ADU bathroom design and floor plan: best practices

How To Design The Best ADU Bathroom

7min read
by Olesia Chikunova, ADU Specialist.

Bathrooms are one of the most highly-trafficked rooms of a home. From being a place where you prepare for the day or wash off the exhaustion of a tiring schedule to a room where you treat yourself with an occasional spa time, bathrooms play a significant role in our everyday routines. 

We have recently covered in detail all the features of a small home.  We have even studied Frank Lloyd Wright designs to borrow his genius ideas to make smaller homes feel big.

Today, let us pay special attention to a bathroom.

A junior accessory dwelling unit may use one of the bathrooms in the main home, so can a garage conversion permitted as a junior ADU. However, suppose you are applying for a standard ADU building permit. In that case, you must follow state law and local regulations and demonstrate proper bathroom facilities. Even if that ADU space is just 150 square feet, a minimum size for an ADU plan.


Secondary dwelling units are promoted as affordable housing solution – be it as a guest house for family members or as a source of rental income. It is required to have a fully functioning own kitchen – be it a full kitchen or an efficiency kitchen. ADU’s design should also demonstrate its own bathroom. 


But this doesn’t mean you have to own a luxurious bathroom to make things fancy and enjoyable. With the right floor plan, design, and decor, even a small bathroom (like the ones in the best ADU homes) can be a peaceful and lovely oasis that you’ll look forward to spending time in. 

So without further ado, let’s jump in to unfold the smartest floor plans and designs for a small bathroom to help you create a calming retreat right in the comfort of your secondary dwelling unit! 

Types of Layouts for Small ADU Bathrooms

traditional ADU bathroom in blue

While there are countless different layouts for bathrooms, picking out an option that perfectly suits your requirements, lifestyle, and available square footage is challenging. 

Below we’ve rounded up a list of the top ADU bathroom layouts for small spaces to help you pick the best choice for you. 

Full Bath

A full bathroom includes a bathtub, shower, toilet, and sink. You can either go for a center or side bathroom layout. Centre layouts are designed to have two fixtures on each wall, with the toilet and sink paired on one and the shower and tub on the other.

On the other hand, side layouts have all the fixtures installed on one side. The latter is a better option if you have a small bathroom. This is because side layouts have a narrow floor plan and lower construction costs since all the plumbing fixtures are installed on one side. 


modern ADU bathroom


¾ Bath 

A three-quarter bath contains three of the four fixtures, including the sink, toilet, and tub OR shower. When designing a small space, homeowners often choose this option and prefer the shower over the tub — especially in the US, where people like showering more than bathing. ¾ baths are also easier to clean, making them a good choice for ADU homes. 


towel warmer in a bathroom


Half Bath

Also called powder rooms or utility bathrooms, a half bath typically includes only the sink and the toilet. Depending on how you want these fixtures to be installed, you can decide accordingly with either a single wall, linear, or split design layout.

Half baths are a good option for the bathrooms near the guest room or the kitchen. If you’ve got an ADU home that you’ll be renting out for passive income, we’d suggest opting for a full bath or at least a ¾ bath. However, if you have a two-bedroom ADU in the plans, please consider adding a half bath by the living room. You can tuck in a washer there – a feature any renter will truly appreciate.


washing machine in a toilet

Wet Room 

A wet room is a wholly tanked bathroom with the shower area installed on the same level as the rest of the bathroom. Since the walls and floors are fully waterproofed with appropriate materials, the risk of runaway water causing any damage to the interior is eliminated. Moreover, this bathroom floor plan does not require an enclosure around the shower area. But you can always set up glass screens to keep the rest of the bathroom dry while showering. 

If you’re designing a rental ADU, a wet room as an ADU bathroom will expand your target market. This is because wet rooms are ideal for people with mobility issues, which means guests who use a wheelchair or want to avoid climbing into the shower or tub will also be attracted. Remember, wet rooms do not have obstructive walls, creating the illusion of a bigger space in your small bathroom. 

