How to build your DIY backyard sauna: Step-by-step instructions
When we set out to build our first sauna, we were met with a confusing landscape with just as much mysticism and criticism as helpful information. As experienced DIY builders, we wanted to build our own sauna, not just to keep the costs down, but because we love a good project, and knew that we could produce a better end result than off-the-shelf kits. A couple of saunas and an immense amount of research later, we have honed my approach to be pragmatic above all - cut the mysticism, get the best bang for your buck, and make something that will function well and last for a long time. With the plans and resources here, you can build your own sauna, too!
The approach
Combining some common sense with a lot of best practice, we’ve tried to make things simple for DIY’ers to produce a highly functional sauna on a reasonable budget. Sauna devotees can be near religious with their dedication to philosophies and rules-of-thumb, so we can’t guarantee to make every commenter on r/sauna happy, but we did our best to make things easy and functional.
Our design
The standard sauna design that we’ll go over here uses a 6’x8’ footprint with an electric heater to maximize interior space (wood-fired stoves need much more clearance from walls and benches than electric. The 7’6 interior height is just enough to get the benches nice and high so there are no cold feet, and not too tall to be a nuisance. The single pitch roof is the easiest style for DIY builders — then adding a flat ceiling inside you get optimal flow of heat and loyly, plus easier building. Our plans feature detailed framing and finishing notes giving DIY’ers the confidence to build on their own.
Of course, the most fun part of any project is making it your own. With some design know-how, these plans can be easily modified to fit your needs of space. Or, reach out to us, and we can help you design your dream sauna.
Our choices of design and materials are meant to cover the essentials - rock solid. Of course, you’re welcome to up the level of fit and finish to suit your needs and budget. This means some huge upgrades over kit saunas that you might be tempted by. Things like full stud construction that allows for insulation, and additional height for better bench placement.
Have questions? Try out our AI SaunaBot assistant
Pre-build considerations
Beyond customizing your design, there are a handful of things to consider before you build.
Permitting: Check with your local building department if you need a permit. The easiest way to know is just to give them a call (search “Your County building department”). Typically, the small size of the building means you don’t need a permit for the building, but your electrical might.
Electrical: This is the one are where most DIYers will need some expert help, plus a permit might be required. See below for a deeper dive into electrical considerations.
Foundation: Our plan is ready to sit on a flat surface like a deck or concrete slab. If you don’t have a flat place ready to go, you’ll need to make a foundation plan.
Framing
Building the floor
Your sauna floor, and most of the framing really, is pretty straightforward — you’re pretty much just building a small shed. Our floor plan is built with pressure-treated 2x4s with 16” spacing. This is designed to sit flat on a deck or slab.
Typically, you’d use pressure-treated plywood for a floor like this, but we’ve spec’ed regular plywood here to avoid any off-gassing issues from the chemicals in the treatment. A waterproof membrane will go on top of this floor, so PT is likely okay, but chemicals are nasty, so choose what you think is best. This does mean that it’s extra important to make sure that you avoid moisture pooling around the base of your sauna from the outside.
Steps to building the sauna floor
Cut your boards to 8’ (2), 5’9 (7), and
Mark the layout on both of the 8’ boards
Check your board for crowns, laying them out crown side up
Nail everything together with hot-dipped galvanized nails
Add blocking between floor joists, this is your chance to straighten any bows and bends
Check the floor for square before nailing plywood by measuring the diagonals
Nail down the plywood
Cut and fit the insulation to the cavities, filling any gaps with spray foam
Tips
8’ lumber is probably longer than 8’, so make sure to measure!
