If you’re installing a new bathroom, you’ll have to vent all of the appliances in the room. Fortunately, all three can be vented on a single branch vent, which you can then run to the vent stack or directly outside. That should be relatively easy, especially if you’ve not yet put the drywall in.
However, installing a branch vent for your toilet, shower, and sink does mean following and adhering to specific plumbing code. You’ll also very likely have to drill through your wall supports, which will mean reinforcing them. Therefore, venting your bathroom plumbing is likely to take some time.
How to Vent a Toilet, Sink and Shower
Installing a new bathroom always means installing plumbing and under international plumbing code, that means installing vents.
Here, it’s important to vent any fixture which drains to the public sewer. That’s because air bubbles and sewer gasses can become trapped in your line, causing backup and overflow, or even toxic gas buildup.
Fortunately, the same plumbing code mandates that you can install up to three fixtures on a single branch vent. This means you can install your toilet, sink, and shower on the same vent.
Of course, you can also choose to vent the toilet separately and put the washing machine on the bathroom branch vent. However, this guide assumes you want a traditional branch vent with a toilet, sink, and shower attached.
This article also makes the assumption that you’ve already taken the drywall off or haven’t yet put it on. In addition, it assumes the actual drains are roughed in and all you have to do is install the vents.
Things You’ll Need
- 2” PVC pipe. This has to go from the trap on each fixture to the branch and from there to the main vent or outside.
- Two 2” PVC elbows
- 2” Sanitary tee
- 3” toilet drain fitting with 2” sanitary tee angled at 45 degrees OR a 3” Wye fitting with 2” branch
- 1 ½” wye or angled sanitary tee with a 2” branch
- 2” or 1 ½” angled sanitary tee (check the size of your main vent)
- Any additional elbows, curves, or bends you need to get the vent where you need it
- PVC cement
- Small hand hacksaw
- Larger saw
- Power drill
- Forster bit at 2 ½ inches
- Measuring tape
- Leveling line (string and chalk will do)
- Safety glasses
- Wood screws
- 2” x 4” wood beams (enough to reinforce every wall stud you have to drill through)
1. Measure the pipe
It’s always a good idea to measure how much pipe you need before you go to the hardware store.
Here, the easiest way to do the measurements is to use string and some nails to tie your points. If you take the time to mark the beams and already have a level handy, you can use this step to measure where the pipes should be.
To do this, start from the fixture on one side of the room and tie a piece of string to the pipe where the vent should be. Use an angle finder or a level to plot the angle of the branch vent up, at no less than a 45-degree angle. It may also be horizontal.
Then, plot the height based on the highest fixture. Here, that’s normally the sink.
The vent must be a minimum of 6 inches above the overflow level of the highest fixture. So, you can choose to connect your vents 6” above the sink. You might also choose to go higher. Tap a small nail into the wall stud at that height and wrap the string around it.
From there, you can do the same calculation for the fixture on the other side of the room. Plot the angle at no less than a 45-degree angle and tap a nail at the same height as the other nail. From there, you can measure up from the center fixture and tap a nail where it will intersect.
Finally, measure from the center of that branch to the main vent or where you’ll be venting outside.
Adding up all of those distances will tell you how much pipe you need. You’ll also have a good visual of the corners the pipe has to make, which allows you to calculate the angles you require and the additional pieces you’ll need.
2. Connect the Vents to the Fixtures
Figure out where you want to connect your vents to the drains. Here, there are many requirements. For example:
- Shower and tub vents must be at least 4” from the weir on the trap and no more than 8 feet from the trap.
- Toilet vents must be at least 4” from the weir on the trap and no more than 6 feet from the trap.
- Sink wet vents must be at least 4” from the weir on the trap and no more than 3.5 feet from the trap with a 1 ½” wastepipe. If you have an older 1 ¼” wastepipe, it can be no more than 2 ½ feet from the trap.
