How to Design a Backyard Sauna

The decisions that matter most when designing a permanent outdoor sauna for your home.

A backyard sauna can be remarkably simple.

A room. A heater. Stones. Benches. Water.

But designing a good sauna requires thinking about considerably more than where to put a hot wooden box.

Where does it sit on the property? What direction does it face?

What will you see from the upper bench?

Where will you step when you leave the heat?

How many people actually need to fit inside?

Where are your feet relative to the stones?

How will fresh air and löyly move through the space?

Where will water go?

How will the building handle a January in the Pacific Northwest?

These decisions affect not only how the sauna looks, but how it feels to use for the next several decades.

If you're thinking about building a permanent backyard sauna, here's where we'd start.

Start with how you want to sauna

Before choosing dimensions, siding, windows or a heater, think about how you'll actually use the space.

Is this primarily a sauna for one or two people?

Will your family use it together?

Do you regularly have friends over?

Do you want enough room to lie down?

Will you cold plunge between rounds?

Do you imagine stepping outside onto a small porch, or creating an entire area for cooling down?

These questions establish what the sauna actually needs to do.

It's easy to start with:

“I have room for an 8 × 8 building.”

We'd rather start with:

“What kind of sauna experience are we trying to create?”

Then design the building around it.

Choose the site carefully

Where the sauna sits on your property is one of the most consequential decisions you'll make.

Once a permanent sauna is built, you're probably not moving it.

Think beyond simply finding an empty patch of yard.

Consider the path from your house.

Think about privacy when you're moving between the sauna and a cold plunge or shower.

Look at where water naturally moves across the property.

Consider trees, existing structures and property lines.

Think about how electrical service will reach the sauna.

And then stand where the upper bench will eventually be and look around.

What do you want to see?

Maybe it's a cedar tree.

A garden.

The forest behind your property.

The sunset.

Or maybe the important thing is what you don't see: your neighbor's kitchen window.

A window can be positioned specifically to frame a view from the upper bench while maintaining privacy from the rest of the property.

That's the difference between placing a sauna in a backyard and designing a sauna for a backyard.

Design from the inside out

This is one of our fundamental principles.

Don't begin with what the sauna should look like from outside.

Start with the people inside it.

Establish where they'll sit.

Then establish where their feet will be.

Then determine the ceiling height.

Then locate the heater and stones.

Then consider ventilation.

Then doors and windows.

The exterior architecture can develop around those decisions.

This is also why we generally prefer square and rectangular sauna rooms. They give us considerably more freedom to establish the interior geometry first and then build an appropriate structure around it.

The building should conform to the sauna experience—not the other way around.

Don't make it bigger just because you can

Bigger isn't automatically better.

Every additional cubic foot of sauna needs to be heated.

Larger rooms generally require larger heaters, more material, more energy and more time to reach temperature.

At the same time, making a sauna too small creates its own compromises.

You need enough room for proper bench depth and elevation, heater clearances, circulation and comfortable distance between bathers and the heater.

So rather than asking how large a sauna you can fit, ask how much room the people using it actually need.

A couple who usually saunas alone may still want enough bench length to lie down or enough space for a few friends.

A family may need substantially more seating.

The right size isn't the smallest or largest sauna you can build.

It's the smallest room that comfortably creates the experience you want.

Get the benches high

One of the most common sauna design mistakes happens before anyone ever turns on the heater.

The benches are too low.

Heat rises.

That means the upper portion of a sauna is considerably hotter than the lower portion.

Traditional Finnish sauna design responds to this by putting the bathers high in the room.

A useful principle is often summarized as:

Feet above the stones.

Your upper bench should place your body comfortably within the hotter upper portion of the sauna, with the foot bench elevated rather than leaving your feet down near the cooler floor.

This is why ceiling height, bench height and heater selection need to be considered together.

You can't properly design one without thinking about the others.

Give the heater some breathing room

The heater isn't furniture that gets squeezed into whatever corner is left over.

It is one of the central elements of the room.

It needs appropriate clearances from combustible materials according to the manufacturer's requirements. Where space is limited, a properly designed non-combustible heat shield (such as a tile) can sometimes reduce required safety clearances while also adding thermal mass to the room. Any reduction in clearance should follow the heater manufacturer's specifications and applicable code.

But clearance is only part of the equation.

We also think about the heater's relationship to the people using the sauna. Sitting immediately beside a hot heater can expose one side of your body to uncomfortable radiant heat.

Give the heater enough room to do its job without dominating the experience.And think about the stones, not just the kilowatt rating.

In a traditional sauna, you're not simply heating air.

You're heating a mass of stone so that you can throw water on it.

Which brings us to one of the most important parts of the room.

Design for löyly

Water belongs on sauna stones.

When water hits properly heated stones, it creates löyly—the wave of steam and heat that moves through the sauna.

