I think I know what you are talking about because I just built the same
thing. If you could post a picture somewhere, that would help. I don't
think buying longer lumber is going to help you much.

These are some of the things I did to get a straight soffit.
Did you snap a straight chalk line on the overhead rafters?
Did you overlap your 2x2 joints with the osb?
Can you move the bottom of the soffit in or out by adjusting the horizontal
pieces that are connecting to the wall on the other side of the sofffit?
When you built the soffit, did you hang a straight mason line at the bottom
of the soffit as a reference?
Since its .5" off, will anybody notice other than you?

wrote in message
...
Finishing my basement and done with the framing. I have one soffit
that spans a 6" duct as well as an I-beam over the course of 25'.
They're offset a little, but instead of making a turn in the soffit,
I'm just installing one long soffit to enclose both. This will
provide a little extra room to put recessed lighting in the soffit as
well, which is needed. Since I can't purchase 25' 2x2's to build the
soffit from, I used leftover 2x4's, ripped into 2x2's and OSB to add
ridgidity. Because some pieces are 4' and others are 8', the soffit
ended up not perfectly straight, although it's only about 0.5" off
over the course of the entire 25' run. Is this the nature of building
soffits, or if I buy 16' 2x2's and redo the entire thing, will it look
much better? Any chance adding the drywall will "hide" the underlying
issue, or is it likely to only make it worse or more obvious?

Thanks