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.
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.
Later this year 2010 this limitation will be removed.
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.
The magnitude of snow load is highly dependent on local weather patterns terrain and latitude.
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.
The live load on a roof is the weight of any temporary objects on the roof.
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.
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.
6 snow loads versus roof live loads.
Live load lr 20 psf dead load top chord.
A roof truss has the loading shown below.
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.
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.
The live load includes everything that can be moved in or out of a.
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.
It will then explain how to enter these loads if a different outcome is desired by the user.
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 term snow load is used in reference to the downward force on a building s roof by the weight of accumulated snow and ice.
