The Cordwood Sauna

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For sauna, the last of these 5-E advantages is particularly compelling. Cordwood masonry has the perfect energy characteristics for a sauna - excellent insulation combined with exceptional thermal mass. This combination means that heat loss through the sauna walls is minimized, while the short "log ends," as well as the inner mortar joint, act as thermal mass if placed on the correct ( inner) side of the insulation. Once the sauna is seasoned, the fire can go out and the fabric of the building will keep internal temperatures up to the required 150°F to 180°F. I have learned over the years and through various extremes that this is the normal and preferred range of temperatures favored by sauna experts. Adjustments are made for the size of the sauna stove room, as well as the age of the bathers, because large saunas can be hotter than small ones. Children and the elderly generally sauna at a lower temperature than other folks. At our round Earthwood sauna, described herein, we season the stove room for about three hours in the winter and two hours in the summer.

The round shape of the cordwood sauna has two advantages, one practical and one more intuitive. The practical advantage is that the round shape encloses the most space per unit of perimeter. What this fact of geometry means is that when you add the vertical dimension, creating a cylinder, you enclose the maximum volume per square foot of side walls (vertical side walls, at least).

The intuitive advantage is the feeling of warmth and comfort that comes from being inside of a small, round building, Many of our sauna guests describe experiencing an almost womb-like or nestlike sense of security.

Okay, my journey into the history and lore is done, at least for this article. The Earthwood sauna is the best I've experienced, and this is as it should be. The sauna that you build, dear reader, will be the best you've ever experienced too. Now I need to tell you how it's done.

The Foundation

Cordwood masonry, like any wooden wall system, needs to be kept clear of the ground. I like a good solid masonry foundation that extends at least 4 inches shove grade. Although stone could be used for the foundation - if you've got the stones and the time-our Earthwood sauna foundation is concrete, formed with 8"wide strips of 1" Dow Styrofoam® wellposted with 2 x 4 stakes around the perimeter to prevent concrete "blow-out." For the 8"thick cordwood walls recommended for this 10'-diameter building, a footing cross section of 12" wide and 8" deep is adequate. To avoid having to dig footings down blow frost level (4 inches in our area!), scrape the organic material to the edge of the site, and bring in a dump-truck load of good coarse sand. This is used to build a "pad" upon which your circular footings will float. I call this a floating ring beam. If the sand pad drains water from the sauna to a point downgrade, there will be no water to collect under the footings or slab. No water means no freezing; no freezing means no frost heaving ... or the accompanying structural damage. Don't take my word for it: This was also Frank Lloyd Wright's favorite foundation system. It is cheap and easy. And in rural areas the floating slab is becoming the accepted foundation strategy of choice for garages, outbuildings, even homes. Do not pour the floor at this time, just the footings.

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