A sauna is a great addition to a cabin or a house. It is best to have water nearby to cool off.
Step 1: The Base
Check with local authorities about building permits and regulations. There may be regulations regarding drainage. For this built, I dug a hole and put a blue plastic barrel in the hole. The barrel was filled with holes. I back filled around the barrel with small rocks and put a drain in the middle of the shower room and the sauna room leading to the barrel. I also put a drain in the shower base leading to the barrel. This way. all water used in the sauna drained into the barrel and then leaked out into the ground.
This sauna base is 8 x 13 feet. It will have a shower room and a sauna room that comfortably seats six people.
Don't forget to use end cut paint on any pressure treated lumber that you cut. Lay two rows of three deck blocks for each support beam and level them. Put two 13 foot pressure treated support beams on the deck blocks.
Put pressure treated 2 x 6 for each side and ends and nail in joists at 16 inch centers. Attach the joists to the support beams with hurricane ties. Cover the bottom of the joists with mouse screening and use rockwell insulation for the floor. Screw down the 3/4 inch thick subfloor. It's a good idea to put a 3/8 inch shim under the subfloor around the outside of the sauna room and the shower room. This way the water will run towards the drain when it is finished.
Step 2: Framing
Frame the outside walls and an interior wall that is half way between the two ends. Frame a door in the interior wall. Also, frame a rough 13 inch by 13 inch space in the interior wall for a window. Have a 12 inch by 12 inch single pane of glass cut to put in this space later. Frame an exterior door and window in the shower room. Frame two vents on the outside walls of the sauna room, one at floor level and one on a different wall at three feet high. Frame an opening for the wood stove. I would highly recommend an exterior loading wood stove. It prevents the mess of the wood stove inside the sauna room and gives you more room inside.
Install the exterior door and window. Cover the outside walls with sheeting and then vinyl siding or the exterior of your choice.
Step 3: The Roof
Make your trusses, making sure that you have a truss gap where the chimney for the wood stove is going to go. In this build I used metal roofing. For metal roofing, you need to put 1 x 3 strapping at 16 inch centers perpendicular to the trusses and then screw on the metal roofing.
If you are using asphalt shingles, you will need sheeting, ice and water along the edges and then the asphalt shingles.
Frame in the chimney support and put up the chimney. Put the gasket over the chimney on the roof and caulk all the edges.
Put on the soffit and facia.
Step 4: Inside Walls
Because the sauna is subject to high heat and humidity, the inside needs some special materials. Use rockwell insulation on the walls and ceiling and then tinfoil vapour barrier in place of regular vapour barrier. The interior wall needs insulation and then tinfoil vapour barrier ONLY on the sauna room side of the wall. If you put vapour barrier on both sides of the wall, moisture can get trapped inside the wall and rot the wood.
Buy a cedar door or make one by gluing and nailing (galvanized nails) 1/4 inch thick cedar over a regular door. The handle of the door needs to be cedar also. Metal handles get too hot and plastic handles can melt.
Put vinyl flooring on the floor, running it up the walls about four inches on each side. The vinyl flooring doesn't have to be pretty as it will be covered with cedar duckboard later. Put a shower base where you want your shower and attach the drain to the piping going to the blue barrel. Attach drain covers to the drains in the center of the sauna and shower room.
Where the wood stove is going, install cement board or other nonflammable board. Paint it with heat resistant paint. Alternately, you can purchase stove shields and screw them onto the wall, leaving a one inch gap. Check the stove and stove shield for allowances.
Step 5: Cedar Tongue and Groove
Put tongue and groove cedar on the walls and ceiling. Use galvanized nails. Do the ceiling first then start at the floor level, covering the vinyl flooring that you ran up the walls. Finally, use 1/4 inch thick cedar for trim around the door and window frames. Stick regular heating duct vents over the two vents in the sauna room.
Put 1/2 thick x 2 inch wide cedar stock around the inside window. Place the single pane glass against it and then put 1/2 stock wide enough to be flush to the other side. Put 1/4 inch trim around this interior window on each side.
Step 6: The Shower Room
Put an electric light or hook for a lantern outside the window in the shower room so it will shine into the sauna. You may also want to make a pail shower if you don't have running water coming into your sauna. Here is how you make a pail shower. Buy a rectangular pail, a faucet with a threaded pipe, two thin nuts that fit on the pipe and some silicon. Cut a hole in the side wall of the pail near the bottom. You can't put it right at the bottom because you need some clearance for the inside nut. Put the first nut on the pipe thread as far as it will go. Put silicon on the inside and outside of the hole and push the pipe so that the nut is snug against the pail. Put the second nut on from the inside and tighten it until the faucet is firm. Make a shelf for it.
Make a cedar bench along one wall in the shower room and install some wooden pegs along the walls for hanging up clothes.
Step 7: The Wood Stove and Sauna Room
Push in the wood stove so that it is even with the outside of the sauna. Install the stove pipe and decorative cover.
Build the sauna benches. This size sauna can fit three benches, one 20 inches wide and the other two 16 inches wide. They should each be about 16 inches high. Nail (galvanized nails) supports onto the sides and back. Place upright supports in the middle for each bench. Screw the top boards from the bottom. If you have screws exposed where you are sitting, they can become very hot and burn you so no screws or nails should be exposed.
Step 8: Trim and Overhang
Make an overhand above the exterior opening of the stove. In the winter, snow will melt when the wood stove is going and drip on you as you load the wood stove otherwise.
Slide metal roofing under the existing roofing and secure. Mount two posts on deck blocks and cut them to the height of the far end of the overhang. Put a 2 x 4 between the two posts at the top to support the roof at the far end.
Put duck board on the floors. Cut 1 x 3 cedar and lay it on the floor at 12 inch centers. Lay 1 x 3 cedar perpendicular to these supports. Screw them in from the bottom. If you have screws from the top, they will become very hot in the sauna room and burn you when you walk on them. It is a good idea to make the duck boards in sections so that they can be easily removed when you want to clean the floor.
Once you are done, light the fire and enjoy the experience.