Treat the cut ends of the pressure-treated lumber for the longest lifespan
Make sure to use hot-dipped galvanized nails for pressure treated, or screws that are rated for pressure-treated
You can use the factory-straight edges of your plywood to help keep the floor square
Mark the joist layout on the floor with a chalk line to avoid missing nails
For a perfect edge, rip the smaller piece of plywood to width after nailing it, mark the cut with a chalkline and use a straight edge or track saw to guide your cut. Or you can even clean up the edge with a router if needed
Walls
Don’t be afraid if you haven’t framed walls before, it’s pretty simple once you get the basics down! Studs are spaced at 16”, however, there are several extra studs strategically added to give solid places for the bench to be attached to and to provide nailing for your tongue and groove interior cladding. Your exact stud layout can change based on your bench layout, window location, door choice, and stove, so just make sure you stop to check for bench support and nailers before you move on to insulation.
Steps to framing the sauna walls
Work one wall at a time, framing and standing the walls
2 nails per stud, or 3 toenails
Square the walls on the ground, measure diagonals, then holding them square with braces or the sheathing
Add the second top plate after standing the walls up, this lets you overlap the plates between the end and side walls for maximum strength
Install the wall sheathing, as shown, overlapping below the bottom plate over the floor system, but not all the way to the ground
Space OSB panels ⅛” to allow for expansion
Nail every to studs every 6” on the edges and every 12” “in the field” (everywhere else)
You may need to install some blocking on the side walls to help nail the sheathing edges, especially for the top (slanted) edge
Staple up your house wrap, working bottom to top, taping all seams
Tips
There are a lot of tips and tricks to framing walls accurately and efficiently. First, work on getting the sequence down – cut and mark out your top and bottom plates, then mark the stud layout, cut all of your studs, nail it all, then stand the wall
Sheathing the walls before you stand them up can help keep them square, as the sheathing acts as continuous bracing keeping the studs where you want them. Just make sure that you have all of the overhanging pieces accounted for, like below the bottom plate onto the floor and from the side walls around to the front and back
Remember to use hot-dipped galvanized nails for nailing the bottom plate to the floor, as these will go into the pressure-treated floor
Sauna roof framing
The simple single-pitch roof is easy to frame! Using structural screws instead of toenails or hurricane clips is a great way to avoid splitting the wood or having hardware in the way of your tongue and groove. Once the rafters are up, then it’s just filling in blocking for the flat ceiling. The small span and 12” spacing mean that 2x4s are plenty strong for this roof. You can also customize here to add whatever overhang size you desire.
Mark your layout across both top plates
Install the rafters – you don’t need to worry too much about your overhangs here, cutting them after the fact will result in a nice straight fascia
Use structural screws through the rafter into the top plates, making sure to sink the screw so that it won’t be in the way of your roof sheathing
Adding minimal 3” side overhangs is easy using scrap blocks and an additional rafter nailed to the blocks
Measure and cut your front and back overhangs
Measure your front and back overhangs on the outside rafters on either side – make sure to account for 2x4 sub-fascia and your finish fascia
Snap a chalk line between these two marks
Using a speed square, draw a square line from your mark
Cut your rafters to the line
Add your sub-fascia to the newly cut rafter tails
Install roof sheathing, working from the low side of the roof to the high side
Tips
This design means your fascia will not be exactly plumb, but instead follow your rafters, but the minimal slope of the roof means that you will hardly be able to tell. For plumb fascia, you will need to rip the fascia board at an angle on the tablesaw, which not everyone will be able to do
Break your sub-fascia in the middle of two rafters, not on a rafter, to keep it the flattest. Add a block of scrap behind the joint between the pieces. Or get a couple of longer 2x4s that can span the entire distance.
The slope is pretty minimal, so a birdsmouth cut is probably not needed, another plus for the structural screws
Look for ice and water shield by the foot at your local lumber yard – make sure it's rated for high temperature for use with metal roofs
Siding and roofing
Ourdoor saunas can be clad in any number of ways, from using a simple T1-11 style shed siding (probably the most economical) to metal or even more cedar. Your choice here will have a pretty large impact on final cost.
For your walls, there are many options. From most economical to most expensive, some popular options are:
T1-11 or LP Smartside panels. Some of these even have a structural rating, meaning you don’t need exterior sheathing.
