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walkereng, Consultant
Category: Structural Engineering
Satisfied Customers: 2546
Experience:  Over 30 years of Structural Engineering experience.
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I need to size a steel I beam for a 20 foot span in a house.

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I need to size a steel I beam for a 20 foot span in a house. It will carry a ceiling load and a partial roof load. The ceiling joist span is 12 feet each side of the beam of which they be hung off of. There is a strut every fourth ceiling joist that is connected to the rafters at a 45 degree angle on each side. The roof is a 5/12 pitch in central Minnesota snow load zone. Can you size the beam and corresponding posts and footings?


I can help


Let me read the question a bit closer


what city are you near, snow load can vary?

JACUSTOMER-led8l2zh- :



I seem to be having some trouble with the Chat feature, I am going to switch over to the Q&A format and we can continue with the e-mail process. Once I switch over, I will send you an e-mail, so check your e-mail. Thanks


I am here, are you able to see the e-mail?
Is the roof system resting on exterior walls that are 24' apart?
Customer: replied 4 years ago.
Ok, let me look up the exact snow load and then I will run some numbers and get back to you shortly. Are you set only on steel, or do you want to look at a Laminated Timber option also?
walkereng and other Structural Engineering Specialists are ready to help you
Customer: replied 4 years ago.
I am up for that as well, just thought that was getting a bit long on the span not to have a huge lvl or plam. Iwant to stay at 6 inch wide or skinnier for thickness so it will match point loads below. the timber would be easier for hanging the joists but I don't want to get to big. An I beam that is filled and bolted for joist hangers is what I figured, but am not opposed to skinny and tall in your option.
Customer: replied 4 years ago.

I hit accept answer by accident, sorry

You can use a W10x26 (50 ksi) steel beam. The beam is 5.75” wide, 10.375” deep, and it weighs 26 pounds per linear foot. You can use 3” diameter steel, schedule 40, standard pipes for supports.


You could also use a 3-1/2” x 18” Versa-Lam 2.0 3100 SP or DF. Your supports can be 4”x6” timber posts.

This is a Boise Cascade product and you can go to the following link to find distributors in your area.


Your concrete footings should be 30”x30”x12” deep. Use 4-#5 steel rebar in each direction and place them with a minimum of 3” of clearance from the bottom of the footing.

Customer: replied 4 years ago.
Can I get it shorter if I go with a 5.5 inch wide in that product
You could use a 5-1/2"x16" Boise Glulam 24F-V4/DF
Customer: replied 4 years ago.
I have a 30x30x10 deep footing with 2-#4x2'ea way on one end that has a 6x8 doug fir post that is taking a 17' foot span of floor load in the first floor. I am going to stack the post we are discussing on top of this. does this double load the footing or will I be ok
I sized the footing for the approximate 9,300 pound load at each end of the new 20' long beam. If you are trying to share a footing to support this new load and some existing load, the footing is not large enough.
Customer: replied 4 years ago.
the floor load matches the ceiling joist length and I have a w8x28holding up the floor at the 17'. If i can't swing this then I may have to go to figuring out how to truss my 24' span with using my existing framing in someway
You could increase your existing footing size by doweling rebar into the sides and pouring an extension.
Customer: replied 4 years ago.
sorry, already finished down there. Is trussing the existing roof span to eliminate the need for a beam a viable solution
You could, but it would have to be designed around your existing roof configuration. It would also be very labor intensive getting all of the materials into the attic, one by one, and then cutting them to size and mechanically connecting each one to make a truss.
Customer: replied 4 years ago.

No problem, I will open up the whole area by pulling all the rock in said area. I have 2x6 ceiling joists @ 16oc and 2x6 rafters @ 24oc . Its a hip so that may complicate it abit. lets just say that the entire room I am hoping to open up is 26' long with the 24' span. one end will have the tripod of commons and the other will be straight gable. 2x4 exterior walls @16oc. classic rambler

You should get a local engineer to take some measurements and give you a truss configuration and connection details.

Good Luck with your project!
Customer: replied 4 years ago.
i knew i would wear you out. thanks for the help, i appreciate it
Have a Good Weekend!

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