I am getting ready to frame my first wall and I am thinking I can omit the header above the 5 foot wide window due to the fact that I have a 4x12 beam underneath the top plate (the beam is there to cantilever out over the gable end to support a porch roof). The top of the window would be about 2 feet below the bottom of this 4x12 beam. My concern is that my approximately 2 foot cripple studs above my window rough opening would transfer load from the header above. However, load usually goes to stiffness, so as soon as the window rough opening started sagging the load would go back up and around the window?
The loads are significant and my original header was a 4x10 for this particular window. If I can omit the 4x10 header I will gain quite a bit of room for insulation and save a little money.
I guess the questions are 1) will this work 2) should I omit the cripple studs to eliminate the possibility of loads being transferred from the header above?
I, for one, would find this question easier to understand if a drawing/picture was supplied. Am I correct to assume this is in a side wall with rafter loads being supported?
This is a load bearing side wall. I read up a little and it seems like it is actually pretty common to cripple down to the rough opening by framing the header at the top plate. I don't see why my big old beam for a top plate cannot function as a header. I would cripple down to the rough opening of the window.
(https://imgur.com/qjofS61)
(https://i.imgur.com/qjofS61.jpg)
(http://[imgur](https://i.imgur.com/qjofS61.jpg))
As long as that beam can span the 5 feet I would think it's fine. You could check it with Don P's calculator. The only concern would be if you are in a heavy snow load area..
You also should keep the cripple studs so you can tie the sheathing in with everything.
Personally I always try to err on the side of beefiness....I would probably go ahead with the header, and wedge the cripples in tight between that and the beam....cantilever will always be trying to make the beam pivot, extra beef will help keep things from getting hinky over time....
If the beam can support the loads just fine at that span, then structurally you just have a window opening that is 2' taller than needed. Since you still need to frame the openening with something, I would go ahead and frame up a 2x4 header just above the window. That won't take much more lumber than just boxing in the window and should give you some peace of mind.
Deflection is the kicker but easily checked, that is a uniformly loaded beam over post I assume, there is a calc in the toolbox for that situation. Allow adequate headspace over the window for the deflection of that area. IIRC in the wall chapter of the IRC there is mention that a header is required if there is greater than 2' of wall above the opening.
Thank you for the comments. The beam will work as the header, but I really like idea of adding an additional small 2x4 header at the top of the window rough opening. This will provide some stiffness to the rough opening and still allow more insulation than the 4x10 header I originally was going to use. Funny, none of my construction books showed the headers "being slammed" to the top plate, but there doesn't seem to be anything wrong with that approach.
Just more header stuff to ponder that is sort of related. One thing people forget about is that a long spanning beam needs lateral support to keep the top loaded edge from buckling out of plane. A classic header failure problem that is brought up in class is a dropped garage door header. Think about assay a 10' tall garage ceiling with an 8' tall door that is 16' wide. The header supporting the roof or a floor and roof. If the header is dropped to the 8' height with a section of cripple wall above it to the top plate, when heavily loaded the header and wall above will bow outwards under load. If the header is put up under the plate with the 2' of wall hanging below it, the ceiling provides lateral restraint so that when load is applied the beam cannot move sideways. Whenever you are hanging that section of wall under the beam do bear in mind it is hanging from the header, bear this in mind as you frame and sheath and tie that hanging wall up to the header sufficiently. that is part of why they limit that unheadered wall section to 2'.
Don would that be an engineering class or something for builders? Just curious. Interesting info.
I picked that up in an engineering short course at Virginia Tech, a number of land grant universities hold those type of continuing education classes. Usually they are full of engineers, architects, inspectors and carpenters but are open to all. That particular example is also online, I'll try to dig up that article, running late right now d*
Here it is;
https://i-joist.org/wp-content/uploads/2018/05/WIJMA-Dropped-Header-Design-Guide-11-7-07.pdf
I went to a workshop up in WV this week at the Wood Education Resource Center, neat facility and a good class. The wood extension agent from NC stopped by our job yesterday on his way back home, we were milling some 24' 8x12 beams and making charcoal from scraps which he was interested in. The interesting discovery is he has a grant to make some residential cross laminated timber panels, the focus thus far has been large commercial expensive facility, heavy panels, he wants to do small residential stuff in affordable facilities... this should be interesting.
Thanks Don.
Hadn't heard of cross laminated timber either. Seems like you could do some creative stuff with that.