I had a 10' addition added after a fire and the beam the (worthless) contractor installed is sagging. The city inspector said it needs to be replaced with something suitable.

From photos I have it looks like single 4x6 (not LVL) that angles with the roof.

I live in the midwest so it need to support snow load too.

The distance, inside the house, from peak to outside wall is 25' (7.6m) and the beam spans 19.5' (6m) wall-to-wall.

Thank you.

2 Answers 2


What Nate said in his answer is true, but need to go a bit further on this question. There are several charts available that specify beam sizes based on span, spacing and types of materials used. A beam 20 foot long would be difficult to create with dimensional lumber, but not impossible. You will be more likely to find that a LAM or steel beam will be required. Since you already have a negative input from the code enforcement folks, you may have to consult a reputable builder or structural engineer for guidance. I would not take any specific advice from a non professional in your case. Redoing this job will not be cheap, so do it right the second time. If the code officer will not tell you what they want to see, you will most likely be well served to have a spec certified by an engineer before proceeding.

  • If it is only replacing a single beam. I'd imagine that he could provide this information to the local building centre and they can plug the information in to give him what's required for the beam (they all have the software in my parts). I do however agree that an engineer stamped specification is the safest option.
    – Chris
    Aug 13, 2016 at 17:22
  • I know they will be able to spec a lam for your purpose and a good lumberyard. I wouldn't go to any box store for that stuff. Aug 13, 2016 at 18:06

You need to determine the spacing of the beams as well as the load or weight capacity. There is a formula but you need to consider those values to determine the size of beam. Also going to be pretty tough finding beams over 20 ft. Unless your using steel but expensive. Steel beams will be smaller than wood and are very handy for smaller spaces. I hope this will get you to the next point. Plugging all your numbers into the formula and there you have it

  • It's the only load bearing beam besides the peak. I found a load calculator but it wants wood species and spacing of the joists, which I don't have. I'll try a lumber yard and see if they'll give me an estimate. Contractors who've offered an opinion said 2 (1 said 3) 2x12 LVL but that'd double the height of the beam which I'm hoping to avoid. I'd probably spend a little more for a steel reinforced one or I-joist if it'd be the same size. Then we wouldn't need to cut the beams it sits on. The cost dif might be made up in labor cost.
    – DrTachyon
    Aug 14, 2016 at 5:46

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