Another Post About Soffits

Hurray!!! Soffits!!! or Bulkheads as I've learned they are called in some parts of the country.

Spent some time ripping down the old framing for the incorrectly done soffits.

This is the soffit for the exhaust pipe for the existing central heater.

Now you see it.

Now you don't

With the soffit gone you see the chase better.

This was where a chimney was and this chase goes alllllll the way up to the attic.

I'll spare everybody from all the before and after pics from the other soffits I removed, which look pretty much like whats above.

Fire Rated Chase Idea

I think that what I show above is the correct way to build a fire rated chase.
The drawing above is actually to scale.
Check out all those arrows!!! I luvs me some arrows.....

Additional Chase Questions

1. Whats a reasonable clearance between the HVAC trunk lines and the top/sides of the chase and to each other?
2. How much space should I leave below the trunk lines to run utilities?
3. What's the best way to run the utilities given the construction method of the soffit?
4. Does such a thing exist as a ceiling hung cable-piping tray? Is it code correct for me to run the utilities as shown?

Ducting Conundrum

Take a look at the diagram below.

The green boxes are the HVAC chases that I can make easily.
The problem is the right side of the plan.
That big red line represents where the old house ends and the addition begins.
I need to get two 7by8" HVAC trunk lines across that line.

Check out this pic of the area.

To the left I have a solid 4by12 under a 2by10 joist that I can not screw with.
Then, this entire wall will have to be sheared...
I'm stuck I can't see how to get the lines where they need to go.

Anybody got any ideas?