What beam size should I use for 20' room span


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Old 10-17-08, 01:50 PM
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What beam size should I use for 20' room span

Hi

My home is 20' X 45'
The lower level (basement) is sitting on a crawl space.
The walls of the upper level are not lined up with the walls of the lower level so I cannot use them as bearing walls.
I am left with 20' span between the outside walls.
Will 2" x 12" x 24' on 16" center be enough to bear another level (3rd level) and a roof of course.

Thanks in advance
 
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Old 10-18-08, 06:25 PM
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You're better off checking with an architect. You won't get an answer here because no one wants to take a chance. I've done a few as a helper and we used a triple 2x12 but don't take that as gospel. You can always go with a steel I beam as well.
 
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Old 10-20-08, 09:22 AM
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the thread title says "beam" and your post says 16" centers between outside walls? so which is it, are you sizing floor joists or a beam that is intended to support 20' worth of joists and roof?
 

Last edited by OhioDraft; 10-20-08 at 09:23 AM. Reason: confusing mis-spell
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Old 10-21-08, 05:42 AM
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What beam size should I use for a 20' room span

Originally Posted by OhioDraft
the thread title says "beam" and your post says 16" centers between outside walls? so which is it, are you sizing floor joists or a beam that is intended to support 20' worth of joists and roof?
Hi there. Thanks for taking the time and replying.

I will try to clarify; the dimensions of the house is 20' X 45'
The house has a buried crawl space, above it there is a half buried basement and another level on top of it. So if you look at the house from the front you see one level and if you look at the house from the back you see 2 floors. The bearing walls are not lined up and I cannot use them to support another level (3rd one). So after I take down the roof I would like know what beams should I use to support the 3rd floor. I mean the beams that will sit on top of the outside walls side to side and act as a floor for the 3rd level. They will support the 3rd floor and the roof on top of it.
Hope it is clear now. Thanks.
 
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Old 10-21-08, 06:10 AM
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still blurry, so i'll outline my opinions for each of what situations you could be describing to eliminate some back and forth here:

ok first, you say your bearing walls do not line up. do you mean 1)the exterior walls or 2) are there interior brg. walls that do not align? if the exterior walls do not align, to me that means there are either some cantilevers, or for some strange reason the top floor walls are recessed inside of the bottom floor walls.

1) if there are cantilevers, typically the wall and roof load from above rest on the floor joists and are carried down through the bottom floor walls to the foundation. that is for a small cantilever, for a larger one there may be posts and footings to help hold it. In either case, adding an additional floor on top of these systems will almost certainly require some additional reinforcing of the existing structural elements. the same holds true if again, for some reason, the top floor exterior walls are recessed. 2 words, structural engineer.

2) OR if the top&bottom floor exterior walls ARE in alignment, then adding another floor is a lot more feasible but again, will require a pro to verify that the existing foundation can carry the extra weight. also, if this is the scenario, the assumed interior bearing walls are not that big of a factor since you could just make that 20' span with some I-joists. having said that, do not pass off the integrity of your homes structure, the engineer is necessary in either of the 2 cases; you wont hear me say that a lot and i work for one (and will be one upon passing examination) .
 
 

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