Converting a room into a sauna means building a new insulated, vapour-sealed shell inside the existing room — not simply lining the walls you already have. You strip back to the studs or build a new inner frame, insulate, install a foil vapour barrier, cut ventilation openings, clad in non-resinous softwood, build benches and install a heater on a dedicated 240V circuit.
It is a genuinely achievable project for a competent DIYer, and it is the most common way a custom sauna gets built. This guide sets out the sequence, the details that must be right, and what it costs.
Step 1: Choose the right room
Not every room converts well. Assess candidates on five criteria.
Ceiling height. You need about 7'6" of existing height to finish at 7 feet with an insulated dropped ceiling. Below that you will be working toward 6'8", which is workable but tight.
Floor. Concrete or tile is ideal. A wood subfloor works with a suitable finished floor over it. Carpet must come out entirely.
Distance to the panel. Every foot of 240V run costs money, especially through finished construction.
Distance to a shower. The single best predictor of how often the sauna gets used. Twenty steps is good; two floors is not.
A ventilation route. The exhaust has to discharge somewhere sensible — ideally an exterior wall.
Best candidates, in order:
- A basement room or partitioned area — space, concrete floor, often near a drain
- Part of an oversized bathroom — already waterproofed, next to a shower
- A garage bay — space, tolerance for construction, often existing 240V
- A walk-in closet or small spare room — viable for a small sauna
- A utility or laundry room — often has drainage and an exterior wall
Any room on an upper floor with no drainage and a carpeted wood subfloor; a room with no ventilation route at all; a room with a ceiling under 6'6".
Step 2: Check the electrical before anything else
Free, ten minutes, and it determines whether the project is affordable.
Walk to the panel. Count free breaker slots. Read the main breaker rating. Measure the distance to the room.
| Heater | Typical breaker |
|---|---|
| 4.5 kW | 20–30 A |
| 6 kW | 30–40 A |
| 8 kW | 40–50 A |
| 9 kW | 50 A |
Adding a sauna circuit requires a subpanel ($1,000–$2,500) or a service upgrade ($2,500–$6,000). That cost has nothing to do with the sauna and can exceed the price of the conversion.
→ Custom Sauna Electrical Requirements
Step 3: Strip and prepare
Remove everything down to the framing on the walls and ceiling that will form the sauna: drywall, existing insulation if it is not suitable, carpet, trim, outlets and fixtures.
Why you cannot just line over drywall: a sauna's shell must be insulated to the right value, must have a continuous foil vapour barrier on the warm side, and must have the cladding fixed to battens with an air gap in most designs. Building over existing drywall traps a layer that will absorb moisture, and the vapour barrier ends up in the wrong place.
If you cannot strip back — a rented space, or a wall you must not disturb — the alternative is building a new inner frame inside the room, standing off the existing wall. You lose 5–6 inches per wall, but the sauna's shell is then complete and independent.
Deal with existing problems first. Damp, efflorescence on a basement wall, or any sign of water ingress must be resolved before the sauna goes in.
Remove or relocate anything that cannot live in a sauna: electrical outlets, switches, plumbing, ducts, and lighting.
Step 4: Frame and drop the ceiling
Frame any new walls at 16" centres, with blocking where benches, the heater, the guard rail and the door frame will fix. Getting the blocking in now saves a lot of frustration later.
Drop the ceiling to 7 feet. Frame it as you would a floor structure, insulate above it, and carry the vapour barrier continuously across the wall-to-ceiling junction. The void above is where the exhaust duct runs.
Frame the door opening for an outward-opening door.
Frame the ventilation openings — inlet low near where the heater will go, outlet on the opposite wall.
Check everything is plumb, square and level. Cladding shows every error.
Step 5: Insulate
| Element | Target |
|---|---|
| Walls | R-13 minimum, R-15 better |
| Ceiling | R-20 minimum, R-26 better |
| Floor over unheated space | R-11 or better |
| Against an exterior wall in a cold climate | Increase both |
Use mineral wool or fibreglass batts. Do not use foam board as the primary insulation inside a sauna shell without checking its temperature rating.
Fill completely, without compressing. Compressed insulation loses value; gaps are thermal bridges.
Insulating a basement foundation wall is worth doing properly — an uninsulated concrete wall adds enormously to the heater requirement, and insulating it is far cheaper than the extra kilowatts, the bigger circuit and the permanently higher running cost.
Step 6: The vapour barrier
Foil, not polyethylene. On the warm side of the insulation. Every wall and the ceiling, no exceptions. All seams overlapped and taped with foil tape. Sealed around every penetration — vents, the light, the heater's cable entry, the door frame.
What happens if you get it wrong: hot moist air migrates into the wall cavity, cools, condenses inside the insulation and framing, and rots the structure. It is invisible for a couple of years, and then it is a substantial repair.
If anything ever needs opening up, you will be glad to know exactly what is behind the boards.
Step 7: Ventilation
Inlet low on the wall behind or beside where the heater will be, or in the floor under it. Adjustable outlet on the opposite wall, low to mid-height. Roughly 4–6 square inches of inlet per kW of heater.
Where the exhaust discharges matters in a conversion. Options, best first:
- Duct to an exterior wall
- Duct into an existing mechanical extract path
- Into a well-ventilated adjacent space such as a garage
- As a last resort, into the wider room with a dehumidifier running there
Never into a sealed cupboard, a finished hallway or a bedroom. Use grilles rated for sauna temperature — plastic will deform.
→ Custom Sauna Ventilation Requirements
Step 8: Clad and build
Battens over the vapour barrier, typically 20 × 45 mm, giving an air gap behind the cladding. Run them perpendicular to the cladding direction.
Cladding: non-resinous softwood, unfinished. Cedar, Nordic spruce, hemlock or thermally modified aspen. Fix with hidden nails through the tongue, leaving a small expansion gap at floor and ceiling.
Benches: upper at 42–48 inches, lower at 18–20 inches, upper at least 72 inches long if anyone will lie down. Hidden fixings only — no exposed screw heads anywhere skin touches. Slats gapped 3–8 mm.
Floor: tile, sealed concrete or sauna vinyl, with a removable duckboard over it. Never carpet. Note that tile adds roughly 1.5 kW per square metre to the heater requirement.
Door: outward-opening, non-latching, tempered glass, wooden handle, roughly ½–¾ inch gap underneath.
Lighting: rated for the environment, indirect, never in the eyeline of someone lying on the upper bench.
→ Best Wood for Custom Saunas · How to Design a Custom Sauna
Step 9: Heater and electrical
Size the heater from the finished interior volume ÷ 45–50, plus adders: 0.5 kW for a glass door, 1.5–2 kW per m² of larger glass, 1.5 kW per m² of tile or uninsulated masonry.
Mount it at the manufacturer's specified height with every clearance verified against the bench positions.
Sensor in the manufacturer's specified position, out of the incoming air path.
The electrician runs the dedicated circuit — ideally roughed in at step 4, before the walls close — and makes the final connection with an accessible disconnect outside the hot room. Then it is inspected.
→ Custom Sauna Heater Buying Guide
Step 10: Commission
- Stack the stones loosely, largest at the bottom, with visible air gaps
- First firing with nobody inside, well ventilated, for an hour or two to burn off manufacturing residues. Expect a smell.
- Check the room reaches temperature in a sensible time — 30–50 minutes
- Tune the outlet vent until the room feels right
- File the documentation: manuals, warranty, electrician's invoice, permit sign-off, and the photographs of the vapour barrier
What a conversion costs
US market ranges, not store prices, for a 5' × 6' room.
| Line | Range |
|---|---|
| Strip-out and disposal | $200 – $800 |
| Framing and blocking | $400 – $1,500 |
| Dropping the ceiling | $300 – $1,200 |
| Insulation | $250 – $700 |
| Foil vapour barrier and tape | $150 – $400 |
| Battens and cladding | $1,600 – $4,500 |
| Benches | $600 – $2,200 |
| Door | $500 – $1,500 |
| Floor finish and duckboard | $300 – $1,200 |
| Ventilation | $150 – $600 |
| Lighting | $200 – $700 |
| Heater, stones, controls | $1,000 – $2,600 |
| Electrical | $500 – $1,500 |
| Permit | $100 – $400 |
| Labour, if hired | $3,000 – $10,000 |
| DIY total | $6,250 – $18,300 |
| With labour | $9,250 – $28,300 |
→ How Much Does a Custom Home Sauna Cost?
