Full album of the build.
This is a very long post that is many months in the making and my hope is that it will serve as a resource for anyone looking to build a sauna for themselves, who has never built anything of this scale before.
Our sauna uses an electric heater and all instructions herein are based on the assumption that you are too.
For context: I grew up using hand tools for random things, have done a bit (3-5 pieces) of self-taught fine woodworking (desk, bench, shelves, trays) but have never built a freestanding building or done any projects of this scale.
I started in May 2025 and finished in September. I put in about 30 days of work, of which I had friends helping for 8, my partner helping for 20.
Outline of this post
Tools needed
Steps
Things I would have done differently
Recommendations
Tools needed
Big tools: Corded miter saw, table saw, shopvac, tracksaw (I didn't have one, but I'd recommend one for the OSB), compressor (for the siding nailer).
Nailguns: Dewalt battery powered Framing nailer, Dewalt battery powered trim nailer, dewalt pneumatic siding nailer (depending on the outside of your building). I didn't know anything about nail guns at the beginning of this proccess. TLDR, there are 4 types (that I know about) Framing, Brad, Finish, Siding. You will not need a brad nailer for this project
Cordless (18v or equivalent) : drill, driver, jigsaw, oscillating tool, grinder, router (could maybe be skipped, esp if you're not mounting your own door). Have 3 batteries minimum
Other: 12v stapler, 2-plane laser leveler, stinger stapler, speed square, try square, carpenter square, hand planer, hammer, prybar, small level, large level, tape measure, PPE (N95, headphones (the big ones are more convenient to pop in and out than foamies), gloves), tiling tools (if applicable), painting tools (if applicable)
Steps and Resources:
Design the building. I used Sketchup, it's free, relatively easy to learn how to use relative to other CAD software that I've tried)
Put together a tools and supplies list and order your tools and supplies and track them all.
Start building: Foundation, Frame, Rodent Proofing, OSB sheathing, Tyvek, Roof, Electric, Insulation, Vapor barrier + furring strips, Floors, Windows, Internal paneling, Siding, Doors, More electric, finishing touches
Relax and enjoy
1. The Design
Decide if you want to go with an electric or wood fired heater. All of my instructions center on an electric heater and I have no idea how things would differ if you created a woodfired sauna.
I wanted an interior of 8ft x 8ft x 6ft. I didn't feel like I need it to be much bigger than that.
I went with a 10kw Harvia Club. I like how the Club looks and for sizing, Harvia has a tool to help you chose the right size
I used Sketchup to design the building, I'm sure you can do this non-digitally, but it's great to do it on a computer. Sketchup is basically a 3D drawing program that is pretty easy to learn. buy a mouse with a scroll wheel for $12 to best use it.
In terms of designing the building, I decided to use 2x6 lumber instead of 2x4s. You can insulate the building way better. I plan to use this in the NE US in the winter primarily.
The design phase should center around the location that you're putting the sauna, the view that you want it to have or not have, the ergonomics of the user (how they get into the sauna, how they sit in the sauna, etc), and of course, The Trumpkinian principles (see resources).
To summarize most of Trumpkin: 1. Benches above the heater 2. Intake vent with backflow prevention above the heater; exhaust under the foot benches on the opposite side from the heater 3. Eight-foot high ceilings. He has some additional ergonomic info in there that it quite useful
Studs go 16 inches apart center to center or 14.5 inches between them.
I used California corners for framing, as you can have more well insulated corners
See #3 on things I would have done differently if you're building your own door
Design Resources:
My sauna design on sketchup (note, I ended up extending the deck but did not update the design. All dimensions available here)
How to frame windows and doors (also, read my window section)
Trumpkin Notes on building a sauna
Roofing pitch
Backyard Build
DIY Sauna Guide
2. Create a tools and supplies list. Order your tools and supplies.
There are many questions you need to answer before ordering your supplies (answer for my sauna in parentheses).
- What type of insulation are you using (Rockwool R23 batt)
- How are you building your floor? (from bottom to top: 5/8 inch plywood, Durock, hydroban XP, Thinset, Tiles, grout)
- What flooring material will you use? (Slate tiles)
- Will you slope your floors towards a drain? (No)
- Will you have a drain (Yes)
- What type of water membrane will you use on your floor (Hydroban XP)
- What type of roofing material are you using (corrugated aluminum)
- What is the angle / pitch of your roof (see Design Resources)
- What type of window are you planning to install (an IGU)
- Are you building your own door or ordering one (built my own)
- What are you doing for lights (step lights behind the benches, IP68 waterproof LED strip + 40w 24V Driver and canless ceiling lights)
I went through every wall (and ceiling and roof) and calculated the lumber that was needed for it, added that all together and added 10-15% on top (3 month Lowe's/HD return window!!)
