I’m excited about my latest project: a woodburning mobile sauna.
Unlike all of my other projects, which I design and build to meet the needs of my customers, this one is for myself. Over the past five years, I have been without my own sauna. It’s a long story: basically, I sold my house (and sauna) expecting to buy another and build a new sauna, but because the lending rules changed after the housing crisis, with a bias against self-employed folks, I have been stuck in renter’s hell. So, while my customers have been basking in the warmth of my creations, I have been languishing in a sauna-less purgatory, dependent on the generosity of my clients for the too-infrequent sauna. Like the proverbial cobbler whose kids have no shoes, I have been the sauna builder without my own. For renters like myself, the mobile sauna is the perfect solution.
It is a 5×8 sauna built onto to a commercial utility trailer. It is lined with northern white cedar and fired by one of my custom Lämpimämpi wood stoves. It has an arched roof using laminated bent cedar supports and aluminum sheet. It feels a lot roomier inside than you would think and comfortably holds 4 people. And, yes, it meets the 2,000 pound gross vehicle weight restriction of the trailer so it doesn’t require a huge truck to haul it.
I’ll use this sauna for promotion—look for it at various venues, festivals, including the Ithaca Festival parade (again! with our first appearance of a mobile sauna back in 2014). I’ll be taking this one with me on vacation or to my favorite park or forest stop. So, if you see it, feel free to stop and ask me to show it to you. Who knows, if it is hot I might even have a few spare towels.
The heart of the sauna is the stove, heater, or as the Finns call it, the kiuas. The role of the kiuas is to heat the room. Not like a wood stove, but to heat the sauna rocks, which, in turn, provide the heat and the löyly or steam that make a sauna what it is. In the savusauna, or smoke sauna, which arguably, offers the most authentic experience, there is neither stove nor chimney. There is simply a pile of rocks made into a hearth. A fire is burned within until the rocks are hot (filling the room with smoke) and then, once the fire is extinguished and the room cleared of smoke, the pile of rocks does its thing. Likewise, any sauna, whether it is wood fired or electric, is only ready when the rocks are hot.
When building a sauna, the heater is important. But the rocks are even more important. A good heater will hold a hundred pounds, thus, make good löyly. A cheap heater will provide a few decorative stones and you will feel like you are sitting in an electric oven. I have seen many well-designed saunas in my years and I have seen many poorly built saunas, as well. The worst use some variant of a cheap wood-burning stove with a dented pot of rubble or brick on top. In the best, the rocks are the focal point and they get red-hot. Pick one up and drop it into a pot of water and you can make tea.
Left: Rocks Shipped thousands of miles—only to explode in the sauna! Right: Cayuga Lake beach stones— can you spot the erratics?
The type of rock is critical: they should be igneous in origin, formed deep in the hot earth or in the furnace of a volcano. Think of these rocks as heat loving. Granite, grabbro and basalt are typical examples. The Finnish and Swedish units might use grey peridotite. Then there is shape: smooth and round potato shaped rocks or jagged and broken pieces. I prefer the smoother rocks, but there is argument for using the jagged (more surface area). You can order a box of the latter from Tylö that will come all the way from Sweden. Once I opened a box to find a nice hand written note from the fellow who packed them. Another heater company sent me a box from their supplier in Central America. Apparently they needed a geology lesson. The polished siltstone rocks, once heated, started exploding! If you don’t want to have a box of rocks shipped half way around the world or risk getting impaled by rock shards, you can try to find your own.
Unfortunately, our local stone, meaning the rock that is cemented to the landscape here in Central New York, makes horrible sauna rocks. It is all sedimentary: shale, limestone and sandstone. Born in the bottom of ancient oceans, it does not love fire and will complain by exploding if thrown into one. By the way, baptism by fire is a good way to test your rocks if geology eludes you—a good rock will happily glow red-hot. Thankfully, the glaciers that plowed through here brought with them piles of stone from places north that serve the sauna well. These are glacial erratics. As the glaciers retreated and melted, these stones were left behind. The resulting floods that carved our landscape left piles of these smoothed rocks (mixed in with plenty of local stone) in deltas, drumlins or moraines. I find them in the local gravel pit, which mines an ancient delta, or along the lake at my favorite park (another delta) when the water is low. Sometimes I take milk crates with me when I travel through the Adirondacks and fill them with potato-sized anorthosite rocks—which is what the moon is made of—and other pretty granites.
More important than the geology is the significance of the rocks. A Finn, even if they are using a heater with rocks packed in Sweden, will add a spirit stone or two: stones that come from home or some other special place. Stones all have distinct place markers and are borne of this earth and tied to a particular landscape. Except erratics—these have been swept from their homes in a geologic diaspora and found new homes as immigrants, oddities and beautiful accents against the dull grey of the indigenous rocks. Even though I am made of local stone, coming from generations of Central New Yorkers, I have always related to the erratics: the outsiders, the immigrants, the atypical people. They bring us diversity, new culture and traditions like the sauna. In my next sauna you will certainly find plenty of erractics.
