Thread: Questionable girder span

The house was built in 1977. The back of the garage was extended approx 15 feet. A girder was installed where the back exterior wall was. The girder is 1/2 inch OSB sandwiched beween two 2x12. I never measured the span but I would guess 16 to 20 feet. It looks like it's overspanned to me but I'm not sure. Does someone know the max span for this type of girder? Any help is appreciated.

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I don't know if it's an optical illusion in the pic or not but that beam appears bowed and sagging. Did it look that way at the inspection?

Considering that it looks like there will only be snow/rain load it will probably be ok. Don't know how much the OSB adds.
Two 2x12 used to be acceptable around here for 16'-18' garage door openings. It started changing a number of years ago. Now most suburbs around here require either triple 2x12 or double LVL for a 2 car opening.

Yes, there is a slight bow in the girder. I think the photo makes it look worse than it is. This is not a header like you would install at the vehicle door. This is a girder that extends from one side to the other. It is supported by 1 4x4 on both sides. It was once the back exterior wall but the addition puts the girder close to the middle. It is now supporting the roof structure of the original garage and the addition. Hopefully the picture from the roof will help. You can see the improper slope at the roof to wall junction. This house has several issues like this. Last year we seen up to 4 feet of snow on the roofs. It made it through that but they may have shoveled. Thanks for all the help

If the trusses are 2' oc, which they appear to be, the span is 18 to 20'. The 2x's have a lot of knots, so probably #2 lumber, the osb provides minimal structural support if any so I think the beam is under sized. Also looking at the second picture with the dead valley and beautiful flashing work, I'm guessing this was done without permits, plans or any professional knowledge from anyone involved.

Also the valley may be woven wrong but I can't tell for sure from the pic.

fwiw.... osb or plywood "sandwich" is a common practice so you can make 2 pieces of lumber line up with 3 1/2 inch framing.

As for the span/design question.... I'd be pretty quick to tell them to chase down the plans/permits or get and architect or SE to look it over. Whenever I research the specifics of things like this it's usually just for my own knowledge. I don't want to be accused of trying to be an engineer.