Tips & Guidance on Adding a Bathroom to Your Garage

Recently, homeowners have been looking for ways to get the most out of their spaces. For many, this means renovating the garage to eke out some extra square footage — and with good reason. Dreaming of a decked-out home office? Gym? Workshop? Guest suite? The possibilities are endless.

And if you’re creating a space you or your loved ones will be spending a lot of time in, you’ll want to go the extra mile to make it as comfortable and convenient as possible. In most instances, that means adding a bathroom. 

Whether you’re creating a full bathroom complete with shower, sink, and toilet, or a simple half bath, building a garage bathroom is a complicated process. That’s in large part to structural considerations as well as updates to your plumbing and electrical systems. But with an experienced contractor well-versed in the intricacies of design and construction in Los Angeles and Southern California, you’ll have the lights on and the water running in no time. These tips will help you start the planning process for adding a bathroom to a garage

Here at GreatBuildz, a free service that connects homeowners in Los Angeles, Orange, Ventura, and San Diego Counties with reliable contractors, we speak to homeowners every day about planning their desired remodel to ensure a strong return on investment – here are some ideas & tips to get you started.

Check local laws and secure necessary permits

Adding a Bathroom to Your Garage Permits

Many municipalities and HOAs dictate specifications on the building of living spaces in garages. For example, some zoning laws don’t allow homeowners to park their vehicles on the street. If your plans for using your garage post-renovation mean you’ll no longer be parking your car in your garage, you may also have to consider the addition of a carport or other parking solution. So before you get started on adding a bathroom, consult a local building inspector on any laws affecting your project. 

Additionally, many building codes require homeowners to secure permits and other relevant approvals before they can start any major home improvement project. Failure to do so can lead to fines and other penalties — such as requiring the homeowner to adjust or even dismantle new construction at their own expense.

Some contractors will dissuade you from getting city permits. They will tell you that they can do it faster and cheaper without a city permit. And in some regard, that is true because it will save you the time and expense of having city inspectors review the project on several occasions.  However, this idea is not advisable for several reasons. First, your city’s laws most likely require a permit for this project. Second, if a project like this is done without permits, you may have issues when you go to sell the house and disclose that this bathroom is unpermitted. And finally, without city inspectors checking on the quality of the job, you could find that your contractor performed shoddy work that wont last.  

Look into your garage’s plumbing and electrical systems

Once you’ve got the green light for building a garage bathroom, it’s time to call a general contractor to evaluate your home’s existing plumbing system and water heater capabilities. In some instances, it will be possible to draw water from your existing system to your new bathroom by running pipes underground or in your walls. If it’s not possible, your contractor should be able to make recommendations on adding a bathroom plumbing system to your garage.

Keep in mind that the water ‘supply’ lines are the easier part to run for your new garage bathroom. The more challenging (and expensive) part is the waste-lines (sewer lines) that will have to be located under the toilet/shower and routed to connect with existing waste-lines. Your contractor or plumber will have the needed tools to locate the nearest waste-lines to connect to.

Meanwhile, they’ll also be able to advise you on the best locations for new wiring and outlets for your garage bathroom. Its likely that your garage already has electrical systems in place, so the contractor will be able to use those to provide outlets and lights to your bathroom.

Don’t overlook the ventilation system

When building a garage bathroom, it’s important to ensure there’s an adequate ventilation system to prevent steam and moisture from building up in your space. This often entails installing a window — usually 1.5 square feet or more – to facilitate airflow, as well as installing vents in the ceiling to improve circulation. Or you’ll need an exhaust fan and ducting out through the roof or wall.

Your paint job can play a role in ventilation as well. Moisture-resistant, glossy enamel will deter the formation of mole and mildew, and it’s easy to clean as well. 

Planning the bathroom layout

Using the insight from the site visit, your contractor will start drafting possible layouts for your garage bathroom.

Most regions require construction projects to adhere to guidelines outlined by the International Residential Code, and individual states and municipalities have their own regulations as well. The International Code Council has an interactive database of building codes for each state, which includes separate standards for the City of Los Angeles and the County of Los Angeles

Bringing together form and function

Adding a Bathroom to Your Garage Function & Form

The planning process isn’t all work and no play. This is the time to visualize the space you want and start exploring design elements like key features and fixtures. And when it comes to what you can include, the sky’s the limit. 

