DIY Sauna Insulation: A Complete Guide With Expert Tips And Tricks

Whether you’re installing a sauna or simply upgrading it, proper insulation is absolutely crucial. In fact, as a sauna expert myself, I’ve seen firsthand how the right sauna insulation can make all the difference in both performance and longevity. 

After all, not only does it help maintain the perfect temperature for your sessions, but it also ensures that your sauna stays energy-efficient.

Nevertheless, when it comes to insulating a sauna, things can get quite tricky. That’s because you’ve to figure out everything from insulation materials to the right procedure, and more. 

But that said, you can still insulate your sauna by yourself. And help you with it, I will walk you through all steps of insulating a sauna, plus tips and techniques I’ve learned over the years. 

Read on and know you can go about insulating your sauna. 

Why do you need to insulate a sauna?

I am often asked why insulating a sauna is so important. So, before I start with the sauna room insulation process, let me address this once and for all. 

For starters, insulation minimizes heat loss and helps reach the desired temperature much more easily. And this, in turn, keeps your sauna sessions energy-efficient. 

Not to mention, the right insulation also retains heat and maintains optimum temperature throughout your session. 

What’s more?

Insulation materials provide a crucial barrier against moisture and aid overall sauna venting. This prevents condensation and provides protection against structural damage, mold, and mildew. 

The result: Your sauna keeps in tip-top shape for years. 

Sounds awesome, doesn’t it? 

Sauna insulation: Here’s how you can do it yourself

Now that you know why it is so important to insulate sauna properly, you might well want to start insulating your sauna right away. 

And to make DIY insulation simple for you, I’ve divided the whole process in two, namely material procurement and insulation steps. 

Here, you’ll first purchase all the materials that you’re going to need. Thereafter, you can follow the steps I’ve detailed to insulate your sauna enclosure like an expert. 

So, let’s get started!

Get the right sauna insulation materials First thing first, you’ll need to source the right materials for insulating a sauna. That’s because materials can make or break the quality of insulation in your sauna. 

And to that end, here are a few materials you can choose from: 

Option 1. Mineral wool or rockwool
Mineral wool is known for its excellent heat resistance and moisture protection and it’s ideal for insulating sauna walls and ceilings. 

In fact, there are many upsides to working with mineral wool since it's durable, easy to work with, and provides a strong barrier against heat loss. 

Option 2. Foam boards
Foam boards, such as polyisocyanurate, offer high R-values, or in simple words they provide superior insulation. 

These boards offer easy installation and their insulating properties are simple to maintain. And this makes them a great option for both walls and ceilings.

Option 3. Recycled cotton
If you’re looking for a more sustainable alternative, you can go for recycled cotton. This material has an R-value similar to fiberglass but without the risk of handling issues. 

And although it is more expensive to source, it’s safer for your health and the environment.

Bonus: Also source material for vapor barrier 

A vapor barrier installation is essential to insulating your sauna without leaving any gaps for moisture intrusion. And to do so, I suggest you get aluminum foil as it reflects heat back into the sauna and prevents moisture from reaching insulants.

Follow the right steps to sauna insulation

Having soured the insulation materials, it’s now time you start insulating your sauna bath. And let me tell you it isn’t as complicated as it seems, all you’ve got to do is follow my step-by-step DIY process. 

All in all, here’s what you’ll do: 

Step 1. Prepare the sauna frame
Before you start with insulation, I suggest you first check if the sauna frame is solid and correctly constructed. 

You see, the frame is the backbone of your sauna. And if it’s not built properly, your insulation won’t work as effectively. 

So, you can begin with checking for any gaps or areas that could let heat escape and make sure the frame is well-built.   

Step 2. Install the insulation materials
This is where you install the insulating materials. Now, here are a few excellent options, but my go-to choices are mineral wool and foam boards. 

Why? 

Well, mineral wool is fire-resistant, offers great heat retention, and prevents any moisture buildup whatsoever. 

At the same time, foam boards are easy to work with and provide a solid thermal barrier. 
But, notwithstanding the material you choose, your goal should be to create a tight fit with no air pockets. 

Step 3. Install the vapor barrier
Once the insulation is in place, the next step is to add a vapor barrier And for this step, I always suggest using aluminum foil since it is highly effective in reflecting heat and blocking moisture.

Pro tip: Make sure you overlap the seams properly when installing it to create a completely airtight seal. 

Step 4. Ventilate the space
Often overlooked, ventilation is one of the most important elements of a sauna insulation; more so if you’re building a sauna in the basement. That’s because with a lack of optimum airflow, you risk moisture buildup. 

You can install a ventilation strip at the top of the sauna, as it will release moist air while maintaining the integrity of the sauna roof. And this will, in turn, ensure that your sauna remains dry. 

Step 5. Weatherproof (for outdoor saunas)
If your sauna is built in an outdoor space, it would have its own set of challenges given higher exposure to the elements. 

So, the first thing you’ll want to do is weatherproof the exterior. Here, you’ll install siding materials and flashing properly to prevent water from seeping in. 

And to do so, I suggest you use breathable membranes like Tyvek. This will protect the structure while allowing any trapped moisture to escape. 

Frequently asked questions about insulating a sauna

Does a sauna need to be insulated?
Yes, a sauna absolutely needs to be insulated! 

Insulation plays a critical role in ensuring that your sauna retains heat efficiently. And a lack of proper insulation will let heat escape and your sauna will have to work much harder to maintain the desired temperature. 

This not only wastes energy but can also lead to longer heating times, making your sauna less effective.

Can you use spray foam insulation in your sauna?
Spray foam insulation might seem tempting due to its excellent air-sealing properties. But there are some things to consider before you use it in your sauna. 

You see, the main concern with spray foam is off-gassing at high temperatures, which can release harmful chemicals into the air. This is why I suggest you be cautious and only use spray foam materials that are rated for high temperatures. 

How thick should your sauna insulation be?
The thickness of insulation will depend on your climate and the insulation material you’re using.

Generally, walls require insulation between R-13 and R-19. Ceilings, at the same time, need insulation between R-22 and R-30. 

Nevertheless, it’s always a good idea to consult your local building experts and consider the temperature extremes in your area. And if you’re in a particularly cold climate, thicker insulation will help keep your sauna energy-efficient and comfortable year-round.

Is a vapor barrier necessary for both indoor and outdoor saunas?
​Absolutely! Whether your sauna is indoors or outdoors, a vapor barrier is critical. This layer stops moisture from seeping into your insulation, and, in turn, prevents mold, mildew, or structural damage.

Also, the vapor barrier helps keep the insulation dry and ensures that the heat stays inside.

Can you insulate an existing sauna?
Yes, it is possible to insulate an existing sauna. But, it can be a bit tricky. 

Here, you’ll be retrofitting insulation which will involve disassembling the interior panels to access the walls and ceiling. And in some cases, you’ll also need to work with a professional who can assess the condition of the existing insulation and make sure that new insulation is installed properly. 

What is the best insulation for a mobile sauna?
Mobile saunas need lightweight and durable insulation. So, I suggest you use a combination of closed-cell spray foam for structural support and mineral wool for heat resistance. 

To sum up

As you can see, sauna insulation is not as difficult as it seems. And I am confident that you can DIY your sauna room’s insulation perfectly with all the materials and steps I’ve detailed above. 

Got more questions or need expert sauna installation in your home? 

You can get in touch with us!

At Steam & Sauna Experts, we are seasoned sauna and steam room installation experts with over a decade of expertise installing top-notch home sauna. Also, we’ve got the best sauna equipment from industry-leading manufactures at pocket-friendly prices. 
In short, we’ve got all your sauna bathing needs covered

​