Introduction: Building an Outdoor Sauna

About: Retired software engineer. Like the outdoors, canoeing, camping, hunting and fishing. I’ve built 3 cedar strip canoes and 2 cedar strip kayaks and use all of them. I built 3 acoustic guitars and play all of th…

Since I became a homeowner several years ago, I always wanted to build a Sauna. I blame it on being raised in Michigan's Upper Peninsula where there are many people of Finnish decent. A sauna is a small hot room(140 F to 200 F) where you go to sweat. It promotes relaxation and supposedly good health. I’ve seen a few inside homes and a few outside homes, also some in spas and health clubs. A popular but somewhat peculiar activity is to heat yourself in the sauna then either roll in snow or jump into cool water.

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Shown in the first two photos are examples of traditional outdoor Sauna you might find in Finland or other countries in northern Europe. The third photo is my building.

Step 1: The Beginnings

I have on my property an old concrete block out building which was used to store nothing but junk really. It is not too far from the house. Voila the perfect location for a sauna. I also had an old iron fire place insert sitting around just slowly rusting. Voila a perfect sauna heater.

Step 2: Cleaning the Building

The first step was to clean the outbuilding and throw away any unusable junk that had accumulated for the past several years. There were vines growing into the building from an uncovered eve and mud-dauber wasp nests through out. One half of the ceiling was covered with paneling, which when removed, sent a shower of dirt and assorted debris down onto me.

Step 3: The Plans

Over the years I refined the plans and made several hand drawings and even CAD drawing as I mulled over the perfect Sauna project. When I decided to use the outbuilding I sketched some plans and began to solidify my design. As usual, once I discussed the plans with my wife they changed. She is not a CAD wizard, so she sketched her version in chalk on the driveway. I began work on the sauna interior according to my wifes chalk sketch. We were going to divide the interior space into 3 rooms, the sauna, a changing room and a entry/storage area.

Step 4: Building the Hearth

I next constructed a hearth to house the iron fireplace insert. After much contemplation, I located its position in the sauna room space and decided to run the chimney straight up through the roof. To construct the hearth, I used concrete blocks, which I’ve always called cinder blocks, perhaps incorrectly, as the base. The hearth walls and top were constructed of concrete bricks. It took more blocks, bricks and mortar than I imagined. I used angle iron pieces I cut from an old bed frame along with pieces of scrap sheet metal to span the walls and hold the bricks in place for the top. All was held together with masonry cement. A sauna stove usually heats rocks onto which water can be dripped to add steam. As the top is enclosed with brick and the stove is a steel enclosure itself I don't anticipate much heat transfer to the rocks

Step 5: Setting the Stove

Before installing the heavy 300+ lb. insert, it was repainted with flat black high temperature wood stove paint from Home Depot. Then it was positioned in front of the hearth before the top bricks were placed, and hoisted using a come-along and a nylon tow strap draped over a post in the rafters. I slid right into place with only ¼” clearance on either side. A bit of advice here, measure carefully, several times before building the hearth.

Step 6: Ordering the Chimney Parts

Once I decided to run the chimney straight up through the roof and not through the side wall, I needed to find chimney components. I was looking for a metal double wall chimney system to be fire safe and minimize the clearances I needed. I figured I could use single wall stove pipe up to the ceiling of the sauna then double wall the rest of the way. I began an online search and settled on a company called They seemed to have a very large selection of components. I used their chimney design wizard to specify the components I needed but when the price tag approached $800, I thought I could order “a la cart” and save some money. When the parts arrived and I tried to test fit them together I found that nothing worked. I called the company and timidly explained that I didn’t know what I was doing and needed help. The technical sales person explained that nothing I had ordered would fit together. They were very cooperative with the return and helped me order the correct chimney components. I ended up at about $100 more than my first order but still way less than $800.

Step 7: Installing the Chimney

I hung a plumb bob from the ceiling over the outlet of the stove and marked the inside of the roof to cut the clearance hole. I “dry fit” everything together from the stove to the chimney cap then secured it with extra bracing between the rafters. This building has a sheet metal roof. I thought I could flatten the ridges of the sheet metal with a big hammer then place the chimney flashing over the top. That did not work. Instead I cut the flashing to fit between the ridges along its sides then formed it over the roofing ridges along the top and bottom. Then I applied a very generous amount of silicone roofing cement.

Just to be sure the stove and chimney were really doing the job and to check for smoke leaks I started a test fire with a large wad of newspaper. Smoke came from the top of the chimney and nowhere else. It is recommended that the chimney terminate at least 2 foot above any obstacles, including the roof peak. I know that if the chimney is not high enough it will not draw well.

Step 8: Interior Framing

I started framing before I installed the chimney and completed once the chimney was installed. Since I knew that the paneling would not be pieced together and would span the entire length of each wall, I was not to strict with stud spacing. They were placed approximately on 24” centers. Between each stud I placed 2 in thick Styrofoam panels (approx R-10 value) and sealed the gaps with Great Stuff expanding foam. I found that using a reciprocating saw with a fine tooth blade works well for cutting the panels. I wonder a little about the R value being sufficient. The building is 9 in thick cement block walls, I left about 1 inch air gap between the insulation and the block, and the paneling is 3/4 inch thick cedar. All of this adds some extra insulating factor. The stove is over sized, almost Binford sized, so I don’t anticipate a lack of heat.

