Residential Framing: Counting Rim Joist Toward Header Requirements

[71corvette]

I'm working on the design of a residential structure and am referencing IRC 2015 for design and sizing of joists, rafters, headers, etc.

Currently, I'm sizing headers and I've got two or three locations where I'm falling a bit short of finding a workable solution using dimensional lumber (e.g. the maximum header span is a couple inches shorter than required). One course of action would be to simply size and LVL. However, it occurred to me a simpler approach could be to simply count the rim joist toward the header requirements.

For example, take the following design requirements:

* Required header span = 7'-6"
* Maximum header depth = 10"
* 2x6 wall framing
* Building Width = 28 feet
* Header supports roof, ceiling and one center bearing floor
* Ground Snow Load = 50 PSF

The header table shows a triple 2x10 can safely span 6'-11. This is obviously too short. However, for this project the floor construction for the second story includes a continuous 2x12 rim joist. I'm inclined to prohibit splices in the rim joist within the limits of the window opening and count the rim joist toward the header. To my mind this is conservatively equivalent to a quad 2x10 which can safely span 8'-0" and, therefore, produces an acceptable design.

Have others used this approach before? Am I missing something that makes this approach unacceptable. Looking for a sanity check. Thanks

 

[phamENG]

71corvette, the IRC is a prescriptive code to ensure contractors and non-registered designers can produce a house that will meet the minimum requirements of life safety, etc.. You either use it as its written, or you invoke the accepted engineering practice clause and design per the IBC and the referenced codes using engineering analysis and design.

So if you're trying to use the tables, use the tables and try not to stray beyond them. If you want to take a closer look at the load path, consider the relative stiffness of the various components in the wall, and detail the connections accordingly - go for it. If you do that, then yes - I'd say you could consider them as acting together as they will all have to deflect together in response to gravity loading from above. Just make sure the detailing makes sense.

 

[XR250]

I use it when I need it. I also don't get too excited about headers being slightly over-spanned as the house will never see the design loading. Try calculating the demand and capacities (instead of using the tables) and see if you are still out of bounds.

 

[kmart30]

Yes I would just fine tune the pencil a bit if the tables are slightly out of what is needed for spans. However, specifying a smaller LVL in one or two locations shouldn't bust the construction budget and you can move on with trying to value engineer things that will really make a difference to the bottom line.