How To Install a Basement Bathroom

Installing a basement bathroom can significantly increase your home’s value and functionality, but it’s a big project. In the video above, This Old House plumbing and heating expert Richard Trethewey demonstrates the key steps and considerations for the new plumbing you’ll need to install. In this article, we’ll guide you through the process of roughing in the drain pipes for a basement bathroom, a crucial first step in the installation.

Can I Install My Own Basement Bathroom?

While parts of bathroom construction are DIY-friendly, only a licensed plumber should install new plumbing. In the video above, expert Trethewey seeks out help from a licensed plumber. These trained professionals are already familiar with local building codes and necessary permits. 

Hiring a licensed plumber will also ensure that your new bathroom increases your home’s value. Plumbing that isn’t up to code can cause serious problems during the appraisal and sale process, so don’t risk it by trying to do the whole job yourself. Once the plumbing is in place, you can start work on your new bathroom. 

Below, we’ll outline the installation process from preparation to finishing and note the steps that a DIY-savvy homeowner can take.

Planning Your Basement Bathroom

Before diving into the installation process, and even before calling a plumber, plan your basement bathroom layout carefully. Consider the following factors:

• Available space: Measure the available area in your basement to determine the best layout for your bathroom. Allow enough space for all fixtures while maintaining comfortable movement and accessibility.
• Desired fixtures (toilet, shower, sink): Decide on the type and size of fixtures you want in your bathroom. Consider the space available and your personal preferences when selecting a toilet, shower, and sink that will fit comfortably in the layout.
• Existing plumbing connections: Assess the location of existing plumbing lines to simplify installation and minimize the need for extensive plumbing work. Aligning your bathroom fixtures with existing connections can save both time and money.
• Local building codes: Familiarize yourself with local building codes and regulations to ensure your basement bathroom is up to code. This may include requirements for plumbing, ventilation, electrical work, and egress windows.

Assessing Existing Plumbing

Examine your basement’s current plumbing setup to determine the best way to connect your new bathroom’s fixtures. Locate the main drain lines, vent stacks, and water supply lines. If you can work around existing elements instead of moving them, installation will be more efficient and less expensive. Also, ensure you know the capacity of your existing system to handle additional fixtures.

Obtaining Necessary Permits

Check with your local building department to obtain the required permits. This step is crucial to ensure your installation meets all local codes and regulations. A licensed plumber will take this step as part of the process.

Choosing Fixtures and Materials

Here’s where you can personalize your new basement bathroom. Select fixtures that fit your space and aesthetic preferences. Common basement bathroom fixtures include compact toilets, corner sinks, and shower stalls that optimize space. Using moisture-resistant materials will prevent water damage in a space prone to high humidity.

Step 1: Preparing the Basement for Installation

Once you have your plan in place and permits secured, it’s time to prepare the basement area for installation. You may be able to do some of these preliminary steps yourself.

Laying Out Wall Plates

Begin by laying out the 2×4 bottom wall plates to establish the perimeter of your bathroom walls. This helps visualize the space and ensures accurate placement of fixtures. Use a chalk line to mark the positions of the plates on the floor, then move them out of the way.

Exposing the Existing Plumbing

In the video above, the concrete flooring in the new bathroom location has already been removed, and the existing drain pipe has been exposed. However, if your basement is finished, you’ll likely need to hire a contractor to break up and dispose of the concrete.

Marking Fixture Locations

With the wall plates in place, measure and mark the center locations for the shower drain and toilet flange. These marks will guide your plumbing installation. Use a tape measure and level to ensure precise measurements.

Excavating for Plumbing

Following your markings, dig trenches for the new plumbing lines. Extend these trenches from the existing drain pipe to the marked locations for the shower drain and toilet flange. The depth and width of the trenches will depend on your local building codes and the size of the pipes you’re using. 

As you dig, work carefully around any obstructions, such as existing pipes, electrical wires, or ductwork. You don’t want to accidentally jam your shovel through a buried pipe. Adjust your layout as needed to navigate these obstacles.

Step 2: Installing the Drain Pipes for the Basement Bathroom

With the space prepared, a licensed plumber can now begin installing the drain pipes for your new basement bathroom. You can work with your plumber to ensure that the new fixtures meet your design plans.