Red Hot Adirondack rocks / My Lämpimämpi stove / Stove wall faced with local field stone including shale.
Finishing a job is always a sweet endeavor. I usually budget in one day of fussiness—a day when I can pay attention to all of the little details, get the stove in place and then, as a last step, give the sauna a test run. This is when I get to see how my efforts have paid off and take note of how the sauna actually fires. Is it hot enough? Is it light and airy and does it have that right sauna “feng shui”? Does it reach a good temperature and would Ozzie, the Finn who started me on my sauna-building path, approve.
The job I just finished is a modest affair: bare bones in that Finnish sort of pragmatism. I converted a kit-built garden shed, the type you’ll find parked on the edge of a big box home store parking lot, into a simple sauna with no dressing room. I liked the challenge of working within a modest budget, and I liked the folks: down-to-earth modern day Helen and Scott Nearing types. I had to remind myself that a sauna does not have to be a luxury item, affordable only by those in the higher income brackets, but that a sauna should be essential and ubiquitous as indoor plumbing.
I lined the inside with knotty pine—a low budget alternative to cedar. Sitting on the top bench I noted that the smell of pine reminds me of my forays into woods here in the east and is a close and familiar smell—unlike the rarefied smell of cedar. Aside from the knots, which will bleed sap forever and inevitably find it’s way into someone’s hair, it is a fine wood to use. It is not as stable as cedar but the inevitable cracks will open the sauna up and let it breathe. We always said that Ozzie’s old sauna at Podunk, with its gappy knotty pine walls and sagging ceiling, felt better than any other.
MyLämpimämpi stove fired fast and hot. The rocks quickly reached good löyly temperature and the first splash of water had me moaning in ecstasy. At no point did I feel that claustrophobic locker-room-sauna feeling of not being able to breathe. The dual windows filled the space with light. The benches will hold the couple, their kids and several neighbors. In term of the essentials, it is a perfect sauna. Nothing more is needed– no fancy tile work, no dressing room, no fancy cedar trim work. It works, plain and simple, and it works well. It was the best sweat I’d had in a while and a good sweat is almost payment enough.
For those of you who want to build your own sauna, I will be teaming up with Maria Maria Klemperer-Johnson, founder of the Hammerstone School for a week long sauna building workshop in September. We will cover theory and practice, focusing on all of the details that go into making a sauna. We will work on a pre-framed structure, finishing out the interior. I’ll teach about the design details like what wood to use, proper ventilation and fire codes and we’ll make everything from doors and windows to benches. The finished 8×12 foot sauna will be for sale when the class is over.
The class runs from September 5-10 and will be held at Maria’s school in Trumansburg, NY. This class is open to any gender and is especially suited for couples who want to make a sauna — and the experience of building their own — a part of their lives.
The one thing that always comes up when people ask me questions about building saunas is: how do you insulate it? Intuitively, one might think that the sauna, with it’s high temperatures, would need more insulation than a house and should be as tight as possible to conserve energy. In fact, I’ve had building inspectors give me a confused list of requirements using such logic. The reality is that a sauna is such a different beast than a living space that most of the calculations have to be thrown out the window. R-value, the number printed on most insulation products, is the resistance to heat flow of a given material for a given thickness for a given temperature difference (delta T) between the hot and cold side of the material. Typically, in our region, delta T is assumed to be 35° but, in a sauna, the delta T might be 165 degrees Fahrenheit! So, in terms of heat loss, we get some very different calculations! To really understand R-value, you need to think in terms of it’s inverse: the U value, or coefficient of heat transmission. U value is expressed in units of Btu/hr/sq. ft./°F, or, plainly, how much heat is lost per square foot for every 1° temperature difference. A typical sauna, with R-13 average insulation, might lose 4000 Btus per hour (or 1200 watts). But, A typical sauna stove generates 25-40,000 btus of heat per hour, so losing 4000 btu’s is not a big deal. (It is more important if you use an electric heater: an 8 kw unit, can only put off about 20,000 btus in an hour.) The other factor to consider is that, unlike a living space, you are not trying to hold the heat for very long. So, you don’t need to stack up piles of insulation in the walls and ceiling. In fact, many old saunas had no insulation at all.
What R factor does not measure though, is radiant heat flow. Radiant heat is like the sun warming your face; it is the short wave radiation that you feel. At higher temperatures, short wave radiation becomes a bigger factor than convection. To contain that radiant heat, we use foil, (think: thermos bottle or emergency blanket) but foil, being highly conductive, only works if there is an air space between it and the heat source. The foil doesn’t have to be visible to work; it can be buried between other layers of materials. In my Saunas, it is behind the cedar, with an air gap.
