Cast Iron sewer line replacement

[swp]

I am remodeling my bathroom and I plan to replace all of the pin holing cast iron I have. The bathroom is on the first floor and I plan to replace all of the cast iron from the roof down to just above the basement floor. currently its 3" cast iron pipe. I will be adding a basement bath a couple months from now and I also might add a master bath down the road a year or two from now.

Currently it is:
- kitchen sink
- bathroom
- sink
- toilet
- shower/tub

This is all on a 3" cast iron.

I plan to add in 3-6 months:
- basement bath
- shower
- toilet
- sink
- bar sink


Possibly adding 1-2 years from now:
- master bath
- shower
- tub
- toilet
- double vanity

Since I plan to add more I am pretty sure I should use 4" PVC for the main stack, when I go to do the basement bath I will crack the floor and replace the rest of the cast iron to the outside. The connection will be about 3-6 ft above the basement floor and vertical, and I can place a clean-out above. It will only be temporary till I crack the floor.

so my main questions are:

Is it going to be a problem going from 4" PVC to the 3" cast iron on the vertical run for a couple months?
Is a clean out above needed?
do I even need 4" PVC with the above future load?
Any recommendations for coupling the 4" PVC to 3" cast iron?

Final question is for the first floor bathroom. I want to hide the toilet sewer line in the floor joists till it gets to the basement wall about 3-4 ft at a 1/4" per foot that's about a 1" drop. When going to the wall it will be perpendicular to the wall, and when it gets to the wall I need it to run change direction 90 degrees and drop under the floor joist and run parallel with the wall.

Will I run into any flow problems with this drop and direction change, how far should or could it drop?
Or is this a no no, and I should just slope it to the main line and bulk head it?

(I really don't have much head room as it is in the basement about 7ft exact without drywall and flooring.)

Thanks ahead for the help!

 

[Jadnashua]

Find a fixture unit chart, then using what you think will be the maximum amount of things eventually hooked up, see what size drain the code requires.

 

[Sponsor]

 

[swp]

So looking at DFU:

master bath
shower 2
tub 2
sink 1
sink 1
toilet 3

total: 9

second floor total: 9

first floor bath
shower/tub 2
toilet 3
sink 1

total: 6


kitchen
dishwasher 2
sink 2

total: 4

first floor total: 19

basement
bar sink 1
laundry sink 2
washer 2

total: 5

basement above ground total: 24

basement bath
shower 2
toilet 3
sink 1

total: 6

under slab to sewer total: 30

So I have listed them by height.

Some key thins I see is that a stack less than 3 stories with 3" pipe can hold 48 DFU with max if two water closets. So that right there shows I can do 3" inches to the basement but then from the 3rd water closet under the slab I will have to go to 4". I stated before that I will be doing 1/4" slope with horizontal runs that means 3" can do 42 DFU horizontal with max 2 fixtures.

Looks like total I will have no more than 30 DFU so the only reason I have to go to 4" is going to be under the slabe becuase of the last bathroom.

thoughts? or agreements?

I added a rough sketch of the layout, vvery rough just to look at the load.

Thanks again !