Moving Header Supports
This is a long post, but I'm trying to include as much relevant info as possible for your evaluation.
My questions regard a lanai (a covered outdoor room surrounded by the walls of the house on 3 sides and screened on the other side for you non-Floridians http://forum.doityourself.com/images/smilies/smile.gif ). My problem centers on the 27' screened wall of the lanai.
The lanai is part of an addition done 10-15 years ago. I pulled off the soffit vent and can see that the roof is made up of 2x6 joists, one end of which rests on the original poured cement wall of the house and the other end of which rests on a top plate (2 flat 2x4s) above a double 2x10 header. The lanai itself is 12' deep by 27' long and everything rests on a poured cement slab.
The screen wall header is made in three sections - two 10' sections and one 7' section. Each header section has a king stud at each end that extends all the way up to the top plate, a jack stud that supports each end of the 2x10s and three 2x4s sandwiched together serving as a post in the middle of each header. It's almost as if they framed up three header walls and joined them together. Making sense so far?
I am sprucing up the lanai and want to "adjust" these supports to create larger, evenly spaced openings. There are currently 5 posts along the 27' span including the "king/jack combo" posts and the center supports which create six 5'-3.5' openings
My plan is to insert two 4x4 posts which would leave three 9' openings along the 27' span. I would insert the new posts up to the bottom of the 2x10s, then knock out the old posts, using a reciprocating saw to cut the tops of the king studs flush with the bottom of the header.
Doing this would place the two new posts approximately 1' away from the current king/jack stud supports at the joint between each header section. I also considered fastening a metal plate over the joint between each header section to "tie them together". (I should mention that I can't access the surface of the outer 2x10, so this metal plate would be attached only to the inside 2x10. I thought to then use bolts with a countersunk head to tie the inside and outside 2x10s together near the joints) Still with me? http://www.diychatroom.com/images/smilies/redface.gif
I'm effectively moving each of the two main supports 1' and eliminating the center supports.
I'm in central Florida, so obviously no snow loads to contend with. Does this plan sound doable? Would three nine foot openings along a 27' span be an invitation to a sagging header? Would anyone recommend a different way of supporting the joints between the header sections? Does it sound like a roof collapse is in my immediate future? http://www.diychatroom.com/images/smilies/eek.gif
Any input or suggestions from some of you pros out there would be greatly appreciated.
Any chance you could replace the header with a laminated product, like a Paralam beam?
Can you possibly take some photos and upload them?
Your post was very descriptive and your plan is structurally sound. Although the centre header would now be supported solely by by the steel plate and the bolts, there would be no cause for concern about sagging or a failure. I would suggest a plate 1/4" thick and 12" long and have the bolts as far away from the ends of the header as possible to avoid possible splitting. One thing I'm not quite clear on though, is the fact that you cant access the outer face of the header so I'm assuming that you intend to use lag bolts screwed in from the matal plate side. I've never seen countersunk head lag bolts. If you are in fact using lag bolts (min. four 5/8" dia.) drill pilot holes through the header a little smaller than the root diameter of the thread, again, to avoid the risk of splitting. I'd be interested if you post back on those bolts
I'd talk to someone like an engineer for this. The idea of removing all support from the centre beam/header and relying on tying it to the adjacent ones with steel plate and lags doesn't sit well with me. At any of these joints you're creating you have only two lags holding one end of this beam. I really prefer the idea of replacing the beam in the middle with a 9' and putting the ends on your new posts, this is not that much more work or material and is a lot more structurally sound IMO. This way you remove the sawn-off ends of the king studs that are otherwise going to be buried in the steel plate joint and it allows you to sister another 2x10 across the new butt joints to create a real beam.
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