Metal. A popular choice for a good reason - durable, pretty cost-effective. Working with metal does require some specialized tools and skills.
Traditional house siding styles. There is a whole range here from Hardie to LP and even natural wood cladding like cedar. This will typically be a little bit more expensive, but a little bit easier to work with
For your roof, the choice is typically between metal and shingles. Metal might be a little bit more expensive, but it’s not a large roof!
Your choices of siding and roofing will dictate your trims, like corners, fascia, and soffit. So, we didn’t outline those items here. Ask SaunaBot questions on those, or feel free to reach out to us with questions.
Finishing the floor
Like all sauna design decisions, there are many different ways to finish the floor, each with different costs. First, the decision to include a floor drain or not. We generally think that if you are not bathing in the sauna (pouring water over yourself and thus the floor) you do not need a floor drain since the water volume will be fairly low. Some will argue in favor of a drain regardless, so we’ll leave the decision up to you. Regardless, we do recommend a waterproof floor. Options include full tile or various waterproofing methods with a removable wooden floor or mat placed on top, the latter is outlined below.
On top of the PT plywood sub-floor, cement board sealed off with a waterproof (and somewhat flexible) product like vinyl cement patcher will seal off any potential nastiness from the PT ply and make the floor waterproof. Tile is an option as well. If you’re going to tile, make sure to use an uncoupling membrane like Schulter Ditra.
Then, for the finish floor, you can build a wooden mat. This can be done using extra T&G, or additional lumber; just make sure to space it up off the floor for airflow.
Installing windows in your sauna
Unlike a shed or house, where you would use windows that are pre-built into a frame, the best way to add windows to your sauna is to make “site-built” windows. This means buying glass, and building the frame yourself. This way the frame will also be built from cedar, and not vinyl that would melt, plus you can get more insulated and stronger tempered glass insulated units. See the notes below on ordering the glass. If this all sounds like too much fuss, a glass door is a great way to let in light instead of adding windows.
Framing your window openings properly is key to avoiding headaches down the road! We have window and opening specs called out in our plans, but since this is one of the most customizable pieces of the design, we’ll put our thoughts here, too.
There are a few design choices (purely aesthetic) that are involved with the windows, so we’d actually recommend doing your finish-framing with the windows at the same time as the tongue and groove. This lets you pick your trim styling and make sure everything is nice and tight.
The basic components are the finish framing — head, sill, and jambs, and the stops, which hold the glass in. The design details that you need to choose here are mostly to do with trims and how they overlap. Our design goes with a pretty minimal aesthetic, but customize it to your taste.
Window install steps
Install the head and sill, then the jambs
Use a scrap or shim to slightly angle the sill outwards
Rip your stops to their finished width, about 1”
Nail in your exterior stops, with a bead of sealant between them and the sill/jambs
Apply 2-sided glazing tape to the inside (glass side) of the stops
Set the glass in the opening, using shims center it and set the reveal in the opening
Push the inside stops tight against the glass as you nail them
Caulk the exterior seam between the stops and the glass
Tips
Order your glass after you frame the opening to make sure that you have the correct size
To get your glass size, subtract 3/8” from every dimension of the finished opening
A pneumatic suction cup is super helpful for setting the glass
Sample glass order
Rough opening size (framing): 24 1/2” x 48”
Finish framing size: 23” x 46 1/2”
Glass size: 22 1/4” x 45 3/4”
Glass type: 1” IGU, 3/16" over 3/16”, clear safety tempered, black spacer
Sauna electrical install
Heater
If you are installing an electric sauna heater, you generally need a licensed electrician to do the work. Electric sauna stoves typically require a 240-volt connection, which involves high-voltage wiring, a dedicated circuit, proper grounding, and sometimes GFCI protection, depending on local codes. This type of installation is more complex than simply plugging in a standard appliance and must meet specific safety standards to prevent risks like electrical fires or shocks.
In many areas, an electrical permit and final inspection are legally required.