Saunas are also not meant to be tight, stuffy boxes. They require airflow to move the heated air and steam and to make them comfortable. The old Sauna at Podunk was the best one around because it was old and drafty and it always smelled fresh. Counter to today’s high tech homes, ventilation has to be has designed into the sauna room to let it breath passively; the trick is to do it without creating annoying drafts.
When you sit on the bench and enjoy the relaxing warmth of the sauna, you probably aren’t running all of these calculations through your head- and neither am I! What I do know, from 40 years of sauna experience, is what does and doesn’t work. Mostly, you want a good pile of rocks (kiuaskivet) that are hot enough to alternately bask you in their radiant heat and make good steam (löyly) and convective heat off of the heater (kiuas) to produce waves of heat that gently wash over you as you breathe in the fresh aroma of the sauna. You want air, some light and a feeling of openness and connection to the outdoors. It’s not so much science, as it is art, or perhaps a melding of the two.
If you do have specific questions about designing your own sauna, feel free to give me a call or email. Or better, have me come over for a consult. If you live far away, I can even do one-hour phone or Skype consults. In the future, look for classes I’ll be offering on Sauna building, where I can go over all the science—and art—of Saunas in greater detail.
Recently, I was called upon by a couple who had bought a property with an existing sauna that needed some professional help. The structure was a cordwood affair: a building method where timber framed walls are in-filled with short logs, stacked like firewood, with mortar between them. It looked like it came right out of the pages of Rob Roy’s classic how-to book: The Sauna. The exterior was fairly solid and quaint in a hobbit kind of way, but the interior, in terms of functionality, had some serious flaws. The timber frame and log and mortar walls looked pretty good, but it is obvious that the project was a classic DIY affair: a case of a homeowner taking on a project that looks easy, but with complex details that get skipped due to a lack of knowledge, funds or basic skill.
There are elements to a sauna that are essential: such as a welded steel stove that will not crack or explode when doused with water and the installation of that stove that conforms to the NFPA 311 guidelines. Insulation must be able take the heat, provide proper moisture retention, not attract rodents and not become a health hazard. Doors must open out and have non metal, non-latching hardware and be self closing (ever try to turn a 200° doorknob with sweaty hands?) There must be no varnish or paint in the sauna room; it will only off gas or worse, burn.
This sauna missed all of these points and more. From the pile of starling skeletons in the stove, I can only guess that it has not been used in a very long time (another detail: birds will fly down the chimney only to find themselves in a death trap.) From the lack of tell-tale scorching or smoking of the wood, I could also tell it had not had been used much. In fact, if it had been fired to a decent, Finnish-approved temperature, I am sure it would have either caught on fire or sent it users scrambling to get out as all of the varnished wood off-gassed.
It is a classic example of a DIY affair: started with good intentions but never finished properly. When I went into the house with the owners to discuss my plans for bringing it back to life, they brought out a book that had been left with the house: a dog eared and highlighted copy of Rob Roy’s: The Sauna.
The one thing that always comes up when people ask me questions about building saunas is: how do you insulate it? Intuitively, one might think that the sauna, with it’s high temperatures, would need more insulation than a house and should be as tight as possible to conserve energy. In fact, I’ve had building inspectors give me a confused list of requirements using such logic. The reality is that a sauna is such a different beast than a living space that most of the calculations have to be thrown out the window. R-value, the number printed on most insulation products, is the resistance to heat flow of a given material for a given thickness for a given temperature difference (delta T) between the hot and cold side of the material. Typically, in our region, delta T is assumed to be 35° but, in a sauna, the delta T might be 165 degrees Fahrenheit! So, in terms of heat loss, we get some very different calculations! To really understand R-value, you need to think in terms of it’s inverse: the U value, or coefficient of heat transmission. U value is expressed in units of Btu/hr/sq. ft./°F, or, plainly, how much heat is lost per square foot for every 1° temperature difference. A typical sauna, with R-13 average insulation, might lose 4000 Btus per hour (or 1200 watts). But, A typical sauna stove generates 25-40,000 btus of heat per hour, so losing 4000 btu’s is not a big deal. (It is more important if you use an electric heater: an 8 kw unit, can only put off about 20,000 btus in an hour.) The other factor to consider is that, unlike a living space, you are not trying to hold the heat for very long. So, you don’t need to stack up piles of insulation in the walls and ceiling. In fact, many old saunas had no insulation at all.
Recently, I was called upon by a couple who had bought a property with an existing sauna that needed some professional help. The structure was a cordwood affair: a building method where timber framed walls are in-filled with short logs, stacked like firewood, with mortar between them. It looked like it came right out of the pages of Rob Roy’s classic how-to book: The Sauna. The exterior was fairly solid and quaint in a hobbit kind of way, but the interior, in terms of functionality, had some serious flaws. The timber frame and log and mortar walls looked pretty good, but it is obvious that the project was a classic DIY affair: a case of a homeowner taking on a project that looks easy, but with complex details that get skipped due to a lack of knowledge, funds or basic skill.
