The Case for Bathroom Insulation (And When It’s Not Necessary)

My partner likes to take long showers (I’m talking 45 minutes+) which often means that even with the fan running our mirror is fogged and our walls are damp long after he exits the bathroom. This was all fine and dandy until we started noticing little black splotches on our ceiling… particularly right above the shower. No matter how hard we tried to clean and bleach them away, the mold kept coming, forming a distinct rectangle on our ceiling. We decided to investigate and discovered that the rectangle was a drywall patch placed over what must have once been a chimney vent in our 1900s home—basically, an uninsulated hole that went straight to our roof. Safe to say it’s now properly insulated, drywalled, and repainted, and we haven’t seen a spot since!

Steamy bathroom, wood counter with white bowl sink

There are a lot of reasons you might consider insulating bathroom walls in your home; mold and mildew prevention being one of them. But there are also cases where bathroom insulation isn’t necessary. We’ll cover all the incentives for bathroom wall insulation, when you can skip it, and how to choose and install the right insulation for your home and climate.

6 Reasons to Install Bathroom Insulation

  1. Moisture Control: As my partner clearly demonstrates, bathrooms are prone to high humidity, which can lead to condensation within walls and eventually to mold and mildew growth. And it might not always be as visually apparent as it was in our bathroom. In fact, the hidden damage mold, mildew, and rot can do to your home’s framing is worse than the spots on your paint. If left untended, you can end up with structural damage and costly/disruptive repairs. Proper bathroom insulation can prevent moisture from penetrating walls and causing these issues and improve your indoor air quality.
  2. Temperature Regulation: It’s no fun to step out of a luxurious, hot shower and immediately find goosebumps on your skin because your bathroom is cold. Likewise, a cold shower does little good in summer if your bathroom is sticky and hot. Bathroom wall insulation, especially for any exterior facing walls, can help maintain a comfortable and consistent temperature.
  3. Energy Efficiency: Your bathroom may be a small portion of your home’s overall footprint, but if it has exterior walls lacking high-quality insulation, it may be a source of energy loss. Increase your home energy efficiency and save on heating and cooling costs by adding appropriate bathroom wall insulation.
  4. Noise Reduction: Say your bathroom shares a wall with a bedroom or common area like your living room—the sounds of the toilet flushing or the shower running aren’t exactly conducive to creating peaceful and private spaces. One of the biggest benefits (and most common motivations) of bathroom insulation is its ability to reduce noise.
  5. Protect Plumbing: If you live in a colder climate, lack of bathroom insulation bears the risk of pipes freezing, which can burst and lead to extensive water damage. Keeping your bathroom temperature regulated with proper insulation also has the benefit of protecting your plumbing.
  6. Take Advantage of Renovation: In 2020, bathroom remodels made up 30% of total home renovations and homeowners are setting increasing budgets for their bathroom makeovers. So, if you’re planning to revamp your bathroom, you’re not alone. Not only is this a convenient time to add bathroom wall insulation, but it may also be necessary to comply with building codes. Check your local state and city regulations to find out if insulating bathroom walls is a requirement for your remodel project.

When is Bathroom Insulation Not Necessary?

We can sing the praises of proper insulation but it’s important to note that insulating bathroom walls isn’t always necessary or practical. If your bathroom is located within your home’s conditioned space and only shares walls with other interior rooms, bathroom insulation may not be a top priority. If your bathroom is already surrounded by heated or cooled spaces, you can likely skip this insulation project. In some cases, you may still decide to insulate bathroom walls for soundproofing.

No matter what, you should always consider important factors like your local climate and the specific construction of your walls before choosing to insulate.

How to Insulate a Bathroom

If you’ve made it this far, that probably means you’d like to add bathroom insulation and want to know how! For competent DIYers, insulating bathroom walls is a manageable project to take on without professional assistance. Start by choosing the best bathroom insulation for the job.

bathroom walls stripped to studs

Historically, spray foam has been a popular choice of bathroom insulation as it is water-resistant and good for sealing drafts, but it requires professional equipment to be installed properly. For DIY bathroom wall insulation, rigid polystyrene foam sheets are easy to install. Unfortunately, the manufacturing of foam boards releases dangerous hydrocarbons into the air which can contribute to global warming and be hazardous to human health.

Wood fiber insulation is a great alternative, being equally safe and easy to install with the added benefit of arriving at your home carbon negative. This new insulation technology is made from the wood waste of lumber yards and sustainable forest management practices, making it a fully renewable, carbon-storing option for sustainably minded homeowners. It is naturally moisture-managing and mold-resistant thanks to the addition of borate. Plus, wood fiber insulation is designed for unmatched sound-deadening to create quiet in your most private spaces. It’s also available at multiple thicknesses, such as 3”, perfect for interior wall applications.

For the sake of this guide, we’ll assume your bathroom has been gutted and any walls you plan to insulate are stripped to their studs. Installing wood fiber bathroom insulation is easy. Use a utility knife to cut your batt to the correct size (remember, measure twice, cut once!) and then use your hands to press it between the studs for a snug fit. You can easily cut or tear wood fiber batt to fit around wiring and pipes, ensuring there are no gaps in your bathroom insulation. Check out our DIY guide for more details on prepping and installing batt insulation.

Bonus: Proper Ventilation & The Right Paint

While insulating bathroom walls is a great first step to managing bathroom moisture, preventing mold, maintaining comfortable temperatures, and reducing noise between rooms, your work doesn’t stop there.

Primarily, you need to ensure your bathroom has adequate ventilation to prevent the build-up of moisture. Your bathroom fan should be sized according to size of the room, with the rule of thumb that you need 1 cfm for every square foot of floor area in your bathroom. When possible use durable metal or PVC duct work to vent your fan and try to run ducts as short and straight as possible.

Windows can also offer natural ventilation but without airflow, tend to be less effective—plus someone has to remember to open and close the window. You should also keep an eye on your bathroom windowsill as condensation on the glass can roll down, collecting at the base and causing mold or rot in your window frame. Give these windows a good clean and check your frame every so often.

Your paint choice also has an impact on how your bathroom walls respond to moisture. In high-traffic bathrooms, a semi-gloss finish is easy to wipe and repels moisture, helping you keep your walls clean and dry. Powder rooms or guest bathrooms might be amenable to eggshell or satin finishes that can still be wiped but prefer not to be exposed to frequent moisture.

With every long, steamy shower my partner takes that doesn’t leave behind a trace of mildew, I’m reminded of the important role of our bathroom insulation. Investing in quality bathroom insulation is an opportunity to enhance your quality of life, one foggy mirror at a time.