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StructuralEng
StructuralEng, Consultant
Category: Structural Engineering
Satisfied Customers: 6752
Experience:  Structural Engineer
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My question is concerning replacement of a somewhat load

Customer Question

my question is concerning replacement of a somewhat load bearing wall, with a beam in the attic on top of the joists
The house is a pretty plain Ranch 1950s, 1500 sq feet, stick built, with a crawl space below the first floor.
The wall i'm replacing is in the center of the house running perpendicular to the joists in the attic and they overlap on to of this wall. The joist are 16 inches apart and are 2x8. I will be removing 12 feet of this wall....The beam will reside on top of the joists, with one end on the outside wall and the other on a 4x4 and 2- 2x4s ....It is very well supported in the crawl space under this support...
It is a closed couple roof with a Ridge board the length on the house, but there are several braces double 2x4s nailed to the top plate of the wall im replacing...The braces look like Purlin Struts (but they just go to one of the common roof rafters)
I was trying to get an idea of loads but from what I can tell this is not much of a load bearing wall...
There in n snow load either
Initial plans ar to install a 14 ft LVL beam 13/4x10" above the joists and use Long joist hangers to tie to the beam
Your thoughts
Submitted: 1 year ago.
Category: Structural Engineering
Expert:  StructuralEng replied 1 year ago.

I can help. Can I get back to you in a couple hours?

Customer: replied 1 year ago.
i will await your answer
Expert:  StructuralEng replied 1 year ago.

Thank you. I'm back.

Expert:  StructuralEng replied 1 year ago.

If you have those struts, I would assume that wall supports the roof. I can size the beam for you if you can give me the following information.

The length of the joists on each side of the beam.

The city and state so I can look at snow loading.

I can size the beam, but you will need a detail to provide lateral stability to the beam since the top will not be braced by joists or sheathing.

Customer: replied 1 year ago.
ok i will have to look them up in the morning
Expert:  StructuralEng replied 1 year ago.

Thank you

Customer: replied 1 year ago.
there are only about 5 struts over the 12 feet of the beam and from what I can tell they are there to help prevent sagging of the roof rafters since there is no knee walls
The joists are 14 feet from one side of the beam to the outer wall and 12 feet from the other side of the beam to the back outer wall
The location in in Atlanta Ga.
you have an excellent point on lateral stability ...I will provide knee braces from the joists to the side of the beam probably 4 on each side of the beam.
Customer: replied 1 year ago.
the more I see time in the attic like this, I see why most beams are installed from below setting in pockets i.e. on top of 4x4s like I have done before, sure would elmiminat the problems you bring up
Expert:  StructuralEng replied 1 year ago.

If the struts are restraining movement then they are taking load. If they are not taking load then they wouldn't be helping with deflection.

Customer: replied 1 year ago.
still await your answer
Expert:  StructuralEng replied 1 year ago.

I apologize. I completely missed the dimensions you provided. I will size the beam and post the size in the next hour.

Customer: replied 1 year ago.
no problem
Expert:  StructuralEng replied 1 year ago.

You will need a 7" x 11.25" 2.0E LVL to work for strength and limit deflection to L/360.

Customer: replied 1 year ago.
thank you for the help but i have a question or two ...The beam you describe is bigger then the one in the crawl space below this wall. It is only 3-2x10 dimensional lumber (supporting the first floor and the roof)...Can you tell me the loading you used ---25lbs/square foot for the roof or what it was and the section modulus calculated...
Expert:  StructuralEng replied 1 year ago.

It's not just section modulus, that's for strength. LVL are almost always controlled by deflection.

I used 30 Psf live load (3/4 of the attic and roof combined) and 25 psf dead load (10 for attic and 15 for roof). The required moment f inertia for L/360 deflection is 813. The actual moment of inertia is 830, so it's pretty lean for that deflection ratio.

Expert:  StructuralEng replied 1 year ago.

Hello. Do you have any other questions for me on this topic? If you could rate my answer, I would appreciate it.

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