Shower venting

[Sawman]

I'm putting a small bathroom in an attic space above my garage. The walls of the room are placed directly between the attic truss such that I can't run a vent pipe in the wall for the shower. Cutting the attic truss seems like a bad idea so I need to vent from below.

If I run a 3" pipe within a foot of the 2" shower drain will it vent properly? Will the toilet suck the trap out without a vent between the the shower and the toilet? See the attached picture.

Thanks!

 

[Terry]

NOT Vented.
You need a vent before the shower enters the line with the toilet.
The toilet can't drop into a santee on it's back. Way better off dropping into a 90 then a wye fitting.
On a santee on it's back, the poop hits and spreads both ways. I've seen someone try your layout for a toilet and shower and it was filling the pipe with poop.
I would vent the shower using a wye or combo fitting, then bring it in the 3" line downstream of the closet flange and 90 bend. The shower then wet vents the toilet. The toilet can't wet vent the shower.

In this example, the lav wet vents the the tub and the toilet. Both the lav and the tub come in downstream of the toilet. The toilet is at the end of the line with a 90 bend.

 

[Sponsor]

 

[Sawman]

NOT Vented.
You need a vent before the shower enters the line with the toilet.
The toilet can't drop into a santee on it's back. Way better off dropping into a 90 then a wye fitting.
On a santee on it's back, the poop hits and spreads both ways. I've seen someone try your layout for a toilet and shower and it was filling the pipe with poop.
I would vent the shower using a wye or combo fitting, then bring it in the 3" line downstream of the closet flange and 90 bend. The shower then wet vents the toilet. The toilet can't wet vent the shower.

In this example, the lav wet vents the the tub and the toilet. Both the lav and the tub come in downstream of the toilet. The toilet is at the end of the line with a 90 bend.

Thanks for the quick reply! My drawing shows a santee under the toilet. It would have actually been a wye . . . I was thinking the large 3" pipe would help vent the shower. Looks like I was wrong about that!

My problem is that I can't find a good way to get a vent pipe to the shower side. I figured there is probably a slick way to get a vent pipe under the floor to the stack vent. Is it okay to run a wye from the shower drain and keep pipe under the floor, then wye into the vent stack? The vent would slope up to the stack. I have easy access to the vent stack but can't figure out how to run anything above the floor. My walls are dead nuts over and under the attic truss. The only way to get a pipe in the wall is to cut the truss. If there is a way to avoid cutting the truss I would rather do that. So far I have not seen a way to do what I'm asking. I suspect there's a reason for that . . .

 

[gking707]

Would the above image posted by terry be ok if there was no sink at all?

 

[Terry]

Would the above image posted by terry be ok if there was no sink at all?

The lav or sink allows you to snake the flat venting. The horizontal is 2" where the wet vent is which is needed rather than running that section in 1.5".
Without being able to clear the line there, it's better to keep the vent for the tub vertical.