How to Build a Sauna In Your Backyard

Building a sauna in your backyard sounds like a dream, doesn’t it? A perfect, cozy escape from the hustle and bustle of daily life. Somewhere you can unwind, relax, and enjoy the healing benefits of heat therapy. At least, that’s what I thought when I decided to take on the project of building my own sauna.

I envisioned a quick weekend project, an afternoon of hammering away, and before I knew it, I’d have a beautiful little oasis of warmth and wellness in my backyard.

Spoiler alert: I was wrong.

Turns out that building a sauna isn’t as simple as throwing some wood together and plugging in a heater. It’s a process that requires planning, patience, and a whole lot of learning along the way. I’m so glad I stuck with it, despite the challenges and setbacks. The final result is more than worth it, plus I got some great times with friends, and you get to read this overly-detailed blog post! 

In this post, I walk you through my sauna-building journey, sharing the lessons I learned the hard way. From understanding the unique Finnish style of sauna building to choosing the perfect heat source (and yes, a LOT about ventilation). So, grab a cup of tea, get comfortable, and let’s dive into how I built my own outdoor sauna—and what I learned in the process.

Why Sauna?

Before we jump into the step-by-step of building a sauna, let me tell you why I decided to take on this project in the first place.

 If you’re anything like me, you’ve probably read about the numerous health benefits of sauna use. Everything from improving circulation and relieving muscle tension to boosting your immune system and detoxifying your body. I’ve said many times that if the sauna were a pill, we’d all take it. But since it isn’t, I decided to build one!

A 2015 Finnish study looked at the benefits of sauna 4-7 times a week, and for this to be even remotely practical, a home sauna is really helpful. Of course, there are sauna kits and pre-made saunas, and I link to all the ones I’ve tried and liked below. It’s actually an embarrassingly large amount. But I like doing things the tough way, so DIY it was. 

Lesson 1: Planning Is Key (And Even Then, It’s Still Hard)

The first lesson I learned was that planning is crucial when it comes to building a sauna. Even with the best intentions, things don’t always go as smoothly as you hope. I thought I had everything mapped out perfectly. I measured the space in my backyard, researched materials, and even watched a few YouTube videos on do it yourself sauna building. A DIY sauna project would be a weekend project—nothing too crazy, right?

But here’s the thing: it’s easy to overlook all the small details when you’re caught up in the excitement. The complexity of the sauna construction started to become clear pretty quickly. There are so many factors to consider when you build it yourself, from the foundation to the insulation to the sauna door. One of the biggest challenges I encountered was getting the sauna to be properly insulated. Saunas are all about retaining heat. Without the right insulation, all the effort you put into building the structure won’t result in the cozy warmth you’re after.

I also learned that building a sauna is a bit like solving a puzzle—it requires a lot of trial and error. Especially when you’re working with different building materials and figuring out how to fit everything together. The process wasn’t fast, and it definitely wasn’t easy, but the satisfaction of completing something by hand made it all worth it in the end. (Unrelated: I also learned that I’m not the best at spacial drawing and mapping out dimensions. Thankfully, that ended up all being fixable, though the sauna grew a couple of feet in the process… whoops!). 

The building materials I used after much research:

• Untreated pine lumber as the frame
• Smartside siding on the outside for durability
• Mineral wool as a non-toxic insulation inside the walls (instead of fiberglass)
• Aluminum vapor barrier on the inside once insulation was installed
• Exhaust fan for mechanical downdraft
• Alder wood and some cedar for the interior and sauna benches
• Two 4-light infrared panes from Creatrix for red light and near infrared: https://www.creatrixaffiliates.com/208.html (yes, this technically breaks the rules of a pure traditional Finnish sauna, but my skin loves it, so it’s staying) 
• Huum heater (more on that later)

These same materials can be used to refinish/repurpose an existing outbuilding. Just be sure all treated wood and anything that can offgas is sealed within the vapor barrier. Or, as I did, these materials can be used to build a sauna from scratch. 

Lesson 2: The Finnish Style of Sauna Building

One of the most important things I discovered during this project was the Finns style of sauna building. Finland is the birthplace of the sauna, and their traditional saunas are the gold standard for sauna enthusiasts worldwide. To truly appreciate the art of sauna building, I knew I had to understand the principles behind it.

In a Finnish-style sauna, there are two main elements that make it truly unique: heat and ventilation.

Heat: The Secret to Sauna Therapy

The heat in a sauna is what gives you that satisfying, relaxing experience. It’s also what makes the sauna such a powerful tool for promoting health and well-being. When building my sauna, I had to think about how to generate the right kind of heat. This wasn’t just about choosing a heater (we’ll get to that later) but about creating an environment where the heat would be evenly distributed throughout the room.

Traditional Finnish saunas often use wood-burning stoves to generate heat. However, there are other options, like electric heaters, that can work just as well. The key is to ensure the heat is able to circulate effectively, creating a consistent temperature. This is where the proper design and insulation come into play and where I ran into a few hiccups early on.

When it comes to the health studies on sauna benefits, the main mechanism studied and identified is the heat itself. It’s up for debate if infrared sauna provides a “deeper heat” or helps with detox. Yet the data is clear that with the right amount of heat and time, sauna can be very beneficial. 

For this reason, I knew I had to make sure the sauna could get to 170 degrees at a minimum. I then added the infrared/red lights as a bonus. 

Proper Ventilation: The Missing Piece in Many Saunas 

Now, here’s something I didn’t fully appreciate before I started building my sauna: it’s not just the heat that makes a sauna effective, it’s the ventilation. In fact, I quickly learned that heat alone is not enough to prevent fatigue or discomfort during sauna use. It’s actually the CO2 buildup in the room that can cause us to feel tired or lightheaded. Check out my podcast with Mike Feldstein where we delve more into CO2 here. 

To avoid this, it’s essential to have proper ventilation. This is where the downdraft system comes in. There are two main types of downdraft: mechanical downdraft and manual downdraft.

• Mechanical downdraft uses a fan or vent system to circulate the air and remove excess CO2 from the sauna. This is a more modern solution and can be effective in ensuring the air remains fresh and breathable.
• Manual downdraft is the traditional approach, where you rely on strategically placed vents to allow fresh air to flow into the sauna naturally. Many pre-made saunas either don’t have ventilation or rely on this type.

I chose the mechanical downdraft method for my sauna because I knew we’d want to have longer sauna sessions and be able to host bigger groups. By installing a vent above the heater and a fan under the bench, I was able to allow for the correct flow of air and keep the CO2 levels in check. This setup not only made the sauna more comfortable to use but also ensured that the heat remained efficient.

Lesson 3: The Law of Löyly – Why I Chose Taller Walls and an Elevated Bench

One of the key design choices I made when building my sauna was to go for a taller structure with 8-foot walls. This decision was driven by a deep respect for the traditional Finnish sauna experience and a desire to honor the law of löyly—the guiding principle of sauna heat distribution.

In Finland, the sauna is much more than just a room with a heater; it’s a ritual and a science. The Finnish concept of löyly refers to the soft, enveloping heat and the sense of warmth that fills the space when the sauna is properly designed. It’s all about creating a harmonious balance between the temperature and the airflow. This way, the heat circulates evenly throughout the room. The law of löyly emphasizes the importance of heat rising to the upper benches, ensuring that the person sitting there enjoys the best of the sauna’s heat.

In traditional Finnish saunas, the upper bench—where people typically sit to enjoy the sauna—is positioned above the heater, allowing the body to be exposed to the hottest air. To make this happen, the sauna must have enough height to allow the heat to rise naturally and envelop the user. I ensured that the upper bench would be positioned at the perfect height by opting for 8-foot walls. This allowed my feet to sit at or above the level of the sauna rocks, the source of the heat.

It wasn’t just about creating more room; it was about aligning the sauna with the principles of löyly. This positioning allows the heat to rise and circulate around the body, creating an immersive experience of warmth without overheating or discomfort.

