Engineering question

[rat4spd]

For our resident enjineers:

I am currently putting up a 20X20 garage/workshop which will have room in attic trusses. The loading is as follows for the trusses:

top chord 30# live/10# dead, Bottom chord 40# live (in the room area)/10# dead.

The question is, I can't seem to find a reference for a header size for an 8' door. Most references seem to say 1 inch per foot of span, but that is for one story garages. My gut would say 2x12's, but I can't verify it. I'd have no problem buying a microlam beam. They run like $4.xx per foot for 11 inch beams, but if 2X12's would work it would be more economical.

Thanks

Dave Ames

EDIT: forgot to mention, this is on the eave side, not gable.

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[John Bridge]

Hi Dave,

I'm certainly not an engineer, but I was a carpentry contractor before I become a tile setter. Header sizes are good through two-story structures, so a double 2x4 header will span three feet in a one or two story building, for example.

Also, I'm not sure of the type of trusses you are referring to, but the "A" frame type trusses that span from outside wall to outside wall are self-supporting and require no structure under them as far as partitions are concerned. We used to simply use a flat 2x4 in doorways to have something to nail sheetrock to.

[rat4spd]

Oh, OK. I had assumed that the header spans usually referenced single story supporting the roof only. In that case, 2X12's should be good. The trusses I'm using are clear span "Room in Attic" A-Frame trusses. They are gonna give me a room 14' wide with 6' headroom. Good thing I'm not 6' tall.

Thanks

[John Bridge]

Yeah, well, what I'm saying is you don't need any headers at all inside the building, only on the exterior supporting walls. :)