Step 9: Re-Wiring

I had to move the breaker box from what is now the entry into what is now the storage area. There are two large wooden posts (approx. 8in X 8in) that sort of support the span of the roof trusses. I think they don’t really help that much to support the structure since they were just wedged in place and held with a few nails through a truss. I moved one of them a clear path to the storage area. The breaker box is mounted on it. I added a recessed LED ceiling light in the sauna room, a cheap ceiling fixture in the changing room, even cheaper ceiling fixture in the entry.

Step 10: Insulating

The next step was to insulate the ceiling with paper backed fiberglass with an R-19 value. Two rolls 39 ft. were enough to insulate the ceiling of the sauna room and the changing room. I am leaving the entry and storage area ceiling un-insulated. On the ceiling and walls I placed a vapor barrier. It was simply one roll of 4mil plastic sheeting. I cut it into wall sized sections to make it more manageable during stapling.

Step 11: Wood for the Interior

Sauna interiors are traditionally made from cedar, but sometimes fir or pine is used. Cedar is more expensive than pine so I used some of each. The ceiling and front wall behind the stove is made from 8” wide tongue and groove pine panels from Menards. This paneling is called “car siding” , a term the snotty and unfriendly gal at the Home Depot service desk was apparently unfamiliar with. They do have the panels, but they are called tongue and groove pine. Apparently my description of cars siding as "pine tongue and groove panels" was not enough for her. The walls are covered with 6” wide Western Red Cedar house siding, again from Menards. I had to dig for a while through the stock of boards to find ones that were suitable. All the paneling is attached with galvanized finishing nails except in the hard to hammer places where I used finishing dry wall screws.

Step 12: Vents

The sauna room needs to be vented, especially if a wood heater is used. The fire would eventually burn off most of the oxygen in the sealed room and starve itself. Not to mention the effects it could have on the bathers. I cut a about a 6 in X 12 in slot in front wall near the floor at a corner and another slot in the ceiling diagonal from the floor vent. Each slot was covered with a piece of scrap wood having holes cut through with a 1/2 in. forstner bit. the holes were counter sunk and the boards attached with screws.

The ceiling vents into the attic and I figured that the clearance hole in the roof for the stove pipe would vent sufficiently to the outside.

Step 13: Benches

When constructing the benches I wanted lower and upper platforms. I decided to make an L shape along the back wall furthest from the stove. There is really only room for one upper and lower platform along the back wall and a lower platform along the side wall. The lower bench is 18” from the floor and the upper bench should have 42” of clearance to the ceiling.

I first constructed frames for the benches from pine 2X4s. The part of the frame against the walls was attached through the paneling to the studs with special 4-1/2 flat headed lag screws. The lower benches had post legs for support and angle bracing also attached to the studs. The upper bench just used angle bracing to allow room underneath. The benches are made from 5/4 Cedar deck planking and roughly spaced 1/2” apart. I cut and placed all the planks first without attaching then adjust the spacing to fill the frames and marked their locations. The front part of each frame where your legs would hang over by the way, is also cedar deck planking.

Step 14: Floor

The floor in my outbuilding is concrete. I decided to just build a wooden platform floor in the sauna room under and in front of the bench area and leave exposed concrete around the wood stove. The platform does not extend all the way to the wall under the widest bench. This saves me some dollars in material cost and leaves an area around the wood stove that will not scorch if hot embers fall to the floor. I laid out 2X4 stringers on the concrete with the 4in side flat on the floor, about 2 feet apart. I then filled the space between with 1” foil backed rigid foam, foil side up. Here again I used 5/4” cedar deck planking and laid the planks before I attached them.

Step 15: Door

Almost done now with the sauna room, I had to make an insulated door. I built a 2X4 frame to fit the door opening with ½” clearance all around. Before constructing the complete door I test fit the frame in the opening, then increased the clearance because of the slight un-squareness of the opening. I added a nailer inside the frame for paneling attachment which had a width calculated to allow 2” of rigid Styrofoam insulation, car siding panels, and scrap cedar plywood to nest inside the frame. The panels were attached with galvanized nails.

I created a contraption of a door handle/latch constructed for salvaged 1X6 oak fence boards. The exterior handle attached to a 1 inch dowel and to an interior latching/handle piece placed perpendicular to the outside handle.

Step 16: Enjoy

The sauna will heat up in about one hour, that is from about 0 degrees F to about 160 F, which is about right for most people. I've had it up to 175 but much more will start to become uncomfortable. We have used it about a dozen or so times in the past 3 months since it was completed It will hold about six or seven people but is most comfortable with 3 or 4. Rolling in the snow after a 15 minute soak is a favorite routine.

Snow Contest

First Prize in the
Snow Contest

Makerlympics Contest

Grand Prize in the
Makerlympics Contest