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?

How Best To Build A 1hr Fire Rated Soffit?

I need a good method to build 1hr fire rated soffits. Anybody got any good ideas?

Currently the soffits look like this.

These are wrong because the wall behind and the joist bay above is not fire stopped.
I've talked to my BI and he says to use 5/8" firecode drywall on the underside of the joist bay and on the wall.

Okay, that seems easy enough, but in practice how are things like this done? I've never built one before.

I will have to build at least two soffits, probably on either side of the center load bearing wall to conceal the HVAC trunk lines. Actually, I haven't been able to decide on the best way to run the soffits...got any ideas?

HVAC Duct Diagram

Was that easy to understand? It wasn't for me first couple of times I looked at it.
This is two separate systems. One for the basement apartment and one for the main floor of the house.
How best to proceed?
It seems like I have to remove the existing soffit framing.
Then install the Sheetrock on the underside of the joists and the wall studs, but only the part where the soffit will be.
Then run my HVAC trunk line with top take-offs that penetrate the fire-stopping.
Then run what ever else I need to in the same area.
I would like to use this soffit as a chase for everything I can (no drilling through joists if I can help it). I can envision running water, gas, low-voltage lines (cable, Ethernet, phone) and romex.
As long as I correctly firestop the penetrations of the soffit is there a reason not to do this?

Simple Soffit Construction?
Then after everything is run in the soffit area I would build and attach the bottom and the one side.
I think I remember reading somewhere about a simple method to do this.
No elaborate 2by4 framing but I can't remember where I read about it.
I mean, the 'framing' of the soffit only needs to be strong enough to support the 5/8" drywall right?

Anybody got any helpful ideas?