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I have a single story ranch and am doing a reno by myself as a long-term project. Originally, the home was a small cabin and later it was expanded with addition.

The wall that I need to remove supports roof trusses which were originally part of the original cabin's roof. Left and right walls sit on the concrete perimeter foundation wall.

The span is 19ft and I am thinking about using 3x12" LVLs for this purpose (http://www.menards.com/main/storeitem.html?iid=1444438525506). I would love if someone could help me to determine if this is sufficient and I am interested in math, not in advice to hire an engineer.

LVL Size

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    What you are asking for is the engineering calculation. You need to supply many factors for this.. stud size / type of wood, square footage of roof, a layout of the existing supports
    – Eric F
    Apr 1, 2019 at 18:01
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    Doing the work yourself is quite admirable. Doing the engineering yourself - not so much. This would be a good place to spend some cash to have a qualified engineer spec the header for you. I guarantee it will be less expensive than rebuilding it should it fail, plus potential lawsuits if you renovate then sell.
    – FreeMan
    Apr 1, 2019 at 18:10
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    Seriously, get a structural engineer to do the calcs - so worth it - and you won't ever have to look at it and hope...
    – Solar Mike
    Apr 1, 2019 at 18:43
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    Is there an adequate footing under the posts?
    – Lee Sam
    Apr 2, 2019 at 17:02
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    This kind of structural change likely requires permitting. Getting that permit may require approval by an engineer. If you don't have any permits yet, or you permits don't include replacing that load bearing wall with a beam, then it's time to stop and fix your permits.
    – longneck
    Apr 2, 2019 at 17:13

5 Answers 5

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I see this question often in many forms so I will do my best to outline what is needed for a load calculation in general. Of course every house and roof is different so modify to get better results. Use a Factor of safety of 2.0 for structural loads. This means your resulting modulus should be 2 times what is required.:

  1. Determine the total weight of the roof. For a flat roof with snow loading 25 lbs / ft^2 is usually used and 50 lbs / ft^2 for rooms heavily walked on. Roof weight. Don't just use my estimates. Actually calculate it out as this is one of the major factors.

  2. Calculate maximum bending moment for each wood beam. This would be determined by how much load at a given distance a beam has to hold. For example if the span between two beams is 12 ft and 600 lbs is at this section then the maximum bending moment would be 12 x 600 / 8 = 900 ft-lbs. This should be determined per beam:

enter image description here

What a horizontal beam does is divide the load between the two beams that support it, so long as the horizontal beam itself can take the load. To determine if it can or can't, do a similar calculation, finding the section modulus it needs to support and what it can support. This means that for the beam to work it must meet two requirements: supporting itself and having the rest of the support beams not to fail.

Horizontal Beam

  1. Determine the beam's section modulus. Multiply the maximum bending moment found in step 2 by 12 to get inch-pounds and then divide that result by the allowable fiber stress in your wood beams to get the section modulus in inches cubed. This requires you to look it up depending on what type of wood you have. For example 1,150 lbs / in^2 is for pine 2 x 4's (Max fiber stress by wood types). Multiply the maximum bending moment of 900 ft lbs

Section Modulus Formula for Rectangle

enter image description here

  1. Calculate the section modulus for the different beams you could use.

Section modulus for a wooden beam = (beam width * (beam depth)^2) / 6

So for a 2 by 6 beam with actual dimensions of 1.5 x 5.5 inches this would be: 1.5 * (5.5)^2 / 6 = 7.6

  1. If the section modulus in step 4 is less than the required modulus times 2 (factor of safety) then the beam is not strong enough.

So for your question about determining if your LVL beam will be enough, plug in your beam's information to step 2, calculate out each stud to see if they are enough or not.

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  • For Step 1: 25*(20^2)=>10,000?
    – Andrew
    Apr 1, 2019 at 23:36
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    @Eric F This seems way to technical for the op to calculate. You give “extreme fiber strength” for pine in your answer, but lvl’s are considerably higher. Why not use a lvl chart? Each manufacturer knows what there product is capable of withstanding.
    – Lee Sam
    Apr 2, 2019 at 17:00
  • @LeeSam Many questions are asked on here that are more or less asking for an engineering structural analysis so I wanted to show what is involved in doing this. If the material is different then the max fiber stress number can be changed but either way the process is the same. I agree it may be too technical but it is still the process. I mostly wanted an answer I can reference when people ask what is involved. Do you think it is better if I ask the question and answer it myself separately?
    – Eric F
    Apr 3, 2019 at 12:35
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Nope, a 2 ply 1-3/4" x 11-7/8" LVL can't span that long with this much roof on it. With a 19' span (and completely guessing on the roof span and live loading for your area) you're looking at at least a 2 ply 24" LVL or a steel beam that would be impossible to install at this point.

The best solution to open this up is to run a 3 ply 11-7/8" LVL full length but with an intermediate support in the middle making two 9.5' spans with 1 beam. The intermediate bearing post will have 18,000+ pounds on it, so you'll need a PSL or steel column.

You'll also need a new column the same size directly below it in the basement. Your existing strip footing won't be able to handle a point load that large, so you'll probably need to pour a new pad with a bunch of rebar there, and that size changes based on your soil type and conditions.

So like the other answer said, get a contractor or an engineer to help you. I'm making educated guesses on everything based on one photo and knowing you want a 19' clear span, so take that for what it's worth.

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Proper approach - pay an engineer, that's their job. DIY guesswork engineering may cost you your house, with or without lives as well. Hardly worth the couple hundred bucks you might save.

Nearly as good in many cases - have your lumberyard make use of the canned engineering software that the LVL beam supplier may have provided them with to calculate the beam you need. If you provide valid inputs, it should spit out a safe answer, or tell you that it can't provide one.

You may need a truss, or a steel beam, or various other things depending on the precise situation and applicable loads. I won't speculate.

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I see what looks like an outside wall. 19' is going to be a huge beam that will impact the roof line unless you build a kick out wall from the outside wall. Going metal is the only way I see to ensure it to be small enough that it won't have a huge impact on the roof line. The last structural engineer recommended beam I put in was a glulam that stretched 14' and it was 17" high. Engineered was a bit smaller but not much.

The price I paid for the structural engineer calculations and recommendations on the correct beam was well spent money. No deflection of any kind, great peace of mind and it easily passed inspection.

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Here is what you do take 2_ 3 1/2 inch lvl beams and anchor them together and use 6x6 posts for a jack post and a king post and you'll be fine.

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  • Hello, and welcome to Home Improvement. There really isn't enough information here to answer the question. And, you should probably take our tour so you'll know how best to contribute here.
    – Daniel Griscom
    Nov 20, 2020 at 12:55
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    Voting to delete as this is extremely poor information at best.
    – FreeMan
    Feb 17, 2022 at 17:46
  • If the OP already cut the LVLs, then this isn't wrong. OP needs to go buy like two more LVLs though. And four or more 6x6s. And then not have a clear span anyway. If you cut something in half but then you quadruple its depth, but divide its span by four with posts, it's probably fine. - Is there a load bearing difference if they're a 3" instead of x2 laminated 1.5"?
    – Mazura
    3 hours ago

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