Your contractor just said yes to building your sauna. Good. Now they need something to build from.

This is where a lot of sauna projects stall. The homeowner has a vision — maybe some Pinterest photos, a rough sketch, a heater they found online. The contractor has the tools and the crew. But nobody has an actual set of construction documents that accounts for everything a sauna requires.

A sauna isn't complicated to build. But it has specific requirements that differ from standard construction in ways that aren't intuitive. If your contractor doesn't get the right information upfront, they'll make assumptions based on how they normally build things. And those assumptions will cost you performance, comfort, or both.

Here's exactly what your contractor needs.

1. Dimensioned Floor Plan and Elevations

This is the foundation. Your contractor needs a floor plan showing the interior dimensions of the sauna room — length, width, and ceiling height. They also need elevation drawings (front, side, and interior views) showing bench positions, door placement, heater location, and ventilation openings.

The dimensions matter more than you'd think. A sauna that's 6x8 feet with an 8-foot ceiling has 384 cubic feet of interior space. At 1 kW per 45 cubic feet, that requires roughly an 8.5 kW heater. Change the ceiling height to 7 feet and the volume drops to 336 cubic feet — now a 7.5 kW heater works. These numbers cascade through the entire design.

Ceiling height also determines bench placement. The upper bench should sit 40-48 inches below the ceiling, putting the bather's head in the hottest zone (170-200°F). In a 7-foot ceiling sauna, that means the upper bench is about 36-44 inches off the floor. In an 8-foot ceiling, it's 48-56 inches off the floor. Your contractor won't know this unless you tell them.

2. Complete Materials List With Quantities

Don't make your contractor figure out what to buy. Give them a list that includes:

Framing and structure: Stud dimensions, spacing, header sizes for the door opening. Standard 2x4 framing at 16 inches on center works for most saunas, but the ceiling may need 2x6 or 2x8 joists depending on insulation requirements.

Insulation: R-13 to R-21 for walls, R-30 or higher for the ceiling. The ceiling spec is critical — heat rises, and the ceiling is your biggest source of heat loss. Mineral wool (like Rockwool) is preferred over fiberglass because it handles higher temperatures without off-gassing.

Vapor barrier: Aluminum foil vapor barrier, specified for the warm side of the insulation. This is the single most important item to get right. In a sauna, the vapor barrier goes between the insulation and the interior paneling — the opposite of where it goes in standard residential construction. More on this below.

Interior paneling: Species (cedar, alder, hemlock, etc.), dimensions, board footage. Include the ceiling. Specify tongue-and-groove profile and whether it's installed horizontally or vertically.

Bench lumber: Species, dimensions, and linear footage. Benches are typically 2x4 or 2x3 slats with gaps for air circulation. The frame is usually 2x4 construction.

Door: Sauna doors are typically smaller than standard doors — 24-28 inches wide, with a window. Tempered glass. The door should swing outward for safety.

Hardware, trim, and accessories: Hinges, handle (wood, not metal — metal gets too hot), any trim pieces, vent covers.

Quantities matter. Your contractor shouldn't have to count boards from a drawing. Give them the number.

3. Heater Selection and Electrical Specifications

Your contractor needs to know exactly what heater you're installing and what electrical work it requires.

For electric heaters in the 6-9 kW range (which covers most residential saunas), the typical requirement is a dedicated 240V circuit with 40-50A service. The heater manufacturer's manual will specify exact wire gauge, breaker size, and conduit requirements.

What to include for your contractor:

• Heater make, model, and kW rating
• Required voltage (240V for most residential units)
• Required amperage and breaker size
• Wire gauge specification
• Whether the heater is hardwired or plug-in
• Location of the heater in the room (always on the wall, with manufacturer-specified clearances to benches, walls, and ceiling)
• Control panel location (inside or outside the room, depending on model)
• If using a Harvia Xenio WiFi system or similar digital controller, specify the control unit mounting location

The electrician needs to run this circuit from the main panel. It's a dedicated line — no sharing with other circuits. This is something to plan before framing starts, not after.

