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.
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.
Live load lr 20 psf dead load top chord.
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.
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.
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.
Snow unlike live load is considered to everywhere present at a given time.
The live load on a roof is the weight of any temporary objects on the roof.
If you live in the us our snow load calculator compares the total weight on your roof with the permissible load calculated according to the standards issued by the american society of civil engineers regarding the minimum design loads for buildings and other structures asce7 16.
The magnitude of snow load is highly dependent on local weather patterns terrain and latitude.
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.
6 snow loads versus roof live loads.
Lr is adjusted based upon the area the roof member supports and can be as low as 12 psf in cases where a roof member supports over 600 square feet of.
Currently it is not possible to consider both types of loading simultaneously.
A roof truss has the loading shown below.
Later this year 2010 this limitation will be removed.
Or the 25 psf snow load could be entered as a roof snow load with the unbalanced snow loading option turned off.
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.
Snow loads occur in colder climates and are of varying duration.
Versatube structures are pre engineered to handle more than the snow load they also have to ensure the structure will meet the live load requirements.
