Flex duct support graphic.

Must admit {D} gave me a laugh.

Can be supported by ceiling joists if the support is at least every 4 feet.

I get it though as you are thinking parallel and in them between no doubt.

Maybe timber framing could have joists 4’ apart. I can’t think of any other scenario offhand.

You left out the most important item of all (how to properly attache a flex duct to a ridge connector or sleeve):wink: