What are the Rough In Dimensions for a Tub Drain? The Ultimate Guide for Homeowners

Hey there! If you‘re taking on the project of installing a new bathtub, getting the rough in plumbing right is crucial before you close up those walls. Improper drainage from an incorrectly sized or placed tub drain can cause major headaches down the road.

As a home improvement pro who has tackled my fair share of bath remodels, I‘ve put together this comprehensive guide on tub drain rough in dimensions to help homeowners like yourself get it right the first time. We‘ll dig into all the nitty gritty details, from properly measuring for the drain opening to ensuring adequate ventilation.

Let‘s Start With the Basics: What is a Rough In?

The "rough in" stage happens early on in the tub installation process, before the finish materials like tile and drywall are installed. This involves getting the main drain line installed below the floor, along with hot and cold water supply lines and cutouts for faucets and shower heads.

The most important part of the rough in is installing the bathtub drain assembly into the subfloor. This includes cutting an opening for the drain, positioning the drain outlet correctly, and tying the drain into the home‘s waste ventilation system.

Getting these drain dimensions right during the rough in stage ensures proper drainage and leak-free operation for the life of the tub. It also avoids having to break open finished walls later on for drain repairs or replacement.

Why Proper Tub Drain Dimensions Are Essential

You might be wondering why it‘s worth sweating the small details on properly sizing and placing the tub drain rough in. Here‘s why getting it right matters:

• Prevents Water Damage: An incorrectly cut drain hole or improperly sloped pipe can allow water to pool under the tub and leak into subfloor or walls.

• Avoids Clogs: If the drain hole is too small or the pipe too narrow, it can easily get clogged with hair and debris.

• Reduces Leaks: A drain pipe that‘s too small or fitted together improperly can leak over time.

• Allows Proper Drainage: Correct height and position allow the tub to drain fully without leaving standing water.

• Limits Sewer Gas: A well-vented drain prevents sewer gases from backing up into the home.

Following manufacturer specifications for drain hole size, height, position, pipe diameter, and venting is the best way to avoid these types of problems.

Key Measurements for Tub Drain Rough Ins

When installing the tub drain rough in, there are some key measurements that are important to get right:

Size of the Drain Hole

• The hole cut into the subfloor should be 5 1⁄2 to 6 inches in diameter.
• Leave a 1/8 to 1⁄4 inch gap between the drain pipe collar and the hole.
• Adapt hole size if needed to fit drain assembly.

Height of the Drain

• Top of the drain outlet should be 6 1⁄2 to 8 inches above finished floor.
• Bottom of drain must be 1 1⁄2 to 2 1⁄2 inches above subfloor.

Position of the Drain

• Center of drain hole should be 12-16 inches from wall studs.
• Minimum 1 1⁄4 inch space between drain outlet and waste pipe.

Vent Connection

• Tie vent in 4 to 6 inches above bottom of drain pipe.

Getting the drain height and position right ensures proper drainage slope. Follow your tub‘s specifications!

Selecting the Correct Pipe Diameters

Choosing the right sized pipes is also key for keeping things flowing freely.

Bathtub Drain Outlet Pipe

• Use a 1 1⁄2 or 2 inch pipe for the drain outlet.
• Match the diameter to the drain flange size.

Vent Piping

• Should be 1 1⁄2 to 2 inches in diameter.
• Match the size of the drain outlet pipe.

Main Drain Line

• Use a 2 inch diameter pipe for most tubs.
• Larger 3 inch drains are needed for over 60" tubs.

Matching pipe sizes correctly optimizes drainage and decreases clogging risk.

Digging Into the Details on Drain Traps

You‘ve likely heard about the importance of drain traps. Let‘s look at what types are used for tubs and why they matter:

What Does a Trap Do?

A drain trap holds water in the drain pipe to block sewer gases from entering the home. The water seals the pipe while still allowing drainage.

Types of Bathtub Drain Traps

There are two main varieties used for tub drains:

• P-Trap: The most common. Shaped like a "P" with vertical and horizontal sections. Easy to install and clean.

• S-Trap: Also called an S-bend. Has horizontal slip joints shaped like an "S".

Advantages of a P-Trap

P-traps are recommended for bathtub drains for several reasons:

• Drain water efficiently due to less horizontal run.
• Easy to inspect, clean, and remove clogs.
• Can handle greater flow rates than S-traps.
• Require only a minor curve to tie into the drain line.

Make sure any tub drain trap you use meets the required local plumbing codes.

Achieving a Watertight Seal

To prevent leaks, it‘s crucial to seal all connections properly:

• Pipe Dope/Tape: Use on threaded pipe connections.

• Overlap: Slide slip joints together fully to meet code.

• Silicone/Putty: Seal drain flange fully.

• Tighten: Tighten all connections snugly. Avoid overtightening.

Regularly check seals and reapply putty or caulk over time as needed. Catching minor leaks early prevents big headaches!

Proper Venting Helps Avoids Clogs

Venting the tub drain allows air flow to prevent vacuum lock and gurgling drains. Here are some key vent line tips:

• Run the vent vertically to tie into main vent stack.

• Connect at least 4 to 6 inches above drain pipe.

• Avoid horizontal runs or dips that can collect water.

• Use minimum 1 1⁄2 to 2 inch pipe for vent.

• Insulate vent pipes in cold climates to reduce condensation buildup.

Proper drainage relies on an adequately sized and sloped vent line. Don‘t skip this crucial step!

Rough In Dimensions for Different Bathtub Types

Beyond the general guidelines, drain positions and sizes vary based on the specific style of bathtub:

Alcove Tubs

• Drain hole centered 12-14 inches from wall.

• Drain height 6 1⁄2 to 8 inches above floor.

• Hole diameter typically 5 1⁄2 inches.

Freestanding Tubs

• Drain 2 to 5 inches from outer tub edge.

• Drain height level with floor.

• Drain hole often 3 inches across.

Drop-In Tubs

• Drain 12-16 inches from tub rim.

• Drain height 1 1⁄4 to 2 inches below deck.

• Drain hole 2 inch diameter.

Corner Tubs

• Drain hole 8 to 12 inches from rear wall.

• 12-16 inches from tub edge.

• Hole is usually 5 1⁄2 inches in diameter.

I hope this outline gives you a great starting point for mapping out your tub drain rough in. Don‘t hesitate to reach out with any other questions!

Bill E. Plumber
Tub Drain Pro