How long a conversion takes
| Stage | DIY | Contractor |
|---|---|---|
| Planning and permit | 2–5 weeks | 2–5 weeks |
| Strip-out | 1 weekend | 1 day |
| Framing and ceiling | 1–2 weekends | 2–3 days |
| Electrical rough-in | — | 1 day |
| Insulation and vapour barrier | 1 weekend | 1–2 days |
| Ventilation openings | Half a weekend | Half a day |
| Cladding | 2–3 weekends | 3–5 days |
| Benches | 1–2 weekends | 1–2 days |
| Door, trim, lighting | 1 weekend | 1 day |
| Heater and final connection | — | 1 day |
| Inspection | 1–2 weeks | 1–2 weeks |
| Elapsed | 8–16 weeks | 4–8 weeks |
Sequence notes that save weeks:
- Apply for the permit and book the electrician at the very start, not when you are ready for them
- Get the circuit roughed in while the walls are open
- Order the heater early; you need its manual for clearances and the sensor position before you build the benches
- Order cladding early too, and check the lengths will get into the room
Reaching the insulation stage and discovering the electrical circuit was never planned. Rough it in at step 4.
Conversion mistakes to avoid
Lining over existing drywall. Traps a moisture-absorbing layer and puts the vapour barrier in the wrong place.
Polyethylene instead of foil. Or foil with untaped seams. The most consequential error available.
Leaving the ceiling at its existing height. A 9-foot ceiling is 29% more volume than 7 feet, forever.
Not resolving existing damp first. A sauna makes a moisture problem worse.
Skipping ventilation because the room is small or because there is nowhere obvious for the exhaust to go. Solve it; do not omit it.
Leaving carpet or an unsuitable floor.
Ordering the heater before finalising the glass and floor finish. Both are large adders.
Doing the 240V connection yourself. Licensed work; voids warranties and can invalidate insurance.
→ DIY Sauna vs Professional Installation
Converting specific room types
A bathroom. The best location for usage and the tightest for space. Usually means removing a bath, a linen closet or part of a vanity. The room is already waterproofed and drained, but the sauna still needs its own ventilation path rather than sharing an extractor sized for a shower.
A walk-in closet. Viable at 4' × 6' or larger. The two problems are ventilation — closets rarely have an exterior wall — and the door, since a closet door is almost always inward-opening and must be replaced.
A laundry or utility room. Often has drainage, an exterior wall and existing 240V for a dryer, which makes it one of the more practical conversions. The constraint is that you are usually taking space from a room that still has to do its original job.
A basement partition. Building a sauna as a freestanding insulated box within a larger basement, rather than lining an existing corner, is almost always the better approach — it avoids inheriting a foundation wall's moisture behaviour and it looks deliberate rather than improvised.
A garage bay. Plenty of space, tolerance for construction, often existing 240V. The main work is insulating the sauna shell properly against an unconditioned space.
A spare bedroom. Workable, but check floor loading on an upper storey, plan the ventilation route carefully, and be honest about the distance to a shower.
Frequently Asked Questions
Can you turn any room into a sauna?
Most rooms can be converted, but the good candidates have about 7'6" of ceiling height, a floor that tolerates water, a route for the exhaust to discharge sensibly, reasonable proximity to the electrical panel and — for usage — a shower nearby. Rooms on upper floors with carpeted wood subfloors, no drainage and no ventilation route are the hardest cases.
Can you convert a closet into a sauna?
Yes, if it is at least about 4' × 4' internally after the new insulated shell is built, and if the ceiling and ventilation can be resolved. A walk-in closet at 4' × 6' makes a good small sauna. Remember that framing, insulation and cladding take roughly 5–6 inches off each wall, so the finished interior is smaller than the closet you measured.
Do you need to remove drywall to build a sauna?
Ideally yes. A sauna needs insulation to the right value with a continuous foil vapour barrier on the warm side, and building over existing drywall traps a moisture-absorbing layer and puts the vapour barrier in the wrong place. Where you cannot strip back, build a new insulated inner frame standing off the existing wall instead.
How much does it cost to convert a room into a sauna?
Roughly $6,250–$18,300 doing the work yourself and hiring only an electrician, or $9,250–$28,300 with labour, for a 5' × 6' room. Cladding, benches and labour are the largest lines. Any electrical panel work — a subpanel at $1,000–$2,500 or a service upgrade at $2,500–$6,000 — sits on top and is the most common cause of a conversion going over budget.
What insulation do you use for a sauna conversion?
Mineral wool or fibreglass batts at R-13 or better in walls and R-20 or better in the ceiling, filled completely without compressing, with a foil vapour barrier taped over the warm side. Increase both where a wall is exterior in a cold climate. Insulating an uninsulated basement foundation wall is always cheaper than the extra heater capacity and larger circuit it would otherwise demand.
Room picked and panel checked?
Related guides
- How to Build a Sauna in a Basement
- How to Build a Sauna in a Garage
- How to Design a Custom Sauna
- Custom Sauna Ventilation Requirements
- How Much Space Do You Need for a Sauna?
Published by Finest Saunas