Connecting to Existing Plumbing

In the video above, Trethewey connects the new plumbing to the existing system with the following steps:

1. Use a right-angle grinder with a diamond-impregnated cutting wheel to cut through the old cast-iron drainpipe.
2. Attach a flexible no-hub mechanical coupling to the cut end of the drainpipe.
3. Tighten the hose clamp onto the cast-iron pipe using a torque wrench to ensure a secure connection.

Your drain pipe may be located in a different place or made of another material. A licensed plumber can create a leak-free connection to existing pipes.

Installing PVC Drain Pipes

The size of pipes you need will vary by local building code, but these are the general steps a plumber will take when installing basement bathroom drain pipes:

1. Cut and glue together 3-inch-diameter PVC pipes and fittings to form the main drainpipe assembly.
2. Connect this assembly to the old cast-iron pipe using the mechanical coupling.
3. Run 2-inch-diameter PVC pipe from the main assembly to the shower and vanity sink locations.
4. Ensure all pipes have the proper slope (1/8-inch per foot) to allow for proper drainage. 

Setting Traps and Vents

As part of the process, a plumber will install traps on each fixture to prevent sewer gasses from entering your home. They’ll also ensure proper venting for each fixture to maintain drainage and prevent air locks. Your local plumbing code will dictate specific requirements for traps and vents. The plumber should test the system for proper function before sealing.

Step 3: Securing and Protecting the Bathroom Plumbing Installation

Before pouring the concrete floor, the plumber will take steps to secure and protect the newly installed plumbing.

Stabilizing Pipes

One method of keeping new pipes in place is to drive 1/2-inch-diameter steel-reinforcing bars into the soil beside each trap. Duct tape can secure the bars to the traps, preventing movement and maintaining accurate drainage slopes during the concrete pour.

Protecting Open Pipes

The plumber may cover the open end of the toilet pipe with a foam cap and wrap plastic around the shower drain pipe. This precaution prevents concrete from entering the pipes during the floor pour. 

Insulating Pipes

If you live in a cold climate, now is the time to insulate your water supply lines to prevent freezing. Insulating will also reduce energy costs by retaining heat. Talk to your plumber about the best insulation options for this project.

Step 4: Final Plumbing Inspection and Concrete Pour

Even if it’s laid by a licensed plumber, the rough plumbing may need to be inspected by a local building inspector before pouring the concrete floor. Your plumber should promptly address any issues identified in the inspection. 

Once approved, proceed with having a concrete contractor pour the new floor around your plumbing installation. Make sure the floor is level and smooth to facilitate the installation of floor coverings and fixtures.

Step 5: Finishing the Basement Bathroom

With the rough plumbing completed and encapsulated in concrete, move on to finishing the basement bathroom. Here are the major tasks you’ll typically need to complete:

• Build the new stud walls using moisture-resistant drywall or cement board: Construct the walls of your bathroom using materials specifically designed to withstand moisture. This is crucial in a basement environment to prevent mold and mildew.
• Waterproof tub and shower surrounds: Waterproof the areas around the tub and shower to prevent water from seeping into the walls and causing long-term damage.
• Hire an electrician to run electrical wiring: Ensure that all electrical work is safely completed by a licensed electrician, including wiring for lighting, outlets, and necessary ventilation systems.
• Install new fixtures: Carefully install each fixture, including the toilet, shower, and sink, making sure they are securely connected to plumbing and properly sealed to prevent leaks.
• Paint finished walls with mildew-resistant paint: Apply a mildew-resistant paint to protect the walls from dampness and potential mold growth, which is common in basement environments.
• Install flooring that withstand moisture: Choose and install moisture-resistant flooring that’s durable and suitable for the often humid conditions of a basement bathroom.
• Add any final touches: Finish the bathroom with decorative and functional touches that enhance the space, such as mirrors, shelves, and other accessories.

Our Conclusion

Installing a basement bathroom is a complex but rewarding renovation that can substantially enhance your home’s value. You can do some of the preparation and finishing work yourself, but you’ll need to hire a licensed plumber to ensure the new bathroom is up to code. You’ll also need a licensed electrician, so some homeowners opt to hire a general contractor to coordinate the project. Whether you choose to take charge of the renovation or hire help, we recommend choosing quality, water-resistant materials to get the most out of your investment.