Plumb a Bathroom

Welcome to our comprehensive guide on how to plumb a bathroom! Whether you’re a seasoned DIY enthusiast or a novice looking to embark on your first plumbing project, understanding the intricacies of bathroom plumbing is crucial for a successful and hassle-free installation. From tackling the basics of pipe connections to mastering the art of fixture installations, we’ll take you step-by-step through the entire process. So, roll up your sleeves and get ready to transform your bathroom into a functional and efficient oasis with our expert tips and tricks. Let’s dive in and make your plumbing journey a rewarding one!

Note: If you don’t want to plumb your bathroom yourself and just want to get an idea of how it is done, it would be best to let the professional residential plumbers do it for you.

A Comprehensive List of DWV Fittings for Bathroom Plumbing

DWV Fittings for Bathroom Plumbing

Before diving into the plumbing process, it’s essential to have a clear understanding of the DWV (Drain-Waste-Vent) fittings required for your bathroom project. Remember that the specific fittings needed may vary depending on your local plumbing code, with the two significant regulations in the United States being the IPC (International Plumbing Code) and the UPC (Uniform Plumbing Code).

Below is a carefully compiled list of DWV fittings used to plumb a simple bathroom. Each plumbing code has its column indicating the number of fittings required.

DWV Fitting Qty in IPC Qty in UPC
1.5″ Sanitary Tee 2 1
2″x2″x1.5″ Sanitary Tee 0 1
3″ Sanitary Tee 1 1
1.5″ 90 1 1
4″x3″ Closet Bend 1 1
4″ Closet Flange 1 1
3″x3″x1.5″ Wye (w/ 45) 1 1
3″ Combo 1 1
1.5″ P-Trap 1 1
1.5″ Trap Adapter 1 1
3″ Cleanout Adapter 1 1
3″ Cleanout Plug 1 1
3″x1.5″ Flush Bushing 1 0
3″x2″ Flush Bushing 0 1


This comprehensive list will prepare you to tackle the bathroom plumbing project. However, before we proceed with the installation, there are essential aspects to consider, which will be discussed further. So, let’s get ready to transform your bathroom into a space that marries functionality with elegance and style.

Guide to Bathroom Plumbing Rough-In Dimensions

Bathroom Plumbing Rough-In Dimensions

Before you embark on your bathroom plumbing project, you must be well-acquainted with the rough-in dimensions required for various fixtures.

These measurements will lay the groundwork for a successful and installation that adheres to plumbing codes. Now, let’s delve into the essential rough-in dimensions for both the bathroom sink and toilet:

Bathroom Sink Rough-In Dimensions:

  • The lavatory’s drain’s center should be approximately 18 inches above the finished floor.
  • The drain should be centred right in the middle of a 30-inch vanity.
  • The bathroom sink’s water lines are roughed about 3 inches above the drain. Measure approximately 21 inches above the finished floor.
  • The hot and cold water lines should be spaced 8 inches apart from left to right. Measure 4 inches to the left and 4 inches to the right from the center of the drain.

Toilet Rough-In Dimensions:

  • The center of the closet flange should be positioned 12 inches from the finished rear wall.
  • If you’re measuring from an unfinished wall, remember to add the thickness to the 12 inches.
  • There should be 32 inches of total clearance between the finished side wall and the bathroom vanity, centring the toilet flange in the middle.

It’s essential to note that while 30 inches is the minimum distance allowed by the plumbing code, you can provide more clearance if desired.

As you delve into DWV fittings and bathroom plumbing, we understand that all these dimensions and fittings may initially feel overwhelming. However, fear not; the real excitement begins when you learn how to transform these components into a fully functional and code-approved bathroom.

Soon, you’ll be on your way to creating a stylish and efficient space that meets all your needs and adheres to the highest plumbing standards. To further understand the process of roughing in a closet flange, we recommend checking out our accompanying article or downloading our “Plumbing Diagram” for an easy-to-understand visual aid.

Get ready to embark on this rewarding journey of bathroom plumbing mastery!

