| Canadian Housing Information Center (CHIC), Technical Series 96-213
An exploratory study has been conducted at the Boundary Layer Wind Tunnel Laboratory of the University of Western Ontario to investigate the climatic relationships between rain and wind.
Canada Mortgage and Housing Corporation, through their interest in wind, rain and the building envelope, initiated this project. The scope of the study was an outcome of discussions with Jacques Rousseau of CMHC and Alan Davenport and David Surry of the BLWTL. The primary objective was to examine the relationship between wind and rainfall rate. A secondary objective was to explore the applicability of the existing Driving Rain Wind Pressures (DRWP), derived by Welsh, Skinner and Morris (1989), to the problems of the building envelope.
The data base used in this exploratory study consisted of 10-year records (1980-1989) of 1-minute average wind speeds and directions recorded every hour along with the corresponding hourly rainfall for five stations across Canada. Only the months of April to September were examined to ensure the availability of the rainfall data from automatic rain gauges. These data were sorted into seven categories reflecting different rainfall intensities. The wind speed statistic (i.e. histograms, averages, standard deviations and 10-year extremes) were calculated for each category and wind roses were constructed using the wind directions for all hours and for wet hours only.
It was found that the preferred directions of strong winds accompanying rain are significantly different than those associated with all conditions. This may provide useful information to sophisticated designers of building envelope systems.
Results also indicate that mean wind speeds are consistently higher during rainy hours than during all hours (in some cases the mean speeds increase consistently with rainfall rate); however, 10-year extreme wind speeds were found to be consistently smaller for wet hours than for all hours. Much of this reduction of extreme speeds for wet hours is attributed to the reduced number for opportunities for the extremes to occur - i.e. rainy hours only make up a small percentage of the total time.
The limited data base examined indicates that a simpler definition of the DRWP as simply a fraction of the National Building Code of Canada's ten year pressure may be justified, considering numerous other uncertainties involved in designing building envelopes for water penetration.
Suggestions are made for improving the data base and the analysis methods to best describe wind conditions during rain. This work should be continued using a much broader data base than was possible to use in this exploratory study.
Project Manager: Project Manager: Jacques Rousseau | 
