On page 2 of the 20x30 1/2 there is a table on the top right that reads: loads at header. I assume this table is used to determine the number of 2x's to use for the headers over doors/windows depending on the door/windows width? Is this correct?
So for the 1st floor, if my french doors are 6ft wide, then i need to use 3 x 2x10's for the header above that door ?
Thanks,
I do not have a copy of the plans to refer to, but the header size and the number of jack studs required to support the header vary, not only with the width of the opening, but also the width of the building, the height (number of floors), whether or not there is a center support beam or only side wall supports, and if the wall is a load bearing wall or a non load bearing wall as well as the local snow load.
Lots of variables.
The Table 502.5(1) [page 138 in the MN version of the IRC2006] is a guide to those sizes.
Yes, the header chart you are referring to is sized for the 10' wide loads of the roof and floor of the 20' wide building and use a 30 psf snow load. You are reading it right for a 1st floor load that carries a roof and floor load.
Checking the MN chart Don mentions they would allow 3 2x8s for 30 psf or under - going to the 3 2x10s for up to 50psf snow load.