You can simply mark the locations on the pipe, use a hacksaw to cut it, and insert the fittings you purchased for these vents. Make sure the angled adapters point upright. You should wait to glue anything until you have everything in place.
3. Drill out the vent pipe
Use the nails and string you put up earlier to mark the center of each board you have to drill through.
If you can’t take your vent pipe up in a straight line, you’ll also have to drill through the studs at an angle. You’ll want to avoid this if you can, so try to extend the branch at the top and have straight vents if you can. This will save you significant time drilling the wall studs.
Use a Forstner bit to drill out enough space to fit the pipe through. You’ll want to use wood screws to attach a second 2×4 to every section you drill out to reinforce the wood.
Then, drill through that as well, making sure the holes line up. Importantly, it’s mandatory to reinforce the wall studs if the hole is more than 25% of the studs’ width. Because you’re using at minimum, a 2” Forstner bit (which your pipe might not fit through), you’ll have to reinforce the studs.
4. Run the Pipe
Measure out and cut your lengths of pipe. Here, a marker is the easiest way to mark cut lines. You can use a hacksaw or a rotary saw to actually cut the pipe.
However, you will want to deburr the edges with rough sandpaper or something like steel wool. Then, clean out the inside of the pipe before putting it into the wall.
Because you’ll have to cut the horizontal branch vent anyway, you can cut it in two or even three sections, so the hole lines up with the center fixture and where you intend to connect to the main vent.
Then, add fittings. Loosely connect everything and make sure everything fits together, with no unnecessary stress or bends. If you have to, widen or re-drill a hole to ensure the pipe fits properly.
5. Connect to the Main Vent
From there, you’ll want to put a sanitary T in your branch vent and connect that to your main vent or directly outside.
If you’re connecting to the main vent stack, you’ll want to cut that and inert a Wye fitting facing downward to connect your new branch. If you’re venting directly outside, you’ll have to drill through the exterior of your home and install a vent cap.
The option that makes the most sense for your bathroom depends on your home, the layout, and the location of the main vent. E.g., it doesn’t make a lot of sense to have to drill through half of the walls in your home to get the vent to the main vent stack.
On the other hand, if you’re already relatively close, it does make sense. For example, if you’re venting from the basement, it likely makes more sense to vent directly outside.
You may directly vent your bathroom branch vent outside with 2-3 fixtures attached. If you have more fixtures, you should split them onto more vents.
6. Glue Everything Together
Once you’re satisfied that everything is where it should be, you can go ahead and use pipe cement to glue everything together.
Make sure you apply pipe cement in a ventilated space. Use a mask if you can’t. You’ll also want to wear disposable gloves to protect your hands.
While this is a wet vent, most of it should never see water. However, you should still give the glue plenty of time to dry before running water into the plumbing.
If you still have questions about venting your toilet, sink, and shower, these answers should help.
Can a toilet vent be upstream?
Yes, your toilet vent should be upstream. The only purpose of the vent is to allow air and sewer gasses to escape outside instead of into your home. In fact, your toilet vent should always be upstream.
How far can a toilet be from a vent stack?
The toilet vent should be a minimum of 4 inches away from the bottom of the trap and no more than 6 feet away from the bottom of the trap. Otherwise, it does not matter how far the toilet is from the main stack.
What are the different ways to vent a toilet?
You can normally use a traditional vent, a common vent, a stack vent, an auxiliary vent, or even an air admittance valve to vent a toilet, although the last is not usually recommended. Read more about different ways to vent a toilet here.
Can a sink drain into toilet vent?
Yes. If your toilet vent goes horizontal below the overflow line on the sink, the sink may drain into the vent. For this reason, you should ensure that all horizontal vents are at least 6” above any overflow lines on attached fixtures.
Venting your bathroom, including toilet, sink, and shower, is a crucial part of installing plumbing. Without venting, your plumbing is very likely to back up because of air bubbles, which could cause overflow and weird smells. While venting your toilet sink and shower will take time, you can relatively easily do a good job of it.