Duct Replacement

Hi,
I have a low pitched roof, and a 7" branch duct that crosses the main access route. The branch has gotten crushed on several occasions. The original duct was cardboard type material.
I built a little "shelf" to protect it, but it would be nice to have a little "play" in the duct.
It's about 7' from the trunk to the stackhead.
I've thought of a few options, but I'm not sure which would be best.
- Use insulated flex for the entire 7'.
- Use 3' to 4' of insulated flex right off the trunk, and use 3' to 4' of round metal pipe to the stackhead.
- Use 7' of round metal pipe, and hope it lasts longer than the old duct.
Any recommendations?
Thanks.
Eric
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Apologies for the spacing on the original post... You'd think that a cut and paste from Word to OE would work fine.
Eric
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Thanks for the suggestions.
I decided to replace the duct with rigid.
Took about 4 hours, start to finish. That included a trip to Lowes. It also included adjusting the height on the bridge to clear the new duct. Total cost was about $30, not including the tape, which I had.
Here are a couple of photos:
http://www.capitationservices.com/temp2.htm
Eric
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E. Hill wrote:

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lol. Nobody is doing any walking in our attic. Camera angles can be deceiving; those bridges are only 8" tall. If I remember correctly, there's only 28" of clearance at the ridge. Crawling is about all you do up there. Hence the crushing of the original duct.
I've been up in the attic more times than I care to count, and have never once came close to falling through. One of the first things I did was to lay planks in key areas so I could crawl around more easily.
Eric
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See my other post about adding supports to your bridge.
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