main beam

How can I tell if this beam is undersized? I mean everything about this looks wrong

Was it sagging or did it have another issue that makes you want to decide if it is the correct size?

No it wasn’t sagging. The only reason I even thought it honestly is just because it looked really thing compared to main beams in other homes that I’ve seen.

Site was down for a while…

Anyway, most all beams that I see are triple 2xs, depending on the span. If there is no defect, don’t invent one.

If you do not know or are unsure…

Newer metal post and additional reinforcement 2x6 posts are owner modified structural repairs, unable to determine if repair work is effective or safe. Recommend consulting with a structural engineer or other qualified person to determine if beam and supports are structurally safe and sound.

Or something like that.

Looks like it was built before the (inter) national building code.
The code tells you what the span (distance between columns or supports) should be depending on the dimensions of the beam and what it is made of. That it appears to be about 100 years old tells you it is probably fine.
If you want to be absolutely sure of it, refer to an engineer.

Span tables are available Aaron based on not just the spans but size of Beam, Live load, dead load, etc. You don’t give enough info here.

It is impossible to say without doing a complete structural analysis.

In short, one needs to calculate the tributary area supported by the beam and then figure out all dead loads.

Live Load would then be whatever the local building code specifies (40 psf most likely)

You then need to calculate 2 things.

  1. Bending moment in the beam and compare it to the moment of resistance of the beam.

  2. Unfactored Live Load Deflection.

In order for the beam to be OK, it needs to satisfy both of those.