Building height plays a large role in calculating wind pressures on a structure. Wind will affect a building and its components differently if it can travel overtop of the structure, or if it must go around the sides at it blows past. The ASCE 7-16 code uses a structure’s Mean Roof Height as a main factor in calculating the positive and negative wind pressures acting against that structure.
Per ASCE 7-16, the Mean Roof Height (MRH) is defined differently for “flat roof” structures (Roof angles less than or equal to 10 degrees, or 2:12 slope) and sloped roof structures.
For flat roof structures, the MRH is permitted to be taken at the highest roof eave height. This considers both the highest roof eave, as well as the lowest elevation at the structure’s base. This measurement is applicable for structures with multiple eaves, gables or sloped roofs, or with structural parapet walls – if the rood angle is not steep, the MRH will be calculated to the highest point.
For roofs with slopes or gables greater than 10 degrees, the code allows a reduction in the MRH to account for the wind being able to pass more smoothly overtop of the structure. Instead of using the highest point on the roof, for sloped roofs, the MRH may be calculated as the average between the maximum roof height and the eave height.
If you need to calculate wind pressures acting on windows, doors, or other building components, you may choose to use our pre-calculated win d charts or our online calculator. Both tools require information about your project, including the MRH, which plays a large role in pressure calculation. Generally, the larger the MRH, the higher the pressures on the structure will be.
Last Update: July 9, 2024
