If you’re installing a shower drain, international plumbing code mandates that you install a vent with it. Fortunately, installing a vent pipe is relatively easy, providing you know where the connection to the main vent pipe is.
Therefore, the process of venting a shower drain will vary slightly depending on if you have a new building or if you’re doing renovations on an existing home. However, it’s always a matter of running a diagonal pipe to the existing vent system.
Main Topics
How to Vent a Shower Drain
Shower vents allow gasses and air out of your sewage, effectively preventing buildup, bad smells, and air pockets which can cause backup and drainage problems. The following article covers how to vent a shower drain, providing you have a main vent stack in place. This article also assumes you’re connecting the shower vent to the toilet and the sink vents as well.
We’ve also made the assumption your wall is already open. Therefore, we haven’t included instructions on accessing your wall pipes. If you haven’t opened up your wall, you’ll want to take off the wall covering. You’ll also need access to the full space under the shower or the pipes in the back, so you can install the vent.
Additionally, you normally want to install a shower vent at the same time as when you plumb the shower drain. In that case, you can install both at the same time. In addition, you’ll want to install the drain vent before laying any concrete if you have a new floor.
Things you’ll need:
- 2” PVC pipe in a length suitable to go from the trap to the branch vent
- 2” PVC elbows and bends as necessary to reach the trap
- A 2” PVC T + a second T or corner depending on if you’re installing a new branch vent or cutting into an old one
- A power drill
- Forstner or spade bits
- A hacksaw (small and able to fit into tight spaces)
- Pipe cement
- Tape measure
- A leveling line or a string, nails, and chalk
- Safety glasses
- A level or angle finder
- If you’re installing a branch vent, you’ll want a 2” pipe in a length suitable to reach to the vent stack. You’ll also want a 2” to 1 ½” vent for the sink and a 2” T or corner for the toilet.
- Disposable gloves
- 2×4’s to reinforce the wall studs
- Wood screws
Measure your vent pipe
Figure out where you’re connecting the shower vent pipe. Legally, you can choose to vent directly outside, vent directly to the vent stack, or connect to a branch vent. Figure out where that connection should be. Then measure to see how much pipe you need to get there.
Your shower vent must be, at minimum, at a 45-degree angle. It may also be horizontal. This prevents water buildup and condensation.
In addition, if you’re creating a branch vent, the vent should lead up from the center of the branch. This means you want to connect your fixtures in a way that makes sense. Of course, if you have a nearby vent stack or if you already have a branch vent, you’ll just run the vent pipe to that.
Branching the vent from the drain
The first step to venting a shower drain is installing the vent on the drain. You can install the vent at any place in the drain, so long as it is a minimum of 4 inches from the weir on the trap and no more than 8 feet from the trap. Here, closer is usually better. The trap weir is the point at the bottom of the trap where it connects to the trap or U bend.
Here, you’ll want to align the T in a way that makes it easiest to get the pipe to the branch vent or vent stack. Then, glue it into place.
Drill out the vent pipe
Chances are, you’ll have to run your vent pipe through the studs. Here, you’ll want to trace the line you want to take using a leveling string or a string.
- Put nails in the studs where the vent pipe first enters the stud.
- Tie a string to the nail.
- Then, have someone else hold the string and pitch it to a 45-degree angle or steeper, so that it comes to the connection with the vent. If this isn’t possible, you can use a sharper angle, or you can go up at a 45-degree angle and then take a vertical turn.
- Use a level or angle finder to confirm the angle is correct.
- Place a nail in the stud and tie the string.
- Mark the angle of the string, so you can see the placement on each stud.
From there, you can take a drill with a power bit of Forstner bit. Drill holes in the center of each stud. If the hole is more than 25% of the stud’s width, you’ll have to double the studs with reinforcements. If you have 2×4 studs, you’ll want to double up the studs. To do so, simply cut a section that fits into the stud, use wood screws to attach it, and then drill through both.
Keep the holes drilled at the angle of the pipe going upwards. A right-angle bit is usually the best call.
If possible, it’s best to avoid drilling through the studs like this. This means that if you can get to the vent pipe by going straight up, that’s always the better call.
Run your vent pipe
Measure out your vent pipe sections and cut them. Lay them out with the necessary corners and connectors. Put everything in place and make sure it fits well. Then, use pipe glue to attach the pieces. It’s a good idea to use gloves when doing this work, as pipe cement can burn your hands.
Connect to the vent
If you’re connecting your shower vent to the end of a branch vent, use a corner to run the vent pipe into the branch. On the other hand, if you’re connecting to a vertical pipe, you’ll want to use an angled-T fitting to connect it. This will mean cutting the vent pipe, fitting the T, and then connecting all three together.
Do I Need a Shower Vent?
Every trapped rain is required to have a vent under international plumbing code. This means that your shower needs a vent to comply with building codes. In addition, your bathroom sink and your toilet also need a vent. For this reason, most bathrooms connect all three vents to a single, dry vent that runs up to the main vent stack or roof vent. This is known as the branch vent.
Shower Drain Vent Requirements
Shower vents are regulated under international building law. This is important because mistakes can result in a buildup of toxic gasses, flooding, and in sewage for the block not working. If you’re installing a shower vent yourself, it’s important that you follow building code regulations. In addition, not all city codes allow you to do the work yourself. You might want to check your local building code to see if it’s allowed before proceeding.
- Vents and branch vents must be connected above the centerline of the horizontal drainpipe.
- Dry vents should rise vertically to a minimum of 5 inches above the floor level rim of the highest trap being vented.
- Horizontal branch vents should be a minimum of 5 inches above the flood level rim of the highest fixture attached to the branch.
- A connection between the vent and the stack vent must be a minimum of 6 inches above the flood level rim of the highest fixture attached to the pipe.
- You may directly vent a shower or the bathroom (2-3 vents) through a common vent directly to the outdoors.
- A shower vent (2-inch drain) should be a minimum of 4 inches from the trap weir and a maximum of 8 feet from the trap.
- Vent pipes must be a minimum of a 45-degree angle from horizontal.
These requirements remain true whether you’re venting a shower in the attic, the basement, or anywhere in between.
FAQ
Installing a shower vent is relatively simple, but there are a lot of specifications. This FAQ should help.
How far should a vent be from the shower drain?
The vent should be a minimum of 4 inches from the trap weir and a maximum of 8 feet. Of course, that’s for a 2” shower drain vent. If you’re venting a tub or a sink, the distance changes. E.g., a 1 ½ inch sink vent should be 3 inches to 5 feet from the trap weir.
Can I put the shower and the toilet on the same vent?
Yes. You can run up to three fixtures to the same branch vent and then run that outdoors or to the vent stack. Some local building codes may vary. However, shared venting is very common for bathrooms. It’s important that your horizontal branch vent has a central upward vent duct to the outside or to the trap. This should be located in the center of the pipe and directly above the center fixture.
Does a shower drain need a vent?
Your shower may not drain. Your shower may also smell. In addition, you could experience a buildup of sewer gasses. In most cases, it means you’ll eventually have overflowing drains and toilets that won’t flush. Normally, that happens because air pockets and bubbles trap water and prevent it from flowing down the sewer.
Conclusion
Installing a shower vent can be a significant amount of work if you have to take off the tiling and the drywall. However, if you already have everything out or are putting in a new build, the concept is relatively simple. Providing you have a good angle finder; it should be relatively easy to put your vent in.
Hopefully, this article has taught you how to vent a shower drain and you now have a good idea of how to do the work.