Some of the top trends in bathroom design include tech integration like heated floors, smart toilets, and touchless faucets; universal design elements such curbless shower entries and shower seats; and spa-like features like rainfall showerheads, mood lighting, and skylights. 

An interior designer with expertise in bathroom renovations can work hand-in-hand with your contractor to ensure the end result is beautiful and built to last. The goal when adding a bathroom like this is the perfect marriage between form and function.

How to add a bathroom to a detached garage

If you have a detached garage, you’ll likely have a more time-consuming — and yes, expensive — project than those with attached garages. Since the structure is not only disconnected but also typically some distance from the home, the added cost largely comes from extending the existing utilities (plumbing & electrical) to the new space, as well as piping for drainage that can take wastewater to the sewage system. 

Sometimes it may not be the best option to direct the plumbing from your home to the detached garage. For example, there may be a water point outside the house used for watering the yard that would be easier (and closer) to connect to. 

That being said, given the spaciousness and versatility of a detached garage, it could be very well worth it!

Find a Good Bathroom Contractor

Adding a bathroom to a garage requires the services of a licensed General Contractor (B-license). Only this category of contractor is legally permitted to undertake this type of project requiring a variety of trades (ie. electrician, plumber, carpenter, etc). If you are interested in adding a bathroom to your garage, you should contact a licensed general contractor. Meeting with one or more contractors will provide you with a rough understanding of the reality and estimated cost of your proposed job. Make sure that any legitimate contractor you’re considering for this project has an active general contractor’s license (CSLB) and can provide you with evidence of their workers compensation and general liability insurance.

Total costs to add a bathroom to a garage

Adding a Bathroom to Your Garage White Bath

If everything regarding existing plumbing and electricity falls into place, you can expect adding a bathroom to a garage to cost about $30k. If your specific situation is a bit more complex and/or if you’re considering using higher-end finish materials and fixtures, your bathroom addition may cost closer to $50k-$60k. Keep in mind the following cost categories when planning a garage bathroom: plumbing, electrical, lights, drywall, insulation, paint, tub/shower, toilet, vanity, flooring, tile, & fixtures. It may be wise to produce your own bathroom scope checklist to hand to contractors so everyone is on the same page as to the extent of the project.

One of the biggest costs of a new bathroom in your garage is connecting the toilet, sink, and shower to the waste lines of the home. This requires digging through a foundation or opening the subfloor and finding the closest connection to the existing wastewater system. Another major cost is running the plumbing supply lines (both hot and cold water pipes) from the nearest point as well. And most people overlook that a new bathroom will require a vertical vent line that must be run through the roof. So clearly the further the garage is from the home, the more expensive are costs for running all the plumbing lines.

There is no way to know your exact project cost without getting contractor bids. All the research online wont be able to peg your specific cost because every situation is unique and different. Its always a good idea to get three contractor bids for any large project such as this. You may be surprised to find that contractor estimates can vary widely (which is often difficult to understand). If you get three bids that are all similar in cost, within 10-20% of each other, you can confidently choose from one of these. If your bids are all over the place, with some way higher or lower than average, you might seek more contractor bids. Some people are nervous to accept both the highest and lowest bid, and might opt for the price in the middle.

How long does it take to build a garage bathroom?

Depending on the complexity of your bathroom addition and where the property is located, you may be required to develop plans for the project. This will require hiring an architect, however, a good contractor can typically bring in their preferred team. Deciding on your preferred floor plan, developing the plans, and getting the necessary approval through your building department’s plan check process will typically take a month or two. 

Once plans are approved and you have the permits in hand, you’re ready to start construction. For a seamless, attached garage bathroom addition, you can expect construction to take about 4-6 weeks. If there is trenching involved or if there are any other complications, your project may take up to 2+ months to complete.

When it comes to remodeling for your home, you shouldn’t have to go it alone – GreatBuildz can help simplify your renovation experience.



GreatBuildz is a free service that connects homeowners in Los Angeles, Orange County, Ventura or San Diego with reliable, thoroughly screened general contractors and provides project support from start to finish. Call now (818.317.3567) to chat with a real person about your next remodel project or visit our website for more information:

Hi, we're Paul and Jon - Co-Founders of GreatBuildz. We believe everyone deserves to find a great contractor, have a stress-free renovation, and enjoy their beautiful new space. There are so many contractors out there and it's often hard to tell the good from the bad... until it's too late. We started our company to help simplify your contractor search and help you have a stress-free renovation experience. We're always available to help, no matter where you are in the process. Click here to learn more about our story.

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