When the client for my latest mobile sauna project contacted me, he told me he needed something that would look and feel like a sauna from back home in Finland. He wanted it to be wood-fired and to get really hot. He wanted the clean lines and rustic charm of Finnish design and even requested a traditional pine tar finish like what the Vikings used on their boats. As small as it going to be, it was to have the standard two rooms: the sauna room and a dressing room. He also wanted to use the latest solar technology to light it with a soft glow.
But working for an American company where he might get moved from time to time, he wanted it to be untethered to his house and portable, so he could always bring it with him like a cherished possession.
I enjoy challenges. In fact, I thrive on them. One of the advantages of having my own company is that I get to decide how much to put into each project and which projects to really focus on. On some projects, like this one, I get to expand my repertoire. The goal, as always, was to bring my client’s dreams into reality. The result did just that: a mobile sauna on a 81″x120″ trailer, under three-thousand pounds, with a dressing room, solar-powered lighting, custom wood stove, northern white cedar interior, and pine tar exterior finish. I created a little oasis—a reminder of Finland—that my client can park in his back yard. A dream come true.
Saunas are like that. When you have your own, it is a dream come true, a special place to escape into, to relax and unwind. Though tied to old traditions, for many, sauna is a new experience and can be life-changing. As designer and builder, I get to be the midwife for people’s dreams and help them usher in a new way of living or rekindle a past love. As we turn the page to a new year and think about resolutions, what dreams do you want to come true?
Mobile sauna by Rob Licht Custom Saunas.Solar powered lights on mobile sauna by Rob Licht Custom Saunas.
I get a lot of questions regarding sauna insulating details and thought I’d shed some light on a few issues. A caveat before I start: heat transfer science gets pretty complicated, and I am grossly simplifying things here. I’m not an engineer. I rely on experience and am constantly probing and measuring my own saunas to see what works.
A building inspector may want an engineer’s input, but just make sure the engineer understands what happens in a sauna.
If you are building an electric sauna, either in your house or as a stand-alone building, you’ll naturally want to insulate it for efficiency. Normally, builders (and building inspectors) think of R-value (printed on every insulation product label) as the golden metric, and the R-values of a wall assembly are typically added up to get a number that either complies with code or satisfies a self imposed trade-off between cost, efficiency, and practicality. R-value is the resistance to heat transfer. But it measures conduction and convection, not radiation, which is not much of a factor at lower temperature differentials. R-values are calculated with normal living spaces and long-term heat retention in mind, which in a typical home is calculated using an average temperature differential of 24°C (between heated and outside space). Since R= Delta T/QA, (where QA is the ability of the material to transfer heat), and in a hot sauna Delta T might be 100°C, the use of labeled R factors is totally skewed!
The second factor is time. Heat loss is measured in BTUs/hr. With the sauna only on for a few hours a week (bravo if it’s more!), your heat loss will be minimal, and hopefully, in the cold months it will contribute to heating the house. So, in terms of cost vs. efficiency, a lot of insulation may be overkill.
At the higher temps of the sauna, the radiant effect of heat is more of a factor, and the use of a radiant foil barrier comes into play. The heat you feel radiating from a wood stove is the long wave radiation. This radiation can move through common building materials, but foil stops it dead in it’s tracks. Anyone who has nestled under an emergency blanket or protected themself from the fiery radiation of a blast furnace (like when I pour bronze), understands the effectiveness of foil to bounce radiation back towards the heat source. But if the heat source contacts the foil layer, the aluminum superbly conducts the heat, defeating the purpose. So, when building a sauna, it is the radiant foil layer with an air gap on the hot side that is crucial to holding the heat in. This should be backed by as much standard insulation as is practical, but don’t worry about attaining super R-value. The exception being if the wall is an outside wall of the house and a part of the building envelope. In this case, R-value must be a minimum of what the rest of the house has. I prefer mineral wool, but in any case, do not use XPS or EPS foam directly behind the foil, as they will melt at sauna temps!
Vapor control in an interior sauna is really important especially, in modern tight houses. These structures tend to trap moisture. Vapor can cause damage that you can see, such as peeling paint, but also damage you won’t see, like moisture condensing in a wall cavity. A radiant-foil barrier, when carefully taped at the seams, is also a perfect vapor barrier. When I build interior saunas, I think about all of that moisture and imagine where it can get to and wreak havoc. I then seal off those spaces, and provide a vented path for moisture to escape.
Some enthusiastic löyly action will turn ladles of water into steam, which fills the sauna and then escapes into the house—like when you forget a kettle on the stove and all your windows fog up.
The best thing is to build your sauna next to a shower area and then vent that adjacent area with a decent bath fan to the outside or via the household HRV system. The sauna should also have an air intake under the heater, as per manufacturer’s instructions, and via a gap under the door so the sauna gets a healthy exchange of fresh air. Never connect the sauna directly to a mechanical ventilation system.
With careful planning of layout, insulation, ventilation, moisture control, and a heater that makes good löyly, your indoor electric sauna can feel like a wood burner on a pond’s edge and also be an integral part of your efficient home.
Sauna is all about perfection. Not over-the-top polished perfection, but a perfect way of being: simple, pure, functional. Perfect living. Harmonious. After all, you enter the sauna naked, our perfectly imperfect bodies exposed but hidden in the dim light. You sweat out the toxins of life and leave with a clean aura. Like the Japanese concept of wabi-sabi, the sauna encourages acceptance of the imperfect as natural and beautiful.
When I work on my saunas, I am constantly aware of this balance. Too much perfection will ruin the relaxed atmosphere; too many crisp details will hold tension in the materials. I relax when I work, become one with my materials and try to imbue the building with a human inexactness.
All details are all made by hand or by nature: the pulls on the doors (hickory branches); the handle on the stove (made by me, wrapping stainless rod—like wrestling a snake); the benches (massaged with sand paper) and the funny round window (imperfectly round, like the eye of a whale). The stone facing on the wall around the stove was pulled from a hundred-and-fifty-year old barn foundation and carefully split with whacks from the hammer my great grandfather used to carve head-stones. The dressing room floor is reclaimed fir, every bit as tough as the day the trees were felled. I use some new materials, but they never look like I just pulled them off the shelf in some big-box store.
I’ve touched all the pieces of the sauna many times—each board, each stone, each piece of metal. I carry slivers of each project in my hands for weeks—a constant reminder of the work I do. I think of our physical world built by hands: every brick in every building handled, touched and in the memory of some callus, everything we think of as solid and real created by someone’s toil. Even the rocks that mark the hedgerow at the back of the sauna were placed by hand almost two centuries ago. The sweat of that farmer’s labor infusing with the thick clay soil.
My last project was nearly perfect—which is as close to perfect as I want it to be. Great client, perfect site, easy access, and nice new pond with a beautiful dock and deck. Ok, I did order the wrong color roof but the multiple drives back and forth to Mid Lakes Metal, up and down the spine of the ridge between the lakes, were perfect. With my windows wide open, I could taste the salt of the earth and was reminded of why I call this place home.
THANK YOU for you enjoying my blog about saunas and sauna building. If you value the info you glean from my sauna blog consider dropping me a TIP via PayPal @RobLichtStudioLLC or writing a google review. For press Inquiries please contact me directly.
