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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!

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2x4 rafters. I'm afraid those should be considered structural. Those rafters shouldn't really span that distance by themselves.

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    That's consensus. Definitely not removing those braces because both you and @Lee-Sam both pointed out those rafters are not big enough to support that roof on its own. – newbie Aug 17 '17 at 15:15
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Yes, they are braces for the 2x4 roof joists. They can be removed, but you'd need to "sister" a larger roof joist to the existing 2x4's.

Then, there are many additional questions: connections top and bottom, floor joists size, adding insulation in new roof joists, attic venting, electrical, heat, etc. AND if it's going to be a bedroom, you'll need a new egress window.

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    Got it. Sister those existing 2x4 rafters with something beefier and then you can potentially remove the braces and collar ties. And if you want to even expand up there, need to replace or sister the 2x4 ceiling joists as well, and make sure there's adequate room for insulation in the new, beefier rafters. You basically just read my mind because that's exactly where I want to go. Was thinking of the egress window being a giant dormer with french doors basically, but I know I'd need an engineer to suss out all the load here. – newbie Aug 17 '17 at 15:14

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