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2x10 extensions


jmann's Avatar
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04-07-04, 09:43 AM   #1  
jmann
2x10 extensions

I am in the process of trying to make a large room out of three small ones in my 1940's cape cod. Currently I have two partition walls on level 1, which each hover around 3 feet from basement beam. What I have done so far is to install a new header on floor 1 that is in between both partition walls, and almost directly over the houses main support. The room span is approx 27' and the current ceiling joists are 2x10 16" OC.

The only problem is that one of the partition walls is directly under the joist overlap/seams. Therefore, my joist are about 3' short of the new header. I'd would like to somehow sister or mend the seam without adding another header.

I have been working with my uncle, who's a carpentar, and he says to sister them with 2x8's about 8 feet, and bolt with 1/2" bolts. This sounds good, but will it really work?

Any other advise?

Thank you,
jmann

 
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04-07-04, 08:54 PM   #2  
bungalow jeff
No. You need another header, or framing that can handle the new span sistered onto the existing. Your uncle thinks adding short sections of smaller beams will make the existing framing span further? Youch.

 
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04-08-04, 05:44 AM   #3  
Why not move your new support beam(header) to where the old load bearing wall was? What I mean is, why are you putting a new support beam 3' away from the joist overlap seam?

 
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04-08-04, 07:06 AM   #4  
jmann
Jeff:

well, last night I s/w with a freind who is an architectual engineer and he is looking into the exact solution....its somewhere along the lines of what my uncle said...but with bigger/longer beams to handle the pressure. a new header is idea, but just wont work in this setting

Its not that my uncle said just patch in small sections of 2x8 to extend the joist....he wants me to sister the old ones with minimum 8 foot sections....which I think would work, fundamentally..you dont?

Coops:
The new header is where it is becuase it will be the only thing one on that side of the house. Therefore i wanted to put it directly over the beam in the basement. Currently there are two partition walls...one of which has the overlaps above it. Believe me..if I could have put the new header where the old one was, I would have.....you know its always 10x more difficult for remods, vs. starting over from scratch...

 
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04-08-04, 09:10 PM   #5  
bungalow jeff
jmann,

What your uncle is suggesting is to increase the span length of the framing with a short section of a smaller member. Now, this is done with steel girders, but steel has a much greater bending capacity than timber. By extending the span three feet, the new span may be too long for the existing 2X10's at the center of the span. It is very likely that the bending moment at the end of the 2x10 will be too great for the 2x8 splice. This is why your friend with some actual training is recommending larger and longer members.

Have you considered a 10" engineered header placed up within the depth of the 2X10 framing? Temporarily support the framing, remove the wall, cut the 2x10 ends off, install the engineered header and use joist hangers to resupport the 2x10's on either side. Engineers from the manufacturers usually design these members for you with enough framing and layout info.

 
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04-09-04, 12:57 AM   #6  
There can be some pretty creative (and safe) ways to deal with what (I think) you are doing.

The possibilities are dictated by the potential load-bearing paths to ground.

I think your situation could use a few hours of a structural engineer's time. If not that, find a building inspector who consults. I have this nagging suspicion you have caused problems with the replacement of two walls with one header.

Are you concerned that the header will sit under the joists? It doesn't have to be that way. It may need to be deeper than the joists that hang from it, but sometimes compromises need to be made.

 
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04-09-04, 08:21 AM   #7  
I do not know many engineers

that would be willing to seal a drawing that includes the scabbing of a 2 x 8 to a 2 x 10 to increase the length.
Basically there are two main flaws in this design technique.
(1) if a scab is placed to only side of the joist you will create an excentric loading condition that will cause a twisting motion at the connection of the two members that cant really be designed for properly.

(2) because of the difference in depths of the material it is almost impossible to predict the stress transfer at the intersecting locations of the members. The net section on this type of beam is almost impossible to calculate. The only way that most engineers would seal something like this is if the member in question was adequately sized as the smaller of the two members (i.e. the joist in question really worked as a 2 x 8 instead of a 2 x 10) and then you must find some means of preventing rotation about the axis of the insersecting members since the loading is now excentric instead of concentric.

 
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04-13-04, 12:19 PM   #8  
The partition wall you are talking about the one with the joist seems over it is your original bearing wall. The Ideal method would have been to cut the joists at the seam leaving a 3 inch gap between the two slide in the header and the attach joist hangers to support the joists. The bearing wall was designed there for a reason. Any type of sistering will create a week point that you will be sure to confront later be it with cracks in the drywall tape joints or a ceiling that waves back to you. Good luck wit that ever you do.

 
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04-13-04, 04:48 PM   #9  
Homer has stated the situation accurately. Bravo.

 
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