As you may already be aware, there are restrictions in International Building Code that prohibit the use of gravel on roof tops if wind speeds are too high in your area, or if the building is too tall. But do you know when these restrictions apply? Guidelines have been imposed that prohibit the use of gravel and stone on any building where the mean roof height exceeds that permitted by Table 1504.8 of the 2009 and the new 2012 International Building Code. The use of gravel is also prohibited in hurricane-prone regions.
A hurricane-prone region is defined as the U.S. Atlantic Ocean and Gulf of Mexico coasts where basic wind speeds exceed 90 mph, or in Hawaii, Puerto Rico, Guam, Virgin Islands and American Samoa, according to the 2009 IBC. However, you will notice that the 2012 IBC shows the hurricane prone-defining wind speed as 115 mph instead of 90 mph. Please note that this is basically the same wind speed. Wind speeds have increased in the new 2012 IBC. Wind speeds that were 90 mph in 2009, are now referenced as 115 mph in 2012. What this boils down to is that the same gravel restrictions apply to the 2009 and the 2012 IBC.
The main reason that these restrictions have been imposed is to reduce the damage to other buildings due to the breakage of glass, windows or other glazing. Field assessments have shown that gravel or stone blown off of roofs due to high wind speeds have broken windows in surrounding buildings. Once these windows have been broken, the wind pressures can cause high internal building pressures that can result in structural damage to interior walls and to the walls and roof surfaces that are subjected to negative external wind uplift pressures.
Please note that this are the restrictions set forth by the International Building Code. Your local code body may reference these same restrictions, or they may provide allowances in certain circumstances. We all know that flood and gravel surface, mod bit roofs are outstanding high performance systems. So before you dismiss this surfacing option due to height or location restriction, be sure to check with your local code official to see if gravel is permitted on your particular roof.