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Kudos to kcoyner,
Last year, 2 hours before meeting with a building inspector, I posted a query about when code (CABO) required double trimmers. New Building inspector in a small town had decided that “code” required double trimmers on any opening over 4′. Scoured my code book, could find nothing and asked for rules of thumb, anything. Knew that my rule of thumb, learned on a rock and roll tract framing crew could be cheesy at best. Had 3 good answers before I left, none definative but I liked kcoyners conservative approach best, took my manual with me as inspector said he could show it to me. He couldnt. Gave him kcoyners rule of thumb and told him where I got it. Another builder just showed me his “approved” set of plans for a 2 story today and red inked in was” double trimmers on all headers 4′ or over 1st story, 5′ or over 2nd story.
JonC
Replies
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He has been absent lately -- as had Mr. Samson. Could we invite them back?
*In the case of A.J. Samson, you might consider letting sleeping **** lie. :}
*...do you mean two trimmers on each side? - jb
*yepJonC
*That seems like overkill on a 4' (even 6') opening to me. I'm NOT saying it's wrong, just seems a bit over done. - jb
*I always use doubles on 6' and over, but I'd be interested in what kcoyner's "rule of thumb" was...Dan
*Jim and Dan,As I recall, the rule of thumb I got from him was to double on any openings over 5' single story and 4' 1st floor 2 story. It does seem very conservative to me. The other responses I got were from UBC guys and they thought it was 6' or 8' single story. At the time I was pretty much framed up and 2 hrs from meeting with the little maniac who had decided that CABO required me to have double trimmers on any opening 4' or over. I had 4' windows all through this house. Took my manual as he said he could show it to me (me being too dumb to find it myself and his job being to educate stupid builders) Told him what kind of responses I'd gotten to my query and presented kcoyners rule of thumb as the most conservative approach I'd come across.(and this particular house met kcoyner's criteria)Well, he spent an hour on the site trying to find it in my manual, decided I must be missing a new update and assured me he had it highlighted in his manual in at the office and would bring me a copy. Two hours later he comes by says he cant find anything in code about when to go to double trimmers but by golly they'll be red penning it in during plan inspections from now on and I'm OK.I'm sure some folks on this board would have fits with it due to the thermal bridging but in my reletively mild climate I can live with this ROT until I find something more definative to replace it with. Wont even tell you the rule of thumb I learned in the tracts 20+ yrs ago although I can say that I've ever seen a header fail for lack of bearing on a single trimmer. Seen some interesting failures due to no trimmers in old houses (header just spiked through the king, no header etc.)JonC
*Perhaps you can infer from CABO Table 602.3d "Maximum Stud Spacing" when to double the trimmers. My idea is that by cutting an opening and installing a header, you're just redistributing the overhead load to studs on the edges of the span, which you now call "trimmers". If building a one-story bldg, the table says the max stud spacing is 24". Imagine spacing the usual 2 trimmers like regular studs: you'd span 4' from the first king plus 2' more to the next king (3 stud-to-stud spaces) -- 6' total. Beyond that the studs would be overloaded unless doubled. Moreover, because 16" o.c. is the max for 2 stories, 3*16"=48" (4') would be the double trimmer threshold...Does that work? It does justify the slightly more conservative rule of thumb.
*Hello all,I,m not missing, just very busy this year, but still find time to drop by once in a while.Let me first say that my intent here is not to make code policy. It is great however, how all of our ideas, techniques and methods put togather, make this board such a respected site in the construction industry. My methods are usually a bit on the conservative side, but I feel it is better to overbuild than underbuild and have problems down the road. andrew d is correct in noting the stud spacing code as a source for my recommendation. It's how I learned to frame openings from good carpenters in the beginning of my career.