Can The Plumbing Vent Run Horizontally? (Explained)

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Plumbing vents are often installed on the roof of a house. It is not uncommon for people to wonder if they can install their plumbing vent horizontally, rather than vertically. So is this possible?

Vent pipes can have horizontal lines, provided you take caution to ensure they can’t be plugged with water. Ensure that any water that gets through the vent opening can run out to the sewer without blocking the flow. Moreover, the horizontal vent should not run more than 20-25ft across the attic.

Can A Plumbing Vent Go Out A Wall?

While a plumbing vent can go out a wall, it shouldn’t extend for more than twelve inches above the roofline since it may result in freezing of the condensation.

When the condensation inside the sedition above the roof freezes, it results in blocking of the pipes. Remember to install proper flashing around the pipe if you have to cut through the soffit. This is in a bid to prevent water from seeping beneath the roof covering.

Fortunately, since the plastic pipe is paintable, you can camouflage a vent that goes out a wall by painting it the same color as your house. According to Brady Home Inspection, the vent is an important part of your drainage system and is responsible for performing two main functions.

Firstly, it allows air into the drain, thus replacing created by previously flowing water. Its second functions include facilitating the escape of sewer gases from the pipes, which diffuses in the outside air.

Research by Fantastic Viewpoint suggests that in order to achieve the second function, the top of the vent must be at least one foot above the roof and at least ten feet from windows or doors.

Moreover, the research advises that while the vent can pass through the roof; it can also pass through the wall, rising above the roof. Here are some important instructions to follow if you want to route the vent out of a wall.

Here are some of the tools you’ll need for the project:

  1. 120-grit sandpaper
  2. Hacksaw
  3. Reciprocating saw
  4. Hammer
  5. Cold chisel
  6. 2 long-sweep elbows
  7. Caulk
  8. Pipe strapping
  9. 1 1/2- or 2-inch plastic pipe
  10. Sanitary tee


Use a hacksaw to cut into the drainpipe you wish to vent. However, to guarantee the vent’s effectiveness, ensure that you cut within five feet of the drain P-trap.

With 120-grit sandpaper, deburr both the cut ends of the pipe and use plastic pipe cement to stick a sanitary tee between them. Ensure that the outward of the tee faces upwards and has a diameter of 1.5-2 inches. Lastly, check to ascertain that the sweep angles toward the sewer.

Extend about two inches of the plastic pipe upward up to where the pipe will exit the wall. Although the pipe will extend horizontally in some sections, ensure that it maintains a ¼-inch slant per foot at all places when it approaches the drain.

Using a pencil, trace the outline of the pipe’s cross-section on the wall and use a reciprocating saw to cut the design. The hole’s diameter should measure about ¾ inches, which is larger than the pipe.

This is to ensure that there is enough room to attain the ¼ inch slope per foot. If the wall siding is brick or stucco, you may be required to chip some of it out to get enough room. Use a hammer and cold chisel to chip the hole out.

Extend a pipe through the hole, which extends a minimum of twelve inches from the exterior wall. Connect it to the vent line using a long-sweep elbow while taking caution to maintain the required slant towards the sewer. Glue another long-sweep elbow onto the other end while ensuring that the elbow’s outlet faces upward.

Glue a length of pipe extending twelve inches over the roofline to the elbow. You can create a hole in the soffit and pass the pipe or use pipe strapping to clamp the pipe to the roof fascia.

Clamp the vertical pipe to the house on the side having pipe strapping. Next, spray expanding foam insulation through the hole to which the pipe extends to ensure that it remains waterproof.

Give some time for the foam to expand and set before using a utility knife to cut it flush to the wall. Finally, paint the pipe to match the wall.

Does A Plumbing Vent Pipe Have To Be Straight?

Plumbing vent pipes have to be straight, especially on the vertical, to facilitate for proper flow of air into the system.

Otherwise, if a plumbing vent isn’t straight, chances are high for vapor locks to occur.

Bends in a vent pipe result in the accumulation of moisture which gets trapped. Moreover, since the vent pipe is usually warm throughout the year, water trapped in a bend may turn into vapor, thus resulting in a vapor lock.

With a vapor lock present in the pipe, the vent won’t work as it is intended.

Plumbers install plumbing vent pipes to allow airflow into the plumbing system, thus enhancing the performance of other drains in the house.

This is because all other piping using the house feature bends. Hence, they have to be attached to the venting system for optimal performance.

Ensure that the plumbing vent is at the recommended 90-degree angle when using 45’s and 90’s to connect to the plumbing vent.

Otherwise, if you don’t adhere to this rule, you risk having vapor locks in the plumbing vent, thus preventing proper venting.

Since the vent ought to run horizontally for twenty to twenty-five feet across the attic to the vertical pipe passing through the roof, you can use a sanitary tee when connecting a horizontal run. This includes a waste arm to a vertical riser or vent stack.

Can Vent Pipes Have Bends?

There is no considerable harm in having ¼ bend in your vent pipe. Although vent pipes normally run plumb or level, you may need to include a bend, especially if you are working your way around an obstacle.

However, whichever way you install your vent pipes, ensure that they remain dry. Also, you can install 90-degree bends in vent pipes.

As per the 2006 International Plumbing Code, all branch vent pipes and the main vent pipe should also be connected and graded in such a way that allows them to drain to the drainage pipe via gravity.

This may prevent you from having bends in your plumbing vent since the lower horizontal connection will slope toward the stack.

As expected, call out the 90-degree fitting since it is impossible to lay a typical 90 on a waste line horizontally. Instead, you can use a long sweep of 90 or two 45’s at minimum. However, since you need to repair it anyway, use the single 45 as I mentioned above.

How Many Elbows Can A Plumbing Vent Have?

Plumbing vents in the past used to be mostly straight, with a single 45-degree elbow. However, things have changed, and most local plumbing codes allow up to two 90-degree bends.

This means that you can use two elbows in your plumbing vent. However, ensure to use elbows that feature a wider radius. While you may use vent piping, you can’t have the tight 90-degree elbow- which is also known as a vent elbow, especially if the joint is below water level (the level of your sink.)


Since vent pipes supply fresh air to every plumbing fixture in a house, it enables the system to move water through drainage pipes every time you drain your sink or flush the toilet.

In addition, including plumbing vents in your system allows wastewater odor and gas to escape while at the same time preventing sewer gases from entering the house.

You can install vent pipes to exit the roof in locations where you find the least objectionable from what I’ve witnessed. Depending on your preference, you can easily relocate your vent pipes. However, take caution to ensure that you avoid as many sharp bends as you can.

Meet Marco, a lifelong tinkerer and DIY enthusiast, developed a passion for plumbing after fixing a leaky faucet in his own home. Years later, he turned that passion into a thriving business, Amarco Plumbing, where he shares his knowledge and expertise with the community.