Difficulty:Moderately ChallengingTape measureStakesTwineShovelLevelRedwood tongue-and-groove planking2-inch by 4-inch redwood lumberPencilSawNailsBoltsPlywoodRoll insulationScrewsCement particle boardFlashingSauna stoveJigsawSandpaperHingesLatch1
Mark out an area 6 feet long by 5 feet wide, using stakes and twine. Dig down 6 inches and check that the ground is level. Fill with concrete for the sauna foundation and check its level. Leave to cure.
Build a shed frame to fit on the concrete slab, using the 2-inch by 4-inch redwood lumber. At the top of the gable, the structure should be just 6 feet high. Leave space for a door in the center of one end. Bolt the frame to the foundation.
Attach redwood tongue-and-groove lumber to the outside of the frame; tongue-and groove gives a tighter fit, so less heat will be lost from inside the sauna, and redwood is waterproof.
Cut and fit plywood on the roof and nail in place; don’t use treated plywood as the chemicals involved could cause problems once the sauna is working. Cover with redwood and nail in place.
Fill the spaces between the studs with roll insulation and then cover with tongue-and-groove redwood for the interior walls. Make an opening 6 inches by 6 inches through the wall near the roofline for ventilation.
Cover the floor in sanded tongue-and-groove redwood pine, leaving one corner near the door uncovered; this is where the sauna stove will sit. Screw fireproof cement particle board to the walls going outward from the corner, extending to the edge of the concrete floor area and 3 feet high for protection.
Place the stove in position on the concrete and mark where the chimney will meet the roof. Cut through the roof where you've marked. Fit the chimney in place on the stove and extend the chimney through the hole to the outdoors. Nail flashing in place around the chimney on the outside of the sauna roof to prevent water entering.
Measure the inside length of the sauna. Build a frame of the length and 2 feet wide by 2 feet high using 2-inch-by-4-inch lumber. Insert supports for the frame on all four sides at 12-inch intervals.
Screw the frame to the walls of the sauna. Cut and sand more lumber to the length of the frame. Screw in place, leaving 1/2 inch between the pieces of wood to create a bench. Countersink the screws carefully.
Measure the dimensions of the doorway and build a frame for the door, making it 2 inches shorter than the height of the doorway. Cut and screw tongue-and-groove redwood to the outside and hang in place, leaving the gap at the bottom of the door for ventilation. Drill a hole and fit the latch to the door and frame.
Be sure to carefully countersink all the screws used inside the sauna, or you could end up with your bare skin against very hot metal.