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How to add a bathroom addition to your house

There are plenty of good reasons to add an extra bathroom to your home. Whether it be for convenience or property value, a bathroom addition can be a worthwhile investment when done correctly. So how do you add a bathroom to an existing home? The answer may not be as simple as you think.

The process of installing a new bathroom is a technically complicated process that requires extensive design work. At Lamont Bros., we’ve worked with many Portland-area homeowners to design and install new bathrooms for their homes. Although it’s never an easy process to add a bathroom, it can be very rewarding for your lifestyle and your home’s value in the end. 

This article covers everything you need to know about adding a bathroom to your home. You’ll be able to read about the benefits and challenges of these types of remodel projects. We’ll also discuss the cost range and process so you know exactly what to expect. Specifically, you’ll be able to read about:

Why add a bathroom to your home?

There are plenty of reasons why somebody might choose to add a bathroom. The need for a new bathroom can be the result of several factors, but the most common ones are listed below. 

Lifestyle Changes

A home with two bathrooms might have been enough for a small family when the kids were young. But as the same family grows in numbers or age, they find two bathrooms just don’t cut it.

It’s normal for growing families to find that they need more bathrooms. At first, it’s because they have more children, and more children means more bathrooms. Then, as the kids grow up and need to shower more regularly, arguments over bathroom time become more common. The needs of a bathroom tend to evolve over time. This applies to the number of bathrooms and their functionality. 

Other times, it’s aging or a mobility restriction that necessitates a new bathroom. When a member of the family has a difficult time getting around, it’s important to have a bathroom on every level of the home for ease of access. 

Many bathroom remodels aim to solve issues related to “aging in place.” This is based on the principle that a person’s bathroom needs to change as they enter their senior years. The goal of an aging-in-place bathroom remodel is to make it possible for an elderly person to function in their own home for as long as possible. Amenities for aging in place might include grab bars on the wall, curbless shower floors to reduce trip hazards, and ensuring there is at least one bathroom for every floor.

Home Layout

Sometimes, a homeowner may choose to add a bathroom addition to their home because their current layout doesn’t meet their needs. For example, a person living in a 1-bathroom home who regularly entertains guests may want an additional powder bathroom for company to use. Other times, a homeowner may want to add a master bathroom to a home that doesn’t have one. 

Older homes are especially known for having fewer bathrooms located in unusual places. In many homes built during the early 20th century, you’ll only find one bathroom. This was true, even in multi-level, 3-4 bedroom houses.  For people living in these homes, needing to add a bathroom (or several) is almost inevitable. 

Property Value

Of course, having an additional bathroom in your home is a great way to increase its value, as well. Bathrooms count every water utility (sink, toilet, shower, bathtub) as a “quarter-bath.” So, a half-bath (AKA powder room) has a sink and a toilet. A ¾ bath has a sink, toilet, and shower.

When calculating the value a bathroom adds to a home, a general rule of thumb is 5% for every water utility. So a half-bath will increase the value of the home by 10%, while a full bath is closer to 20%.

It’s important to keep in mind that it often takes time for a remodel to pay off as an investment. However, the longer you wait to sell your home after remodeling, the more money a renovation will make you. You can learn more about how much value a remodel adds to your home using our remodel investment calculator

What is the process to add a bathroom?

The process of adding a bathroom to a home varies from case to case. What they all have in common is that at the end of the project, there will be a bathroom where there wasn’t before. The specifics of how you arrive at that goal depend largely on your needs as a homeowner.


When you add a bathroom to your home, the first step is to design it. For bathroom additions especially, this is a very important part of the process. A well-designed bathroom addition will ensure that your new bathroom is functional, serves your needs, and meets construction regulations. 

Bathroom layout

You’ll need to figure out what type of bathroom you want. Which utilities do you need in the new space? In other words, will this be a full bath, half bath, or somewhere in between? One great way to decide this is by establishing who will be using this bathroom the most. 

Is it the homeowner? If so, you’re probably looking for a master bathroom with all the bells and whistles. Is it house guests? Then a powder bathroom with a sink and toilet will do nicely. Is it your teenage kids? In that case, a Jack-and-Jill bathroom with two sinks and a separate toilet/shower closet may be the best option.

Bathroom location

Once you know what type of bathroom you want, the other design issue you’ll need to solve is where the bathroom will go. This is often the trickiest part of the process. There are two options to choose from when you add a bathroom to your home.

The first option is to renovate the existing space in your home into a bathroom. Sometimes, a large closet can work for this purpose. However, most of the time, you’ll need to build a new room somewhere in your home. This typically involves adding several new walls and repurposing other living spaces — often a bedroom. 

When a home has limited space to begin with, it can be difficult or impossible to add a bathroom to the existing floor plan. The alternative is to do a proper addition and install a bathroom in it. In this type of project, the bathroom adds to the house rather than takes up existing space. While this option offers more design flexibility and adds more value, it is typically more expensive.