How to Plumb a Bathroom Sink?

How to Plumb a Bathroom Sink

Attention to these crucial dimensions and fittings will ensure a smooth and code-compliant plumbing installation.

Bathroom Lavatory Rough-In: The bathroom lavatory is roughed-in with a 1.5″ sanitary fitting in the vertical position. This results in the following dimensions:

  • Bathroom sink drain: 1.5″
  • Vent: 1.5″
  • Trap arm: 1.5″
  • P-trap: 1.5″

Connecting the Plumbing Under the Bathroom Sink: To connect the Plumbing under the bathroom sink, you’ll need a 1.5″ trap adapter and a 1.5″ plastic tubing P-trap, sometimes called a trim trap. The Trim Trap kit includes two different sizes of washers. Use the 1.5″ x 1.25″ slip joint washer to connect the P-Trap to the lavatory’s 1.25″ waste outlet.

Bathroom Sink Plumbing Diagram: Refer to the bathroom sink plumbing diagram below to visually represent the connections.

P-Trap vs. S-Trap: Important to note the Plumbing used here is a P-Trap, not an S-Trap. If you encounter an S-Trap, refer to the appropriate article for guidance.

Vent and Trap Sizes: Both principal plumbing codes in the U.S. allow a single basin lavatory to be roughed in with a 1.25″ vent and a 1.25″ trap (IPC Table 709.1 or UPC Table 702.1). However, in this example, we use all 1.5 inches for consistency.

Vertical to Horizontal Transition: When waste transitions from a vertical pipe to a horizontal line, always use long pattern DWV fittings. In this case, you have two acceptable options:

  1. Wye with 45.
  2. Combination Wye and 1/8 Bend (Combo Fitting).

The choice here is a 3″ x3″ x1.5″ wye with a 1.5″ street 45.

Toilet Drainage: For the toilet drainage, use a 4-inch closet flange connected to a 4″ x3″ closet bend (4 inches on the inlet and 3 inches on the outlet). The outlet of the closet bend connects to a 3-inch sanitary tee using a short piece of 3-inch PVC. Observe another vertical-to-horizontal transition in this section.

Vertical to Horizontal Transition Fittings in Bathroom Plumbing

Vertical to Horizontal Transition Fittings: For vertical to horizontal transitions, the plumbing code permits using Long Sweep Fittings (A) but not Short Sweep Fittings (B). Therefore, the chosen fitting is a 3″ combo (combination of Wye and ⅛ bend).

clean out plug in bathroom plumbing

Cleanout Plug: Finally, in the plumbing diagram above, you’ll notice the cleanout plug, an essential component for easy access and maintenance of the drainage system.

Enhancing Bathroom Plumbing: Adding Cleanout and Alternative DWV Fittings

Adding Cleanout and Alternative DWV Fittings

To ensure a comprehensive bathroom plumbing setup, it’s essential to incorporate a cleanout for easy access and maintenance in case of blockages. Adding a cleanout requires two additional fittings: a 3″ cleanout adapter and a 3″ cleanout plug. The cleanout adapter seamlessly attaches to the inlet of the combo fitting, providing a convenient access point to rod the drain if needed.

By the way, other DWV fittings can be utilized for vertical-to-horizontal transitions. These alternatives include:

  1. Wye with 45
  2. Long Turn 90
  3. Two 45’s

Moving downstream in the drainage system, you’ll observe how the bathroom’s 3-inch drain wyes into the building drain. A 3-inch wye (with 45) is utilized in this case, although a 3-inch combo fitting could also be employed for this connection.

Now that you understand this bathroom’s drainage system and the necessary fittings let’s shift gears and discuss other vital aspects of bathroom plumbing to create a fully functional and efficient setup.

Importance of Bathroom Plumbing Vents

Bathroom Plumbing Vents - O Plus Plumbing Inc. | Leading Plumbing, Plumber & Drain Company in The Greater Toronto Area - Professional Plumbing & Drain In Toronto and GTA

In any plumbing system, it is crucial to ensure proper venting for each fixture to maintain a functioning and safe environment within your home. The primary purpose of plumbing venting is to protect trap seals, which are essential for preventing sewer gas from escaping into your living spaces.

