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Backyard Shed → Backyard Sauna
Transform a basic backyard shed into a fully functional sauna with proper insulation, vapor barriers, cedar paneling, an electric or wood-burning heater, and ventilation for a personal wellness retreat.
Cost Range
$3,000 – $12,000
Timeline
2–6 weeks
Materials Cost
$4,645
Permits Cost
$350
Evaluate your shed for structural integrity, size, and proximity to electrical service. A sauna needs a minimum interior footprint of 4x6 feet for a two-person setup and 6x8 feet for four people. Check for rot, leaks, and a solid floor. The shed should be level and on a stable foundation — concrete pad, pavers, or pressure-treated skids.
Estimated time: 2 days
If the shed has exposed studs, install R-13 to R-19 mineral wool insulation in the walls and R-19 to R-25 in the ceiling. Mineral wool is preferred over fiberglass for saunas because it handles heat and moisture better. Insulate the floor with rigid foam board (R-10 minimum) to prevent heat loss to the ground. Every gap and seam must be tight — heat escapes through the smallest openings.
Estimated time: 3 days
Apply a continuous aluminum foil vapor barrier over the insulation on all walls and the ceiling. The foil goes on the warm side (facing the sauna interior) to reflect radiant heat back into the room and prevent moisture from reaching the insulation and framing. Overlap all seams by 2-3 inches and seal with high-temperature aluminum tape. This step is critical — without a proper vapor barrier, moisture will rot the framing within a few years.
Estimated time: 2 days
Line the walls and ceiling with tongue-and-groove cedar planks. Western red cedar is the traditional choice — it resists rot, smells wonderful when heated, stays cool to the touch, and does not release sap. Install horizontal furring strips (1x2 lumber) over the vapor barrier to create an air gap, then nail the cedar planks to the furring strips. Do not use any sealant, stain, or finish on interior cedar — heat will cause chemicals to off-gas.
Estimated time: 3 days
Choose between an electric heater (most common, easiest to install, requires 240V circuit) or a wood-burning stove (traditional feel, no electrical required, needs a chimney). Size the heater to your room volume — most manufacturers provide a cubic footage rating. An electric heater for a small shed sauna (200-300 cubic feet) typically needs a 4.5 to 6 kW unit running on a dedicated 240V, 30-amp circuit installed by a licensed electrician. Mount the heater on the wall per manufacturer instructions and surround it with sauna stones.
Estimated time: 3 days
Build two-tier benches from cedar or other sauna-grade wood (aspen and alder also work well). The upper bench should be 36-42 inches from the ceiling — this is where the hottest air collects. The lower bench sits 18 inches below the upper bench. Use stainless steel screws countersunk below the surface or hidden underneath to avoid burns. Bench slats should be spaced 1/2 inch apart for air circulation.
Estimated time: 2 days
A sauna needs both an intake vent (low on the wall near the heater) and an exhaust vent (high on the opposite wall). These can be simple adjustable wood vents — no fan needed, as the heat differential creates natural airflow. Install a sauna-grade door — a tempered glass door is popular because it lets in light and feels less claustrophobic. The door must swing outward for safety. Add a simple thermometer and hygrometer inside.
Estimated time: 2 days
Seal the exterior of the shed with weather-resistant stain or paint to protect against rain and snow. Ensure the roof is watertight. Add exterior lighting along the path to the sauna. Place a small deck or platform outside the door for cooling off. Add hooks inside for towels and a bucket and ladle for pouring water on the stones.
Estimated time: 2 days
| Material | Est. Cost | Required |
|---|---|---|
| Mineral Wool Insulation (R-13 walls, R-19 ceiling) | $400 | Required |
| Rigid Foam Board Insulation (floor) | $150 | Required |
| Aluminum Foil Vapor Barrier | $80 | Required |
| High-Temperature Aluminum Tape | $25 | Required |
| Western Red Cedar Tongue-and-Groove Paneling | $1,200 | Required |
| Furring Strips (1x2 lumber) | $60 | Required |
| Electric Sauna Heater (4.5-6 kW) with Stones | $800 | Required |
| 240V Electrical Circuit Installation (by electrician) | $800 | Required |
| Cedar Bench Lumber | $400 | Required |
| Stainless Steel Screws and Hardware | $50 | Required |
| Tempered Glass Sauna Door | $500 | Optional |
| Intake and Exhaust Vents | $40 | Required |
| Sauna Bucket, Ladle, Thermometer | $60 | Optional |
| Exterior Weatherproofing Stain | $80 | Required |
Required for the new 240V dedicated circuit. Your electrician typically pulls this permit.
$150
Some jurisdictions require a permit for adding a heater or modifying an outbuilding. Check with your local building department.
$200