Advice on running waste pipe

[moa]

Hi there

I am planning for running a new waste line from the second story of my 1898 house to the crawlspace about 12 feet below. I will be running this through a stub wall which will give me a maximum diameter of about 3.5 inches. I have "as-built" architecture plans drawn up and will be applying for the requisite plumbing and building permits (I'm putting in a new bathroom).

So a few questions, the pipe will have to do something close to a 90 degree turn at the bottom of the 12 foot drop due to a major structual beam below the stub wall, and then extend about 20 feet to the soil stack. With a 1/4 over 4 inches drop, this works out to about 5 inches drop over the 20 feet span.

Q1. Is this angle too sharp? Would a long 90 degree span be sufficient?
Q2. Is the "new" cast iron pipe of an external diameter that can fit in this stubwall? Can I (should I) mix cast-iron for the drop pipe and then use ABS for the span (due to weight?)
Q3. Attached is a shot of my soil stack. Plan A is to cut the stack in the top span above the central Y, and put a new Y in in this place. Does this seem reasonable? Or due to the shortness of available pipe, should I chop the pipe lower and replace the whole shebang?

Q4. At the top of the pictured soil stack on the top floor is the Y tha went to the former toilet. I have since removed this but the Y and toilet mounting is still in place. How should I cap/dispose of this?

Thanks very much in advance
-Nick

 

[Sulconst2]

since im up ill give you my opinion. others will be able to give facts.
1/4 inch per foot is sufficient
to turn horizontal you need a long sweep y with a cleanout
should run pvc or abs the whole way from new bath to cast stack
if my house i would replace the "shebang" if you have a decent spot to snap above the floor. either way you have to support the cast above the cut. i could be wrong but I think im close.

 

[Sponsor]

 

[Casman]

I'd run the cast between the floors, it's quiet, I replaced with pvc and its very noisy, even with insulation and foam...

 

[Master Plumber Mark]

cast iron

the cast is quieter between the floors..

the 90 elbow will work just fine either on the
top or on the bottom

as far as fall 1/4 inch upstairs will work great

in the basement it wont really matter too much at all
because its going to be like niagra falls dropping
down from the second flooor..