Roof Live Load Vs Roof Snow Load

The term snow load is used in reference to the downward force on a building s roof by the weight of accumulated snow and ice.

Roof live load vs roof snow load. Where snow isn t a problem the live load can come from people working on the roof and any equipment they take on to the. Within the criteria member loads menu in ram manager there is an option to consider either roof live loads or snow loads during the gravity analysis of the structure. This article will explain how special loads or girder loads are calculated when both roof live load and snow load are turned on in truss loading. Or the 25 psf snow load could be entered as a roof snow load with the unbalanced snow loading option turned off.

Currently it is not possible to consider both types of loading simultaneously. It will then explain how to enter these loads if a different outcome is desired by the user. A roof truss has the loading shown below. The live load on a roof is the weight of any temporary objects on the roof.

Snow unlike live load is considered to everywhere present at a given time. The magnitude of snow load is highly dependent on local weather patterns terrain and latitude. Live load lr 20 psf dead load top chord. In my region on cape cod we have a ground snow load design of 25 psf which is a greater design load than the live load 12 psf to 20 psf over an entire roof system.

6 snow loads versus roof live loads. The live load includes everything that can be moved in or out of a. The bottom line is that the irc requires you to design the roof structure to the greater roof load and in my region that s the ground snow load. There is also a minimum roof live load known as lr of 20 psf defined by code psf pounds per square foot which accounts for weights such as construction loads when pg values are very low.

Later this year 2010 this limitation will be removed. Snow loads occur in colder climates and are of varying duration. If unbalanced snow loading isn t required or specified the truss designer may enter the 25 psf snow load as a top chord live load tcll set the load duration factor to 1 15 for snow and turn snow loading off completely.