Water Closet DWV Design - Straight Vertical 4" Drain - Lifted Hous

[Csludtke]

Location - Florida

I am replumbing a home that was damaged by Hurricane Helene.
The repairs included "Lifting" a slab / block home and placing it on Columns.
During this process, all of the drain waste vent plumbing was removed

I need to replace the under-house DWV system. I am also replumbing the first floor DWV piping. I have a question

One of the Water Closets has a drain that is positioned in a manner that happens to very convenient to place a primary vertical 4" soil pipe without using any horizontal members until the Pipe is below the Ground.

I have attached a plumbing diagram for two bathroom groups. This is a very unusual setup. Looking venting specific code guidance.

 

[GReynolds929]

Whats the distance on the showers? Why use 4"? You only need 3". The aggregate vent area through the roof has to equal the size of the main building drain, if 4" you need 12.56 sq in of vent through the roof. If 3" you need 7.07 sq in.

 

[Sponsor]

 

[wwhitney]

The aggregate vent area through the roof has to equal the size of the main building drain, if 4" you need 12.56 sq in of vent through the roof. If 3" you need 7.07 sq in.

That's a UPC rule, Florida uses the IPC which does not have that rule. And even for the UPC, the required vent area through the roof is only required to equal the minimum allowable building drain size, not the actual building drain size installed.

Cheers, Wayne

 

[GReynolds929]

You are correct i am in a UPC state so thats what I'm familiar with.

 

[wwhitney]

I have attached a plumbing diagram for two bathroom groups. This is a very unusual setup. Looking venting specific code guidance.

The WC venting is fine, the vent through the roof dry vents WC-2, and that drain wet vents WC-1 (allowable under the IPC). On each shower, the total fall of the trap arm, from the trap outlet to the wye where the shower drain joins the lavs, is limited to one pipe diameter, or 2".

Cheers, Wayne

 

[Jeff H Young]

Location - Florida

I am replumbing a home that was damaged by Hurricane Helene.
The repairs included "Lifting" a slab / block home and placing it on Columns.
During this process, all of the drain waste vent plumbing was removed

I need to replace the under-house DWV system. I am also replumbing the first floor DWV piping. I have a question

One of the Water Closets has a drain that is positioned in a manner that happens to very convenient to place a primary vertical 4" soil pipe without using any horizontal members until the Pipe is below the Ground.

I have attached a plumbing diagram for two bathroom groups. This is a very unusual setup. Looking venting specific code guidance.

Dont see an issue venting ,As far as I know I never heard anything about a maximum length toilet waste can fall vertincal befor going horrizontal I guess thats what you are calling unusual or something about the vents ?

 

[Csludtke]

Whats the distance on the showers? Why use 4"? You only need 3". The aggregate vent area through the roof has to equal the size of the main building drain, if 4" you need 12.56 sq in of vent through the roof. If 3" you need 7.07 sq in.

4" Pipe was chosen for the Vertical Pipe due to align with the size of the Closet Flange (4"). I know that a 4" x 3" closet 90 deg is an acceptable way to reduce the size of the soil pipe. I am not sure that you can reduce the size of the soil pipe on a vertical drop. The 4" flange is embedded into the concrete.

 

[Csludtke]

Whats the distance on the showers? Why use 4"? You only need 3". The aggregate vent area through the roof has to equal the size of the main building drain, if 4" you need 12.56 sq in of vent through the roof. If 3" you need 7.07 sq in.

I will measure - it could exceed 12'
If it does, does the code allow you to transition to a larger pipe (3")? within a wet vent?

 

[Csludtke]

Thanks to all for you help

 

[wwhitney]

I will measure - it could exceed 12'

For wet venting, with a 2" shower trap (standard), you are limited to 8' maximum trap arm length. Because your fall is limited to 2", and your rate of fall must be at least 1/4" per foot. And to get to 8' trap arm length, you need to get your pitch perfect at exactly 1/4" per foot.

I guess you could use a 3" trap for a shower and bump that up to 12', but I've not heard of actually doing that. You could provide another venting method that connects to the shower fixture drain within 8' of the trap. And there might be some more exotic venting methods that could help.

But really the simplest thing is to redirect one or both double lav drains so that each shower fixture drain is hit by a vented lav drain within 8' of the trap.

Cheers, Wayne

 

[Jeff H Young]

An AAV might help on the showers and be easy access is required though

 

[Csludtke]

I will measure - it could exceed 12'
If it does, does the code allow you to transition to a larger pipe (3")? within a wet vent?

All wet vent lines will be less than 8’

 

[Jeff H Young]

problem solved