Abstract
Roof overhangs are used traditionally to reduce the amount of rainwater that is deposited on building facades by wind. This thesis investigates the effects of overhangs on the wind-driven rain (WDR) wetting of facades, which have not been studied in detail before, using CFD-based numerical simulation. The commercial CFD package ANSYS FLUENT is used to solve the multiphase flow of wind and rain around buildings. A MATLAB code is developed to post-process the CFD results and calculate the WDR parameters. The numerical scheme is validated by comparison to previously published results and field measurements. Roof overhangs are shown to be effective in protecting facades from WDR, especially at upper parts. This protection is highly dependent upon the overhang size, wind speed, wind direction and the building geometry, but is slightly affected by the rainfall intensity. Physical explanations are presented for the observations and a new global measure of the effectiveness of overhangs is introduced.
Highlights
It was a rash of rainwater leaks in multi-unit residential buildings in Southern British Columbia during the early 90s that drew attention to the failures caused by moisture in buildings in Canada
The motivation behind this study has been the numerous cases of envelope failure in the coastal climate of British Columbia, Canada due to moisture loads and mainly wind-driven rain (WDR)
Their influence on WDR and how their performance is affected by different factors, such as size, wind speed and rainfall intensity, are not known to the designer
Summary
It was a rash of rainwater leaks in multi-unit residential buildings in Southern British Columbia during the early 90s that drew attention to the failures caused by moisture in buildings in Canada. In 1996, a field survey conducted by the Building Envelope Research Consortium (BERC) confirmed that, rather than moisture from construction or condensation due to air leakage, rain penetration was the main source of moisture leading to building envelope failures [1]. Morris [3] has mentioned underestimation of wind-driven rain to be one of the causes of the problems in building envelopes, in the regions with damp coastal weather. It is well established that among different sources of moisture deposition on buildings, wind-driven rain is the most critical, especially in climates like the costal climate of British Columbia, Canada
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