The time it takes to add a bathroom to your home typically ranges between 6-12 weeks. This timeline includes approximately 4-5 weeks of design and architectural planning. 

Ultimately, your remodel’s timeline comes down to the scope of work and the ease with which the build team can complete the work.  The more complex the project and the more fine detail work required, the longer you can expect it to take. 

A simple powder bathroom with minimal tile work would likely take 6-8 weeks. On the other hand, adding a brand new master bathroom with a custom tile shower would fall closer to the 10-12 week timeline. 


In the world of remodeling, a bathroom addition is one of the most technically complicated projects out there. 


Plumbing presents the greatest challenge when you add a bathroom to your home. The reason has to do with the order in which a house is usually built. For new homes, the bathroom utilities typically get installed after framing but before HVAC, electrical, drywall, or finish carpentry.  This is because it’s much easier to install everything else around the pipes than it is to install the pipes through finished construction later. When you add a bathroom, the latter is exactly what you end up doing. 

Adding or rearranging plumbing lines can drastically add to a bathroom addition’s cost.

Typically, the closer you build a new bathroom to an existing set of water supply and waste lines, the easier the process will be. It’s much less complicated and less expensive to run these utilities a few feet into the wall rather than across the house. While it is possible to add a bathroom farther away from the existing plumbing, this requires extensive labor hours and quickly drives up the cost of a remodel. 

Another challenge when adding a bathroom is the capacity of your supply and drainage lines. A single water or sewer pipe can only handle so much flow. For example, a 3-inch sewer line can only connect to 3 toilets before requiring additional drainage. Adding water utilities may also require that you upgrade your water meter. To determine whether your bathroom addition will require this type of plumbing work, use this worksheet from the City of Portland.


Another challenge you’ll face when installing a new bathroom is re-wiring your electrical circuits. By law, every bathroom must be on its own ground-fault circuit. You’ll also likely need a new circuit for the lighting, and another dedicated circuit for any high-voltage utilities, such as a hairdryer or curling iron. Fan heaters, heated floors, and jetted tubs need their own circuits, too. 

Similar to plumbers, electricians are high-cost contractors. Unfortunately, when adding a bathroom, electrical work isn’t optional. Expect to spend more money for every circuit you add to your bathroom. If your goal is to save on cost, stick with the essentials. 


You’ll also need to consider how the demolition phase of the project will affect the rest of your home. To install a new bathroom, your build team will need to prepare the space for it to go in. This means demolishing whatever was there before. It also means making room to work on the plumbing lines, which may involve tearing up several feet of flooring to access it. 

You and your design team should discuss the changes that will need to take place to install the new bathroom. While your contractor should return the rest of your home to the condition it was in before the remodel, the work zone may affect areas outside of the new bathroom during construction.

How much does it cost to add a bathroom?

Because the project requires such extensive changes to the structure and plumbing of a home, you can expect to pay at least $65,000 to add a bathroom. The larger or more complicated you want your new bathroom to be, the more expensive it gets.  For bathroom additions, the two factors that most directly impact the cost are its size and the finishes you select. 


The size of a bathroom addition has a direct effect on the cost. After all, the bigger the bathroom, the more space in your existing home has to be turned into a bathroom. Size also influences the cost because larger bathrooms also tend to be more complex — because they have room to be. 

A simple half-bath powder room addition with a toilet and sink will cost between $60,000 – 90,000. Add a shower-tub combo to make it a full bath and you’ll probably spend $85,000 to $110,000. If you’re looking for a full master bath remodel, you could spend well over $100,000. It all depends on how much space you want and what features you have to have.


The cost of finishes can also impact your final bill. Luxury-level countertops, lighting, and plumbing fixtures can increase your costs substantially. 

Plumbing fixtures might not immediately come to mind when you think of big purchase items for a remodel.  However, even a high-quality set of faucets for your bathroom can cost several hundred dollars. Because the cost of new sinks, shower heads, and faucets can add up quickly, it’s important to budget carefully when selecting your plumbing fixtures

The cost of adding tile to a bathroom is mostly affected by labor hours.

Then there’s the issue of tile. Although the material itself doesn’t usually cost a lot, the installation does. Tile setting requires careful attention to detail and many hours of labor. So much so that a tile shower alone can increase the cost of a bathroom remodel by $10,000-15,000.

You can learn more about the cost of bathroom remodeling by reading our article, “How much does it cost to remodel a bathroom in Portland?

Ready to start designing your bathroom addition?

Now that you know more about how to add a bathroom addition, take the next step! Check out our Bathroom Remodel Portfolio, where you can learn more about bathroom remodeling and start gathering ideas and inspiration for your own remodel.

Are you ready to talk with a professional design team? If so, click the button below to schedule a free video consultation with one of our design consultants. We’ll help you get a better understanding of the remodeling process and help you turn your current home into your dream home.