The Benefits of Taller Walls and Elevated Benches

1. Even Heat Distribution: The main reason I chose a taller sauna was to give the heat room to rise and spread evenly. With the upper bench positioned higher than the heater and the user’s feet placed at or above the level of the sauna rocks, the warm air naturally fills the upper part of the sauna. The air then creates a more consistent and gentle heat. This setup encourages better heat circulation. Your body also stays warm from head to toe while avoiding the discomfort of hot spots or cool zones.
2. A More Authentic Finnish Experience: In Finland, saunas are an art form, and the experience is all about balance. Taller walls and proper bench positioning ensure you’re sitting in the right place to feel the true essence of löyly. The rising heat should fill the room naturally, creating that signature soothing warmth essential to the Finnish sauna experience. When I sat on the upper bench of my sauna for the first time, I immediately felt the difference. There was a smooth, enveloping warmth that felt like it came from all around, not just from the heater below.
3. Improved Ventilation and Airflow: By allowing the heat to rise and circulate freely throughout the sauna, the design also helps with ventilation. Taller walls create a space where the warmer air rises naturally and the cooler air flows downward, promoting the ideal exchange of air. This is especially important in traditional saunas where manual downdraft ventilation plays a crucial role in ensuring fresh, breathable air.
4. Comfortable and Relaxing: When your feet are positioned at or above the level of the sauna rocks, it also allows for a more relaxed sitting posture. You’re not sitting too low to the ground, which means you’re exposed to more of the warm, rising air. This setup helps create a more comfortable and therapeutic sauna session. Here you can truly relax and feel the full benefits of the heat.

Lesson 4: Choosing the Right Heater

One of the most crucial decisions I made during the building process was choosing the right heater. After all, this is the heart of the sauna experience. The right heater can make all the difference when it comes to heat quality, energy efficiency, and overall experience.

I did a lot of research before settling on a heater, and ultimately, I went with the HUUM Hive heater. Here’s why:

• Energy Efficiency: The HUUM Hive is designed to be highly energy-efficient. This means I can enjoy long sauna sessions without worrying about high energy bills. It also heats up quickly and evenly, providing a comfortable and consistent temperature.
• Design: The sleek, modern design of the HUUM Hive fits perfectly with the aesthetic I wanted for my sauna. It’s minimalist yet stylish and adds to the overall ambiance of the space.
• Performance: The HUUM Hive uses high-quality stones to generate heat. This helps maintain a consistent temperature and create that soft, enveloping warmth I love.
• Size: The HUUM Hive comes in various sizes, which was perfect for my sauna. I was able to choose the right size based on the space I had available and the level of heat I wanted to achieve.

The heater size is very specific to the size of the sauna and the desired temperature. This heater would not be appropriate for smaller saunas and there are more budget-friendly options for heating smaller saunas. I used this heater from Vevor when I had to replace the heater in my barrel sauna.

Here’s how to calculate the size of a sauna heater:

• Measure the volume of your sauna room in cubic feet.
• As a general rule of thumb, allocate 1 kilowatt (kW) of heating power for every 50 cubic feet of space. Essentially, divide the cubic footage by 50 to get the required heater size in kW. Always round up to the nearest available heater size if necessary.
• You can also use a tool like this one to calculate your heater size.

Lesson 4: Learn Some Patience 

I think one of the biggest lessons I learned throughout this process is the importance of downtime and patience. When things don’t go according to plan, it’s easy to get frustrated. However, taking a step back and allowing things to come together slowly can make all the difference. There were plenty of days when I was tempted to rush through the project, but in the end, I’m so glad I didn’t.

The process of building my sauna took longer than I expected, but it gave me the opportunity to make adjustments, improve my design, and learn along the way. Now, I’m able to appreciate the end result even more because I know how much effort went into making it perfect.

The Final Result

After months of work (and some occasional setbacks), my backyard sauna is finally complete. Well, except for the final roof, but that’s a story for another day. It’s a cozy, warm, and inviting space where I can escape from the world and focus on my well-being. Every time I step inside, I’m reminded of the lessons I learned, the mistakes I made, and the joy of building something with my own hands.

If you’re considering building your own sauna, I hope this post has given you some helpful insights and practical tips. Building a sauna isn’t easy, but the end result is absolutely worth it.

Don’t Want to Build?

If my experience deterred you from wanting to build one (wouldn’t blame you for that), I’ve also tried a lot of other types of saunas over the years. These have included various sizes of portable, pre-made, indoor saunas, and build-from-kit saunas. Some of these include wood burning saunas, while others are portable, personal saunas (like a blanket).

These are the ones I’ve tried and would recommend:

Do you use a sauna? Is this something you’d like to try or incorporate more into your health routine? Leave a comment and let me know!