I have a 1924 house. The attic has 2x4 ceiling joists with 1x4 collar ties about 80" above the joists. The slope of the roof is 20/12. Below the collar ties there are two crossing 1x4 braces that are nailed, on each end, to the 2x4 rafters with 3 nails each. The braces seem to be resting on the top plate of the 2x4 walls (16 oc), but are not connected to the top plate. You can see a picture of the braces and collar ties here: https://drive.google.com/file/d/0B5hgKW1CXf-ZeThwQmZFSFQzems/view?usp=sharing
I'm wondering if there's a way to tell, based on the photo and info above, whether these braces and/or collar ties are structurally necessary (maybe this is a 1924-version of a truss?), or if they're potentially left over from the original construction before the roof was completed.
One final note... When I push on the braces they are pretty flexible. Not sure that means anything, but I guess my thought is that they'd be more rigid if they were under material tension.
Thanks for the opinions!