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Old 03-08-2011, 12:40 PM   #1
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Weird beam question


I've got this strange situation when I need to remove two parts of the foundation on the corner of my ranch. I can't put posts inside to hold the floor up because I need to drive under there with a bobcat. So my best case of action is to run a beam a few inches away from the foundation I'm removing.

Please review the attached diagram. I'm thinking for the 18' span, 4 2x10's bolted together would temporarily hold the floor joists/wall/roof while we're excavating and redoing the foundation.

Remember, I can't just put posts inside so the span must be a clean 18 feet or so. We will literally be working UNDER that beam.

We are removing the part of the foundation that is in RED.

-- Joe
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Last edited by anesthes; 03-08-2011 at 12:48 PM.
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Old 03-08-2011, 12:45 PM   #2
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Weird beam question


You could easily let the temporary support beam sit back 2' from the edge of the house - to get you more room.

What are you posting down to on each side of the beam?

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Old 03-08-2011, 12:53 PM   #3
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Originally Posted by CookeCarpentry View Post
You could easily let the temporary support beam sit back 2' from the edge of the house - to get you more room.

What are you posting down to on each side of the beam?
We're actually driving the bobcat in from the narrow side so it's best if the beam is close to the foundation being replaced on the long side.

On the inside, It's a crawl space that far back and will sit on a small footing on the soil. On the outside it will probably sit on cribbed 6x6s.

-- Joe
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Old 03-08-2011, 01:00 PM   #4
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Weird beam question


Got it, thanks.

4 2x10s should work. If you are worried, use an LVL or PSL, or steel.
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Old 03-08-2011, 01:13 PM   #5
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Originally Posted by CookeCarpentry View Post
Got it, thanks.

4 2x10s should work. If you are worried, use an LVL or PSL, or steel.
I'm not worried, just ignorant. Looking for advice. I would use steel if it's available, but would cost me upwards of $500 to even get one transported to me to borrow for a few hours. Where 4 2x10's would be like $100. I just wanted to make sure 4 2x10's over a 18 or so foot span would hold the floor without a sag or issue for a couple hours or up to a day while the new footing and wall is poured.

Once the new wall was completed, we will drop the house back down on a double PT sill.

-- Joe
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Old 03-08-2011, 05:11 PM   #6
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Weird beam question


If that is the outline of your house and the exterior wall footing is what you are trying to replace, those 4-2x10 may not be adequate. I assume the footing is picking up the floor joist load, exterior wall, and roof load. Be careful.
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Old 03-08-2011, 06:58 PM   #7
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If that is the outline of your house and the exterior wall footing is what you are trying to replace, those 4-2x10 may not be adequate. I assume the footing is picking up the floor joist load, exterior wall, and roof load. Be careful.
That is correct, it is the exterior load bearing wall that holds the floor, wall, and roof. on the corner.

My question was, where i proposed the temporary beam, will 4-2x10's be enough to temporarily hold the load? It's a single floor and the spans are indicated in the diagram.

Thanks!

-- Joe
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Old 03-08-2011, 07:10 PM   #8
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Weird beam question


I might as well be the first to say it here, call a structural engineering company to come out and do some drawings, this would be the only certain way to ensure the safety of yourself and to keep the integrity of the building.

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Old 03-08-2011, 08:26 PM   #9
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I might as well be the first to say it here, call a structural engineering company to come out and do some drawings, this would be the only certain way to ensure the safety of yourself and to keep the integrity of the building.

Mark
I could do that, I just figured someone could cite a the normal loading guideline using #2 lumber. I looked at the table in the IRC 2009 but don't quite understand what it's saying.

Keep in mind, this isn't perm girder with any type of anticipated snow load. This is purely temporary.

-- Joe
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Old 03-08-2011, 09:02 PM   #10
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Originally Posted by anesthes View Post
I could do that, I just figured someone could cite a the normal loading guideline using #2 lumber. I looked at the table in the IRC 2009 but don't quite understand what it's saying.

Keep in mind, this isn't perm girder with any type of anticipated snow load. This is purely temporary.

-- Joe
18' span is beyond any chart that I am familiar with for #2 lumber. A 16' garage header is 4"x12" and it only supports a roof. For a temporary load, I would be comfortable with 2-4"x12". But the truth is that I would give it a try with one 4"x16".
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Old 03-09-2011, 12:55 PM   #11
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Based on the size of the beam we put into my 22 foot ceiling span -- just to straighten up the ceiling, my gut says that your four 2x10s might be vastly undersized.

But without knowing a lot more details no one can say.

According to the span table I have, one 2x10 spanning 17 feet can support around 1000 lbs.

The same span with a similar 2x12 supports 1600 lbs. Those figures are based on an Fb of 1300. "No. 2" is a visual grading system, and I don't know what kind of wood you have, so who knows what the actual Fb of your lumber would be.

So how much does that corner of your house weigh?

If the depth of your joists is 12 feet, and you have 5/8 ply and asphalt shingles, then you'll be supporting about 500 lbs of roofing. You probably have 800 to 1000 lbs of drywall. 300 lbs of 3/4" subfloor and again as much floor if it's wood. An 18 foot wall with 13 studs would have around 200# of 2x4s. Plus the sheathing, siding, rafters, ceiling joists, etc. If your floor joists are 12' 2x10s then they're around 40 lbs each -- another 500 lbs. If your joists are more than 12', then everything is heavier.

So you could easily have more than 4000 lbs for a single story house of typical construction. What does it mean if the beam you build can support 4000 lbs? It meas it will deflect 1/360 when you load it. That's about 1/2 an inch for 18'. If you load it more (or if your lumber's Fb is less than 1300, it will deflect more. (Note that your span is greater than my span table by a foot).

Sounds like it's about time to call an engineer and get a real answer

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