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Old 03-05-2011, 07:58 PM   #1
gwr
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Drop beam under floor joists


Our home has a partially finished basement which was done by the original owner. The family room is unfinished except for an extensive soffit built (by the previous owner) to cover heating ducts/wires/water and gas lines/etc - see attached photo.
The floor was designed for a 40 psf live load and a 15 psf dead load - using 11.875" TJI series joists. The existing soffit covers and area 8.5' X 18' - and is framed with 2"X3",s supported from the joists.
My concern is that with the added weight of the soffit around the ducts/etc, plus the weight of drywall on the bsmt ceiling, might cause the floor to deflect more than the 40 psf LL/15 psf DL allows for.
I theorized that a 1.75" X 9.5" X 18' LVL beam under and perpendicular to the joists would augment the load on the joists and help increase the stiffness of the floor.
Does anyone out there have experience with this type thing and do you suppose I'm on the right track?
Appreciate any thoughts/advice...
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Drop beam under floor joists-bsmt-ceiling.jpg  
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Old 03-05-2011, 10:05 PM   #2
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Drop beam under floor joists


weigh the wood used,then weigh light gauge metal framing.shouldn't be a problem cause it's spread out and anchored to more than just 1 joist.
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Old 03-06-2011, 09:43 AM   #3
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Drop beam under floor joists


The soffit is lightly framed, and likely adds less than 5 psf to the total load. This is not enough to make a significant difference to the overall feel of your floor. Are you posting this question because you believe the floor is not stiff enough, or is this a theoretical question? If the floor is OK now, I would leave it alone, as adding a major structural beam such as you propose is relatively expensive.
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Old 03-07-2011, 12:41 PM   #4
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Drop beam under floor joists


Thanks guys, for your response..
I felt that although the floor meets code, that by adding a small beam perpendicular would provide some additional stiffness and added support to offset any sag due to load duration, etc.
One question is that if I added a small drop beam, would it change the structural design of the floor (changes in reaction forces, etc.) and would the beam assume some of the load on the joists without subjecting the beam to loads it is not capable of?
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Old 03-07-2011, 11:00 PM   #5
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Drop beam under floor joists


Adding the beam could cause a squeak if you don't nail the joists to it,adding more support to the floor will take the bounce out if you have one.To know if you have a bounce in the floor put a glass of water on the floor and jump up and down.Watch the glass you'll know if you need extra support.
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Old 03-07-2011, 11:41 PM   #6
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Drop beam under floor joists


If you add the LVL, how are you proposing to support it? Adding a beam to cut the span of the I joist will not hurt it as these aren't trusses, but if you hang the LVL off of the I joist then it defeats the propose and does hurt it. If you add some post then you are opening a can of worms as you now have to look at supporting the columns with a footing and it becomes a big project.
If you finish off the soffit with 5/8 gypboard, it does add some weight to the joist but might be ok for the 15psf depending on what is on the floor now. Make sure you add a filler at where the studs are attached to the I joist. Is the soffit close to the center of the joist? If it is closer to the ends of the joist, then you might be safe as critical location is at the midspan.
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Old 03-08-2011, 12:09 AM   #7
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Drop beam under floor joists


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Originally Posted by luckattack View Post
If you add the LVL, how are you proposing to support it? Adding a beam to cut the span of the I joist will not hurt it as these aren't trusses, but if you hang the LVL off of the I joist then it defeats the propose and does hurt it. If you add some post then you are opening a can of worms as you now have to look at supporting the columns with a footing and it becomes a big project.
If you finish off the soffit with 5/8 gypboard, it does add some weight to the joist but might be ok for the 15psf depending on what is on the floor now. Make sure you add a filler at where the studs are attached to the I joist. Is the soffit close to the center of the joist? If it is closer to the ends of the joist, then you might be safe as critical location is at the midspan.
I also concur
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Old 03-09-2011, 01:06 PM   #8
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Drop beam under floor joists


The LVL will not be suspended from the joists. I planned on supporting at both ends with 4X6's, breaking out the floor and pouring a 2'X10" concrete pier to support the mess.
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Old 03-09-2011, 01:09 PM   #9
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Drop beam under floor joists


oops... the soffit covers 18'X9' - bearing wall on one end, proposed beaam on the other
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Old 03-09-2011, 07:40 PM   #10
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Drop beam under floor joists


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oops... the soffit covers 18'X9' - bearing wall on one end, proposed beaam on the other
the previous owner ran out of $$$,so he didn't finish the basement
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