Trap Seal Protection: The trap seal, located inside the P-Trap of each fixture, acts as a barrier against sewer gas. When wastewater flows through the drainage system, it creates air pressure fluctuations that can disturb and remove the trap seal. Once the seal is lost, unpleasant and harmful sewer gas can enter your home.

Conventional Venting Method: One of the most widely used venting methods is called “conventional venting,” where each plumbing fixture has its vent, known as an individual vent. In this method, the vents control pressure fluctuations, ensuring the trap seal remains intact inside the P-Trap.

Sizing Individual Plumbing Vents: The size of individual plumbing vents varies depending on your plumbing code. In the IPC (International Plumbing Code), toilet vents are typically 1.5 inches, while in the UPC (Uniform Plumbing Code), they are 2 inches. To connect the appropriate-sized vent into the hub of the 3″ sanitary tee, you’ll need a flush bushing, which looks similar to hockey pucks. In the IPC, use a 3″ x1.5″ flush bushing, while in the UPC, a 3″ x2″ flush bushing is utilized.

Bathroom Plumbing Diagram: For a comprehensive overview of the bathroom plumbing, you can refer to a detailed 3D CAD drawing, clearly labelling each DWV fitting for both IPC and UPCs. This diagram will guide you throughout the plumbing process.

Bath Lav’s Individual Plumbing Vent: The bathroom sink (lav) has its vent, sized at 1.5 inches (1.25″ as per code minimum). It’s important to note that the vent offsets horizontally well above the lav’s flood level rim (FLR), ensuring proper ventilation and adequate trap seal protection.

Plumbing venting is an essential aspect of any plumbing system, ensuring that the trap seals remain intact and preventing the intrusion of sewer gas into your home. Following proper venting techniques and adhering to plumbing codes, you can maintain a safe and odour-free environment in your bathroom and throughout your house.

Horizontal Plumbing Vents in Your Bathroom Need To Be Sloped

Importance of Sloped Vent Pipes and Proper Venting in Bathroom Plumbing

In bathroom plumbing systems, vent pipes are crucial in maintaining proper drainage and preventing potential issues caused by water vapour condensation and rainwater intrusion. Ensuring the correct slope on horizontal vent pipes is essential to address these concerns effectively.

Condensation and Rainwater Concerns: Water vapour has the potential to condense inside vent pipes, while rainwater can also find its way into certain parts of the venting system. To counteract these issues, it’s essential to incorporate a slight slope on horizontal vents. This slope allows any water vapour to drain back into the drainage system, aided by gravity.

Sloped Venting in IPC and UPC: In the IPC (International Plumbing Code), horizontal plumbing vents must be sloped to effectively address water vapour and rainwater concerns. However, in the UPC (Uniform Plumbing Code), a provision allows for a horizontal level vent without any grade as long as it is positioned above the flood level rim (FLR). It’s important to note that horizontal vents in the UPC cannot have sags or drops.

Connecting Bathroom Sink and Toilet Vents: An essential connection in bathroom plumbing is between the bathroom sink’s vent and the toilet’s vent. To achieve this, an appropriate-sized sanitary tee is placed upside down.

  • A 1.5″ sanitary tee (upside down) is used in the IPC.
  • A 2″ x2″ x1.5 San tee (upside down) is utilized in the UPC.

This vent can terminate through the roof independently or be tied into the home’s existing venting system.

Increased Vent Size in Cold Weather Climates: In regions with cold weather climates, it’s crucial to increase the size of plumbing vents before extending them through the roof. This increase prevents the vent from closing due to frost, ensuring proper venting during cold temperatures. Local codes typically specify the appropriate vent size increase, usually around 3 inches. Additionally, this increase should be made within the building’s thermal envelope or the heated portion of the home.

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