Snow Infiltration Tests and Pressure and Flow Rate Measurements on Ridge Vent Configurations

The present study addresses the performance of roof ridge vents in regard to the possible entry of snow into the attic space under strong wind conditions. A total of 11 vent configurations made available by Air Vent Inc. were tested for snow infiltration. Additionally, attic pressures and flow rates were measured for 13 ridge vent arrangements, including the 11 tested for snow infiltration. For reasons of expense, time, and ease of execution, wind tunnel models of snow blowing and drifting have been used for many years in design and in specific problem solutions. A fairly large number of modelling materials have been employed, e.g. sawdust, mica, gypsum, peat, sand, borax, magnesium carbonate, glass beads, activated clay, expanded polysterene, wheat bran, and semolina. (A recent study of snow loads on the Hubert Humphrey Metrodome in Minneapolis was carried out for example using glass beads with a diameter of 0.1 mm, at a scale of 1:384.) In the present study, however, to simulate field conditions as closely as possible, actual natural dry snow was used. The tests were conducted during winter months using the open circuit mode of operation of the St. Anthony Falls Hydraulic Laboratory. The results of the study offer a comparison of the effectiveness of various ridge vent designs, valid of course under the conditions under which the tests were carried out, as described in detail in this report. The tests have been carried out to date at a wind approach angle of 0 degrees (wind direction perpendicular to the roof ridge ). The model has been constructed in three pieces (a central piece and two angle pieces) so that, by omitting the two angle pieces, it can be fitted in the tunnel in a rotated 45 degree position for additional testing with 45 degree approach winds. This testing, originally planned for the winter of 1995, had to be postponed until next winter due to the surprisingly mild 1995 winter weather conditions in Minneapolis.