? and how does airflow influence the performance of a roof that is initially wet ? A state-of-the-art numerical model was used to address these issues. Results showed that the drying potential depends on the ventilation rates. The roof system with ventilation grooves dried out faster from the initially wet stage than the roof without the ventilation grooves. The total increase in heat loss of the roof was found to be between 0 - 5 % depending on the thickness of the insulation. The ventilation can cool down the temperature of the roof in the middle of a hot and sunny day thus reducing the heat load to the inside

Integrated Hygrothermal Performance of Building Envelopes and Systems in Hot and Humid Climates

In hot and humid climates the interior and exterior environmental loads that building envelopes must respond to are larger than many other climatic conditions. Moisture-originated failures in low-rise residential buildings have put a significant pressure to change construction codes in North America. Solutions to moisture induced problems may be difficult when several interacting mechanisms of moisture transport are present. A new approach to building envelope durability assessment has been introduced in North America; a moisture engineering approach. This requires system information about the wall systems as constructed along with aging characteristics coupled with advanced modeling that 0 term allow the designer to predict the Iong-term performances of building envelope systems. This permits the comparison and ranking of individual building envelope systems with respect to total hygrothermal performance. Critical information can be obtained by investigating the one to one relationships of a building envelope to interior and exterior environments, however, the total behavior of the actual whole building is not accounted for. This paper goes one step further, by incorporating the individual hygrothermal performances of all walls, roof, floor and mechanical systems. The direct and indirect coupling of the building envelope and indoor environment with HVAC system are included in the analysis. The full house hygrothermal performance of an aerated concrete wall system are examined for a hot and humid climate. The hour by hour drying potential of each system was then numerically analyzed using weather conditions of Miami (hot and humid climate). The results clearly demonstrate the limited drying potential for the wall system in that climate. Furthermore, the selected exterior thermal insulation strategies and interior vapor control strategies in this study clearly show the critical behavior of the full house with respect to drying initial construction moisture. The results show the importance of the total hygrothermal behavior of the whole house to the coupling between the various envelope parts, interior and exterior environments and HVAC system. From these results moisture control strategies are identified for the whole house hygrothermal performance

Impact of Air Leakage on the Thermal and Moisture Performance of the Building Envelope

The air tightness of building envelopes systems is critical to the performance of a building. Uncontrolled airflow movements can cause moisture-induced damage by transporting large amounts of moisture, and may also impact occupant health and safety, sound control, fire control and energy efficiency. Building envelopes are often designed to control airflow by providing a resistance to the bulk flow. Implementation of air barrier systems to restrict airflow is commonly used to reduce the quantity of airflow movement between the exterior and interior environments through the wall. This paper presents a preliminary assessment of the influence of airflow on the moisture performance of a residential building envelope system. The combined heat, air and moisture (hygrothermal) transport in a selected wall is numerically investigated. Vapor diffusion, liquid transport and temperature dependent sorption isotherms are included in the investigation

Effect of air leakage on the hygrothermal performance of a high-rise building envelope wall system

Peer reviewed: NoNRC publication: Ye

Overview of hygrothermal modeling

Peer reviewed: NoNRC publication: Ye

State of the art hygrothermal modeling

Peer reviewed: NoNRC publication: Ye

The effect of waterproof coating on hygrothermal performance of a high rise wall structure

Peer reviewed: NoNRC publication: Ye

Porous media transport in building systems

Peer reviewed: YesNRC publication: Ye

Boundary element analysis of two-dimensional uncoupled quasistatic hygrothermoelasticity by DRM

Peer reviewed: YesNRC publication: Ye