My latest mobile sauna project started when a customer contacted me wanting a mobile sauna she could use for hot yoga. It’s my standard five by eight foot trailer sauna but without the benches. The arched roof allows for plenty of room for stretching out and the floor is soft cedar. The heat comes from a Scandia propane-fired heater. It’s a cute little unit that weighs under 2000 pounds. Tow it to the next yoga retreat and show off your downward facing dog
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 was 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 un-tethered to his house, to be 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: a mobile sauna on a 81 by 120 inch trailer, under 3000 pounds, with two rooms, solar powered lighting, custom wood stove, northern white cedar interior, and pine tar exterior finish, did just that. I created a little oasis— a reminder of Finland—to 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. It is tied to old traditions but for many, it 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?
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 but 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 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 BTU/ hr. With the sauna only on for few hours a week (bravo if it’s more!) your heat loss will be minimal and hopefully, in the cold months, will contribute to heating the house. So, in terms of cost vs. efficiency, a lot of insulation may be over kill.
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 himself from the fiery 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- then, 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, which tend to trap moisture, both for the damage vapor can cause that you can see, such as peeling paint, but more for the damage you won’t see, like moisture condensing in a wall cavity. 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 but provide a vented path for it to escape. Some enthusiastic löyly action will turn ladles of water into steam which fills the sauna but 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 area with a decent bath fan to the outside or via the household HRV system. The sauna should then have an air intake under the heater as per manufacturer’s instructions and via a gap under the door so 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 but also be an integral part of your efficient home. (Read more about Sauna foam and best sauna building materials at Sauna Insulation, Revisited)
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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. 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.
It’s all made by hand or by nature: the pulls on the doors (hickory branches), the handle on the stove (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: reclaimed fir, every bit as tough as the day the trees were felled. I use some new materials but never looking like I just pulled them off the shelf in some big box store.
I’ve touched it all 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 infused with this thick clay soil.
This 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, down the spine of the ridge between the lakes was perfect. With my windows wide open, I could taste the salt of the earth and was reminded of why I call this place home.
All summer long I have eagerly anticipated this week; we have a cottage rental on the lake. It’s the highlight of my summer and a much-needed break from all of the projects I have going on. This year, in addition to the usual activities—swimming, canoeing, beach fires, collecting beach glass and just staring the waves while sipping wine—I’ve added one more: sauna! I’ve brought my wood-fired trailer sauna with me and parked it ten feet from the water’s edge. Nothing beats coming out from the hot steam of a good löyly and jumping into the cool, refreshing lake. It is perfection.
My good friend Daniel has come home for a few days so we decided to take the trailer sauna down to Podunk, his family’s homestead, where, as a youth, I was indoctrinated in the way of the sauna. The old shack built by the original Finnish owner of the property has long since gone to the squirrels, but our memories of saunaing on cool summer evenings are still as vivid as the lush green canopies of the giant poplar trees that stand as sentinels in the field by the riverbank, keeping the creek from advancing any further as it swishes across the valley. On a geologic scale, the creek— the same that carved the falls at Taughannock— slithers like a snake, back and forth, carving a new path every few years. In our short lives we can remember when it made this turn or that, turning a rocky bank into an inviting swim hole or turning the old dipping spot—the one we would run down to from that old sauna, hooting and hollering— into a rocky shallow.
There is a new swim hole now. It’s an Olympic sized pool compared to what we used to dip in, allowing for real swimming as opposed to the slow rolls we used to take in the knee deep water just below where the pipeline crosses. As we lay there with our heads pulsing from the effect we called “sauna stoned,” minnows would nibble on our fresh cooked skin. With this new hole, the creek is more perfect for a sauna now than it was then.
I parked the trailer just on the edge of the bank and fired it up. The fact it was close to the creek where the spring high water often lapped the trunks of the poplars did not matter; this was a temporary affair, a brief encounter with our own youth, a dip into the pool of nostalgia. Once it was hot we climbed aboard and were transported back in time some forty years. My little stove holds a hundred pounds of rocks, all glacial erratics, transported here by the great river of ice in a time before memory. When heated, those rocks are capable of producing the best löyly, letting off a burst of steam that sends us out the door and clambering down the banks to the sweet cool water of the creek. It’s impossible not to let out a few whoops.
It’s good to be back home.
