Rhode Island Flat Roof Snow Load by Municipality

Roof snow load and ground snow load are different quantities, and Rhode Island lists both. The Rhode Island Snow Load, Wind Speed and Frost Depth Table carries a Flat Roof Snow Load column in pounds per square foot next to the Ground Snow Load column, for all 39 municipalities. That is a meaningful convenience: in states that publish only a ground snow load, the roof figure has to be calculated from it using the code's exposure, thermal and slope factors. Publishing the flat roof value directly removes a step and removes the disagreements that come with it. The two columns are not interchangeable, and a design that applies the ground snow load figure where the flat roof value belongs, or the reverse, is using the wrong number, which is the most common confusion in this part of the code.

Enforced at plan review. Structural drawings must show the roof designed to the flat roof value listed for that municipality, with sloped roofs adjusted from it under the normal code provisions. Substituting the ground snow load figure for the flat roof figure, or vice versa, is the error to watch for, and it is caught by comparing the drawings against the correct column of the state table.