ADA bathroom

Typical Mistakes To Avoid In ADU Bathroom Planning

Your bathroom design needs to be planned carefully, especially if you already have limited space. Here are a few common mistakes you should avoid. 

  1. Installing swinging doors for the shower. A small bathroom means a small shower cubicle. If you have a door that swings inwards, you’ll struggle when coming out of the shower. While if the door swings outwards, it will take up space inside the bathroom itself and allow water to come out of the cubicle after you’ve showered. Solution: Do not use swinging doors, use frameless siders or bypass doors. 
  2. Overlooking proper fixture placement. Installing fixtures without appropriate planning or close attention may result in an impractical and cramped bathroom. Solution: Place the shower and/or toilet in a separate closet and keep the sink away from them. This will increase privacy and double the functionality by allowing more than one person to use the bathroom simultaneously. 
  3. Cutting corners on storage space. Without good storage, the bathroom will always appear cluttered and suffocating. Solution: Look up organization and storage hacks for small bathrooms, such as niches, floating shelves, under-the-sink baskets, medicine cabinets, over-toilet cabinets, behind-the-door organizers, etc., to make sure the bathroom looks sleek and clean at all times. This will also be a great addition to your ADU, as guests will love the idea of an organized and immaculate space. 
  4. Installing insufficient lighting. An inadequately-lit bathroom is a huge turnoff. The proper lighting sets the mood and uplifts the interior dramatically. Solution: Install layered lighting, including task, ambient, and accent; maximize the window sizes, and lighten the window coverings. Such additions will also make a small bathroom look much bigger and airy. 


ADU Bathroom Requirements & Key Features 

Now that you’re familiar with the layouts for small bathrooms and the mistakes to avoid, we’ll move on with the specific requirements and key features of ADU bathrooms. 

An ADU bathroom in California must be at least 30 square feet with a minimum of a ¾ bath. You can also offer separate sanitation facilities or level up the bathroom to a full bath if you have enough space.

Remember that building codes drive some requirements inside the bathroom – and they are the same as for a primary dwelling unit. Ensure sufficient space is in front of the sink, on both sides and in front of the toilet. There are requirements for the size of the shower AND shower door.

Energy efficiency requirements call for a heat pump water heater – remember to plan for its location before submitting your permit application. It needs to be reflected in your ADU design.

If your property allows, you can even add more than one bathroom. The best part? After providing one full or ¾ Bath, you can proceed with a half bath attached to the kitchen or any other area, too. Not to forget, this will add drastic value to your property! The maximum size of an ADU is 1200 sq ft. You can fit in a full bath and ¾ Bath plus an in-unit washer. 


Once the layout has been decided, it is time to select appropriate key features. Choose between a shower and a tub, pick the suitable tiling material, decide if you want a double or single vanity, install maximum storage, and purchase the lighting and mirrors to expand the space visually.

Pro tip: save an outlet for new towel racks. And consider a heated floor – nothing spells luxury as standing barefoot on warm tiles.


Choosing The Best Interior Design Style For A Small ADU Bathroom

Design styles significantly impact how a bathroom feels and looks. A modern design, for example, uses light colors, clean lines, and smooth surfaces — all critical elements of a visually brighter and bigger space. It keeps things calm and clean, which gives the vibe of an airy and spacious bathroom.

Features of a traditional design, including built-in cabinets, sophisticated small vases, and flowing linen shower curtains over French doors, all contribute to designing a small bathroom space-efficiently. Similarly, Scandinavian bathrooms have multifunctional and flexible designs, a minimalistic aesthetic, and bright, light-filled spaces. 

Remember, whichever design style you opt for, the key is to skim out and design with all the features and aspects that suit a small bathroom and make it look visually bigger and airier. 

Spending some “me time” in the bathroom can always uplift your mood, regardless of the bathroom size. What matters the most is the floor plan and decor of the bathroom. So, what are you waiting for? Use our guide, pick the layout that suits your requirements, and start decorating with your favorite design style now!

Not ready? Follow us on Pinterest for more ideas.

spa bathroom

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