Additionally, most sauna heater manufacturers require professional installation to maintain the product warranty. Attempting a DIY installation without a licensed electrician could not only be dangerous but might also void your insurance coverage if anything were to go wrong. Always check your local building codes before starting the project, but in almost all cases, hiring a licensed electrician is the correct and safest choice. This should be done after your framing is complete and before you install the insulation.
Lights
Now is also the time to decide how to add lights to your sauna. Traditionally, the light of the flames was considered enough, but nowadays a simple LED strip and an exterior light usually do the trick. We recommend keeping lighting low and switches outside to reduce the risk from high temperatures. LED lights should have an IP67 rating. Wiring them to be placed against the back wall gives a nice glow without being too much light.
Sauna Insulation
We spec Rockwool insulation for many reasons, including it’s fireproof, it can handle moisture, it's easy to install, and it has good R-Value per inch. It might be a little bit more expensive than other options like fiberglass, but this is one place that we’re happy to spend. Installation is pretty straightforward, just cut the bats to fit between your studs and rafters!
Tips:
Investing a small amount in a good insulation knife is totally worth it
Shop around on Facebook Marketplace, Craigslist, Offerup etc. This is one of the biggest single spends, so it can help keep your budget more manageable
Installing your sauna vapor barrier
Once the sauna is insulated, it’s time to vapor-seal the interior. This keeps moisture out of your framing, ensuring longevity (no rotting framing!). It also keeps airflow under your control with your vents, not coming in everywhere from a leaky building. Saunas use a special metal, tin foil-like, vapor barrier instead of something like housewrap, so it doesn’t melt at the high temperatures. All seams need to be taped with foil tape to ensure a continuous air barrier. Floor water and moisture proofing happens in other ways, so this only goes on the walls and ceiling.
Tips
It is very hard and frustrating to try and tape a 90-degree corner, like from the wall to the ceiling. To avoid this, overlap the vapor barrier from one to the other, taping one side in a flat section, then pushing the vapor barrier tight against the corner, then tape the other side on the flat
Before you cover up all of the framing, take pictures so you know what’s back there. You can also draw the stud layout on the floor. Once the vapor barrier is installed, you can lightly push it to see what’s back there, but marking it with a sharpie can be very helpful finding studs later on
Adding furring strips
Creating an air gap behind your interior wall cladding (your cedar tongue and groove) will help it to dry, and it keeps the wood from direct contact with the wall, where moisture could get trapped and mold or rot the wood. It’s not necessary to add furring to every stud and rafter, but they are cheap and you’ll want to make sure to have support in places like where the benches will be attached to the studs, so you might as well!
Add a furring strip to each stud and rafter, leaving a ¾” gap off the floor and ceiling to leave the air gap
It’s okay to use pine here, as it will seem minimal moisture and be hidden by the cedar cladding. If you’re concerned about the use of pine, you can rip down some of your cedar t&G into furring strips
Interior tongue and groove cladding
This is when the sauna will start to feel finished! There are a few things to pay attention to when adding the t&g, but once you get the hang of it, it’s not too hard. It pays off to work slowly and pay attention to the details — you want to be relaxing in your sauna, not looking at your construction mistakes!
We recommend a “start hard, finish easy” approach, doing the ceiling first, plus this helps with the finished look. Once you’re on to the walls, you’ll get a cleaner look by doing the front and back walls then the side walls last.
Now is also a good time to work on your window(s) and door so that you can make sure that everything lines up nicely and plays together well. We like to run the T&G straight into the door and window jambs, so they sit flush with each other and the jambs hide the ends of the T&G boards. This also lets you add an additional layer of trim if you prefer the look, or if your cut ends are messy. This means that your jambs must run 1 ½” past the studs to account for furring strips and T&G.