That means a sauna should be designed around what happens when water enters the room.

Where does the löyly travel?

Where are the bathers sitting relative to it?

How high are they?

How does fresh air move through the room?

Where does moisture go afterward?

These aren't separate questions.

They're all part of designing the environment.

A sauna isn't simply a room that reaches a certain temperature.

It's a room designed for heat, water, air and people.

Ventilation needs to be intentional

A sauna needs fresh air.

But gaps around a door or cracks in a structure aren't a ventilation system.

Good sauna ventilation considers where fresh air enters, how it mixes with the heated air in the room and how stale, humid air leaves.

The exact approach can vary depending on whether the sauna uses an electric or wood-burning heater and how the room is constructed.

What's important is that ventilation is designed intentionally rather than discovered accidentally after the sauna is finished.

Air leakage and ventilation are not the same thing.

Think about water before you build

Water is part of sauna.

You're throwing it on the stones.

People are sweating.

You may be showering nearby.

And outside the building, if you're in Western Washington, water is arriving from the sky for a significant portion of the year.

So think about where all of it goes.

The site should drain appropriately.

The structure should be separated from wet ground.

Exterior walls and roofing should shed weather.

Interior assemblies should manage heat and moisture.

And the sauna itself should be designed so normal use doesn't create a moisture problem.

This is one reason we build our permanent outdoor saunas as buildings rather than treating them like oversized pieces of outdoor furniture.

Build the envelope for the climate

A sauna creates an unusual environment.

You might be trying to maintain close to 190°F inside while it's 40°F and raining outside.

That's an enormous temperature difference across a relatively thin wall.

The walls and ceiling therefore matter.

For the outdoor saunas we build in the Pacific Northwest, that means thinking about insulation, foil vapor control, an interior air gap and an exterior wall and roof assembly designed for the weather.

The heater creates the heat.

The building has to hold it.

A powerful heater can compensate for a poorly designed structure to a point.

We'd rather design the structure correctly in the first place.

Start with the foundation

All of this eventually has to sit on something.

A finished sauna contains more weight than it might appear to from the outside: framing, roofing, siding, interior wood, benches, glass, people and a heater carrying a substantial mass of stone.

For the permanent outdoor saunas we build, we use concrete piers to create intentional structural bearing points while elevating the wood structure away from wet ground.

The exact foundation appropriate for a project depends on the site, structure and local requirements.

The important thing is to make the foundation part of the design from the beginning.

A permanent sauna deserves a permanent approach to what supports it.

Plan the electrical early

If you're building an electric sauna, don't wait until the structure is finished to call an electrician.

Most full-size electric sauna heaters require a dedicated 240V circuit, and the electrical requirements should be considered while you're deciding where the sauna goes.

How far is the electrical panel from the sauna?

Does the panel have sufficient capacity?

Where will the heater be located?

Where will the controls go?

Do you want interior or exterior lighting?

Are you adding a cold plunge, outdoor shower or other equipment nearby?

These decisions can affect both the design and the cost of the project.

Planning them early is considerably easier than figuring them out after the walls are closed.

Design the transition out of the heat

Some of the best moments in sauna happen outside the sauna.

You open the door.

Cold air hits your skin.

Steam rises off your body.

Maybe you walk to a plunge.

Maybe you take a shower.

Maybe you sit on the porch for ten minutes and listen to the rain.

That transition deserves to be designed too.

Think about where the door opens.

Whether you want a covered area outside.

Where towels hang.

Where robes go.

Whether the path to the cold plunge is comfortable barefoot.

Whether you have somewhere to sit between rounds.

Whether you're protected from your neighbors while you're cooling down.

The sauna experience doesn't stop at the door.

Let the architecture belong to the property

Finally, think about what you're adding to your backyard.

A permanent outdoor sauna doesn't need to look like a stereotypical sauna.

It doesn't need a giant glass wall.

It doesn't need to announce itself.

Look at the house.

The landscape.

The trees.

The slope.

Existing materials.

Sightlines.

Sunset.

Privacy.

Sometimes the right answer is dark siding that disappears against the forest.

Sometimes it's natural cedar that will weather with the landscape.

Sometimes it's a carefully positioned window that turns an ordinary view into something you notice every time you sit down.

The goal isn't to put an impressive object in the backyard.

It's to build something that feels like it was always supposed to be there.

Build the experience first

There are hundreds of decisions involved in designing a custom backyard sauna.

But most of them become easier when you get the order right.

Start with the people.

Then the sauna experience.

Then the benches, stones, heat, air and water.

Then the building.

Then the landscape around it.

Not the other way around.

Because the best backyard sauna isn't necessarily the biggest, hottest or most expensive one.

It's the one that makes you want to walk outside, open the door and use it again tomorrow.

Sauna is a return to self. A welcome home.