Author Topic: Floor Joist Questions  (Read 462 times)

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Offline Rys

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Floor Joist Questions
« on: May 02, 2018, 06:00:25 AM »
 After a great deal of going back and forth we've decided to go with a 24x40 w/loft. I just didn't like how tight things would be with my staircase if I went 20' wide. The cabin will be built over a full basement. I would love to have an open basement room mirroring the main floor living room.
 My question is if I need additional floor support under my "open" living room. It will be approximately 23'w X 15'. I hope to be able to have my beam that will be holding the floor joists supported at the staircase post running up from the basement.  In other words the floor joists will go from the middle beam over to the foundation walls on three sides. Will this work?

Offline Don_P

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Re: Floor Joist Questions
« Reply #1 on: May 03, 2018, 02:21:10 AM »
This is gonna take a picture for me, maybe someone else is visualizing it.

Offline Rys

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Re: Floor Joist Questions
« Reply #2 on: May 03, 2018, 05:30:52 AM »
I40237900001

Offline Rys

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Re: Floor Joist Questions
« Reply #3 on: May 03, 2018, 05:32:06 AM »
Back to the drawing board. I'm determined to get this picture business figured out!    d*

Offline Rys

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Offline Rys

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Re: Floor Joist Questions
« Reply #5 on: May 03, 2018, 06:53:46 AM »
Got it!
The dark blue lines along the edge are the block basement walls. The single dark line down the middle is the beam that the floor joists (16" oc) will hang from. It will rest on the uprights on either side of the stairs. Their other end will be supported by the block walls.
The area above will be the same dimensions.
 We plan on using raised heel parallel chord trusses for a cathedral feel to the main room.
 Any input?advice greatly appreciated!
TIA!

Offline Don_P

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Re: Floor Joist Questions
« Reply #6 on: May 03, 2018, 02:59:29 PM »
Good deal  :)

Just some thoughts, you can span 24' without a center girder with open web floor trusses, I'd imagine some size of I joist would also... but it doesn't make for a great floor, vibration, and would be deep

Dimensional lumber joists spanning 12' can be as small as 2x8, nothing wrong with 2x12.

Lets check out the size of LVL needed for a 15' girder supporting 12' of tributary width... the foundation walls support 6'x15' on each side. 180 sf x 50 psf= 9000 lbs total load on the girder.
 http://www.timbertoolbox.com/Calcs/beamcalc.htm
Inputs;
9000
180
5.25
11.875
2800
2
280

A triple 11 7/8" LVL would work, the supplier can confirm that. A 2x12 is 11 1/4" deep so there is a slight bump in the ceiling below there.

Back out the 5.25 and plug in 3.5, back out the 11.875 and input 14 and notice there is less deflection. If you can handle the deeper beam in the ceiling below that is a cheaper and stiffer alternative, a 2 ply 14" deep LVL.

Offline Rys

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Re: Floor Joist Questions
« Reply #7 on: May 03, 2018, 04:04:42 PM »
Thanks Don!

 

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