On the ceiling, install with the tongue side facing out, so that you can nail through the tongue
On the walls, install with the tongue facing up, starting from the bottom and working your way up, still nailing through the tongue
Use a “beater board” to get stubborn pieces together, never hammer directly on the tongue. If one end pops in and the other pops out, nail one one side, then work your way over to the other side, seating the tongue into the groove as you go
You don’t need to nail on every joist or stud, about one nail per 16-24” is sufficient
Set the depth of your nail gun to sink the nails just below the surface of the boards and nail through the tongues where possible — nails that stick out can get very hot and burn you
Galvanized nails can degrade and rust over time, staining your walls and ceiling, stainless steel nails may be one place where you want to spend some extra money
Building your sauna benches
Benches can be done in a lot of different ways, and specifics will depend on your personal design. In our 6x8’ sauna, we sought to maximize and prioritize the top bench. This means full width for laying down, but it also means the lower bench is more narrow. Materials can also make a difference in design, especially the bench tops. We’ve laid things out using 5/4 x 4 cedar deck boards for availability and pricing, designing for full-width board and no rip cuts. The support structure for the benches is made up of cedar 2x4s fastened all the way through the T&G and furring strips into the studs and blocking with 5” structural screws. The front board and middle supports get fastened together using exterior-rated pocket hole screws. This means that no fasteners are exposed, so you won’t burn yourself on the hot metal.
Cut all of your boards to length
Fasten the back and side “ledger” boards to the walls with the long structural screws that will reach all the way to the studs
Drill the pocket holes in your intermediate supports and front board, both for connecting the framing elements together and for connecting the deck boards to the supports — you definitely don’t want any exposed fasteners on the bench top, so they’ll be fastened from the bottom
Connect the support “joists” and front board with the pocket hole screws
Install the deck boards using the pre-drilled pocket holes
Sauna ventilation
This one is a heated topic, no pun intended. Proper ventilation achieves a few different things, including supplying fresh air (keeping your sauna from being stuffy), and the correct flow of heat, air, and löyly. With proper ventilation, you will reduce the high-low temperature gradient and make sure that you have fresh air to breathe. The type of heater (electric vs wood-fired) has a large impact on your ventilation needs, since the drafting air that a wood stove creates moves a significant volume of air compared to an electric heater. Our considerations here are for electric stoves.
Mechanical vs passive venting for a sauna with an electrical heater
The best way to achieve proper airflow and ventilation in your sauna is with mechanical venting — using an electric fan to move air. That said, it’s possible to achieve some good outcomes with passive venting. According to the sauna bible (Trumpkin’s Sauna Notes), mechanical ventilation is essential to proper airflow and even for things like exhausting CO2.
Mechanical ventilation setup
A “Mechanical Downdraft” ventilation is the preferred method for electric heater - simplified, this means an adjustable (non-mechanical) vent just above the heater, and a mechanical (electrical) exhaust vent below the lower bench.
The mechanical part of the vent will be an inline vent fan that can operate at around 100 CFM. Operating well below max helps with the noise, or you can add a silencer, and use straps rather than fixing the duct directly tot he structure to reduce vibrations
Vents should both be 4” round with solid (not flex) duct, snap lock duct is easier to work with; cut it before you snap it together!
Here’s an example of a fan that is recommended
The fan is mounted in the duct and will need to be wired in by your electrician
Do keep in mind, this vent setup will likely be longer than your wall is thick, meaning it will protrude from the exterior wall. You’ll need to frame out a small box to house this. Here’s an example of how one r/sauna user did the build.
Lastly, a secondary passive supply may be needed to cool the heater and its heat sensors — adding more fresh air might actually help your sauna get hotter! Investigate this option if your heater keeps turning off due to hitting its limits.
Passive ventilation
Using a couple of vents with adjustable flow (via sliding covers) will let you find the best balance of temperature control and fresh air without the complication and cost of mechanical ventilation. This might not satisfy the purists who demand perfection in airflow, but it’s your sauna. We’d recommend three vents total, 1) below the heater 2) opposite the heater under the lower bench and 3) across from the heater high up near the ceiling. Tuning these vents will help control airflow.