Why Convert a Shed Instead of Buying a Prefab Sauna?
Prefabricated outdoor saunas cost $4,000 to $15,000 for a basic 2-4 person unit, and premium models with change rooms and covered porches can run $20,000 or more. Meanwhile, a used shed in decent condition costs $500 to $2,000, and the conversion materials cost $2,000 to $3,500. Total investment: under $5,000 for a sauna that performs identically to units costing three times as much.
The key difference is labor — you are doing the work yourself. But a shed-to-sauna conversion is one of the most approachable DIY projects because it involves basic carpentry (framing, insulation, paneling) and one electrical connection. No plumbing, no foundation work, no roofing.
What Size Shed Do You Need?
A sauna does not need to be large. In fact, smaller is better — a smaller volume heats up faster, uses less energy, and maintains temperature more efficiently.
Solo or couples use: 4x6 feet interior minimum. A small garden shed works perfectly.
Family or social sauna (3-4 people): 6x8 feet interior. A standard 8x10 shed provides this after insulation reduces the interior dimensions.
Ceiling height: 7 feet is ideal. The heater needs space below the benches, and you need clearance above the upper bench. Most standard sheds meet this requirement.
The Build in 5 Steps
Step 1: Insulate Everything ($400-$600)
Insulation is the most important part of the build. Without it, your heater works overtime and the sauna never reaches proper temperature. Use mineral wool batts (R-13 in walls, R-19 in ceiling) — mineral wool handles heat and moisture better than fiberglass and does not melt or off-gas at sauna temperatures. Insulate the floor with rigid foam board (R-10 minimum) to prevent heat loss to the ground.
Step 2: Vapor Barrier ($80-$120)
Apply aluminum foil vapor barrier over all insulated surfaces, with the shiny side facing inward toward the sauna. This reflects radiant heat back into the room and prevents moisture from reaching the insulation and framing. Overlap seams by 2-3 inches and seal with high-temperature aluminum tape. Skip this step and your framing will rot within 2-3 years.
Step 3: Cedar Paneling ($800-$1,500)
Line the walls and ceiling with tongue-and-groove western red cedar. Cedar is the traditional sauna wood because it resists rot, stays cool to the touch even at high temperatures, smells wonderful when heated, and does not release sap. Install horizontal furring strips over the vapor barrier first, then nail the cedar planks to the furring strips. Never apply stain, sealant, or finish to interior sauna cedar — the heat will cause any coating to off-gas.
Step 4: Electric Heater and Benches ($800-$1,500)
For a small shed sauna, a 4.5 to 6 kW electric heater is sufficient. This requires a dedicated 240V, 30-amp circuit installed by a licensed electrician (budget $500-$800 for the electrical work). Mount the heater per manufacturer instructions and fill it with sauna stones. Build two-tier benches from cedar — the upper bench 36-42 inches from the ceiling, lower bench 18 inches below. Use stainless steel screws countersunk below the surface to prevent burns.
Step 5: Ventilation and Door ($200-$500)
Install an intake vent low on the wall near the heater and an exhaust vent high on the opposite wall. No fan needed — heat differential creates natural airflow. Install a tempered glass sauna door or a solid cedar door that swings outward for safety. Add a thermometer and hygrometer inside.
Budget Breakdown
Shed (used, decent condition): $500 to $2,000
Mineral wool insulation + rigid foam: $400 to $600
Aluminum foil vapor barrier + tape: $80 to $120
Cedar tongue-and-groove paneling: $800 to $1,500
Electric sauna heater + stones: $500 to $900
Electrician (240V circuit): $500 to $800
Cedar bench lumber + hardware: $200 to $400
Door, vents, accessories: $200 to $500
Total: $3,180 to $6,820
Health Benefits Worth the Investment
Regular sauna use (3-4 times per week) has been linked to improved cardiovascular health, reduced stress, better sleep, muscle recovery, and skin health. A backyard sauna pays for itself in skipped gym memberships and spa visits within the first year.
For the complete step-by-step build with detailed instructions, check out our shed to backyard sauna conversion guide. Use our cost calculator for a personalized estimate.
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