4. Ventilation Layout

This is where contractors go wrong most often, because sauna ventilation is counterintuitive.

In standard construction, HVAC logic says seal it up and control airflow mechanically. In a sauna, you need passive intake and mechanical exhaust working together to keep the air fresh.

Fresh air intake: A vent opening (typically 4-6 inches in diameter) placed on the wall near the heater, 6-12 inches below the ceiling. The heater warms incoming air immediately, so it doesn't create a cold draft.

Mechanical exhaust: A vent with a small fan on the opposite wall, below the foot bench level. This pulls stale, cooler air out from the bottom of the room while fresh heated air enters from the top.

Airflow rate: 20-25 CFM per person the sauna is designed for. A 2-person sauna needs 40-50 CFM of air exchange.

Your contractor will want to skip ventilation or put vents where they'd normally go in a bathroom. Don't let them. Without proper ventilation, the sauna air gets heavy and stale after one round. You'll feel it. It's the difference between a sauna you want to sit in for 20 minutes and one you want to leave after 10.

Include a ventilation diagram in your plans — a simple drawing showing intake location, exhaust location, duct routing if applicable, and fan specification.

5. Construction Sequence Notes

A sauna goes together in a specific order, and some steps can't be reversed. Give your contractor a build sequence:

1. Frame the room. Standard framing, nothing unusual here.
2. Rough-in electrical. Run the heater circuit, control wiring, and any lighting circuits before insulating.
3. Cut ventilation openings. Intake and exhaust holes through the framing/sheathing.
4. Insulate. Walls and ceiling to specified R-values.
5. Install vapor barrier. Aluminum foil on the warm side (facing the interior), sealed at all seams and penetrations with foil tape. This step is critical — any gaps allow moisture into the wall cavity.
6. Install furring strips. These create an air gap between the vapor barrier and the paneling, which helps the wood dry between uses.
7. Install interior paneling. Ceiling first, then walls.
8. Build and install benches. Upper bench 40-48 inches below ceiling, lower bench 16-18 inches below upper.
9. Install door.
10. Install heater and make electrical connections.
11. Install vent covers and exhaust fan.
12. Finish trim and accessories.

The vapor barrier step is the one that gets skipped or done wrong most often. In residential construction, the vapor barrier goes on the exterior. In a sauna, it goes on the interior — between the insulation and the paneling. If your contractor installs it in the wrong position, moisture from the sauna will condense inside the wall cavity. You won't see it until mold shows up months or years later.

What Your Contractor Doesn't Know About Saunas

This isn't a criticism. Contractors are great at building things. But saunas have quirks that go against their training:

The vapor barrier goes on the wrong side. Already covered this, but it's worth repeating. Every contractor's instinct will be to put it on the exterior side. Specify it clearly in the documents and explain why.

Ventilation feels wrong to them. Cutting holes in an insulated room to let air in and out feels like a mistake. It's not. A sauna without ventilation is a sauna nobody wants to use twice.

Bench height isn't arbitrary. They'll want to build benches at a "normal" seating height — 17-18 inches off the floor, like a chair. In a sauna, the upper bench needs to be much higher to put you in the heat zone.

Metal gets hot. No exposed screws or nails on bench surfaces. No metal door handles. Any metal the bather might touch will be at 170-200°F.

The door swings out. Always. For safety — if someone gets lightheaded, they need to fall against the door to open it, not push against it.

How to Get These Documents

If you're a DIY designer, you can put these together yourself using our resources. But the details matter, and getting one thing wrong (like vapor barrier placement or heater sizing) can mean an expensive fix later.

We produce complete sauna construction packages at Tahoe Sauna Company through our remote design service. The package includes everything listed above — dimensioned drawings, materials list, heater specs, ventilation layout, and construction notes — formatted so your contractor can build from them directly.

We also have a resource specifically written for contractors who've been asked to build their first sauna. If your contractor wants to understand the why behind these specifications, that's a good starting point. And if you want to understand the mistakes that come up most often, check out our guide on sauna building mistakes contractors make.

The goal is simple: give your contractor everything they need so they can build a sauna that actually works. Not a hot room. A sauna.