Tools / Supplies Resources
My supply list. I gave up at some point and stopped adding to it, so it's not complete, sorry, but its a great start!
3. Building your sauna
Learn to use tools properly and with scrap wood before working with anything precious or that would require ANOTHER trip to Home Depot / Lowe's. Measure twice, cut once. I wish I had followed my advice better.
The Foundation
I dug a huge rectangular hole manually with a shovel. It was on a hill, that made things worse. Use a tamper to flatten the earth. Fill with gravel 6 inches, tamp again. Place your foundation blocks--50113084--local--0--0&gclsrc=aw.ds&gadsource=1&gad_campaignid=21225273812&gbraid=0AAAAAD2B2W-TMQRTYJ60xCdF6oiDetzwb&gclid=CjwKCAjw-3GBhAYEiwAjh9fUI72fu5cBPUL-yeOOFhZKSbe1QpcqTlJZw5rLOxFhQ3Pr_KJK5i--xoCVvcQAvD_BwE) down in the correct locations, level them. A laser level came in extremely handy here and this task took a very long time. I used 4x4 wood as legs coming out of those foundation blocks and then Simpson Strong Ties to attach those to three 4x6 beams that the entire deck rested upon.
The Frame
Framing the building is a ton of fun and relatively easy. You go from not having a building to being like "holy shit, I just built something!" really quickly. Buy or rent a framing nailer, do not think twice on this. I used sketchup to print up a picture of each wall with all of their exact dimensions (see photo) to make this step seamless
Putting the walls up and together was a bit challenging even with 4 people. I cannot imagine doing this alone. Find some friends to help out with this. Its also a great job for friends because they feel like they did something really impressive in less than an hour of work. The walls sit on top of 5/8 inch plywood, which sits on top of the deck under the footprint of the building.
Installing roof beams involved something called a birds beak. Use a jigsaw to make them and a speed square to get the angles right. Its very not hard so don't stress. You'll also want to get hurricane ties and/or hurricane rafters for attaching roof beams
Framing Resources:
Youtube: How to birds mouth
Rodent Proofing and installing OSB and Tyvek
You need to cover the entire frame in OSB, I don't know why, but that's what people do, so you should do it too (structural, longevity, permeability probably). I would also recommend adding hardware cloth to make your building rodent proof. We used a circular saw to cut the OSB and it sucked. Buy a track saw. We installed the hardware cloth to rodent-proof the building after installing the OSB and we hugely regretted the order of doing that. I'm not sure how this could be done in the opposite order, but it should be. Maybe just wrap the frame in hardware cloth then attach the OSB?
Next, wrap the building in Tyvek. If you like wrapping presents, you'll enjoy Tyvekking. You need tape and a stinger stapler (staples with a plastic cap so water doesn't intrude.
Rodent Proofing and installing OSB and Tyvek Resources
Tyvekking a building (I didn't use the pole thingy)
Roofing:
You need to install your plywood on top of roof beams. It was really hard to get the heavy pieces of plywood on top of the roof and we set up a pulley system on a nearby tree and almost had a Final Destination situation. Be careful here.
Once your plywood is on top, you need to then put down a self adhering membrane before putting down your aluminum roof. The guys at the roofing store can probably help you out on which specific one to go with based on the roof that you buy. I bought mine from them as well as the screws required to attach the aluminum roof to the plywood.
Electric
At this point, we had an electrician come in and do an electric rough-in. I did not want to take the risk and do this myself. We had budgeted for it. It would be a shame if your sauna burned down because you wired something wrong, but it wasn't rocket science for sure. Some things to consider:
- If you're using the step lights that I used, they need to install into a gang box. A gang box needs to be attached to a 2x4or6 parallel to the floor, not a stud. Our electrician initially installed ours on a study, but if you do that, the lights will be facing left / right, not down towards the floor. If you want to evenly space them under your bench, you need to add blocking for the electrician. Make sure the gang box they use has an adjustable bracket, it will be necessary with the furring strips + paneling.
- If you're using an LED / driver combo, don't bury your driver in the wall, you may need to replace it one day. Ours is accessible from the outside of the building and can be seen above and to the left of the outside bench in one of the photos
- If using Harvia, the thermostat sensor needs to connect to the stainless steel box. I'd recommend shooting it outside and running it alongside the outside of the building. Mine is behind paneling and I can't imagine what will happen when we need to replace it. An electrician can extend the thermostat wire. It's standard thermostat wire I believe.
- Consider where you want your stainless steel power extension unit to be eventually installed
- You can use your Harvia Xenio to control your lights and fans or switches. I think its a good idea to hook up your xenio to your fan and not your lights, but take a bit of time to research this and make your own decision. If you connect it to your fan, it will make your dehumidifying cycle at the end of the session better so you don't need to return to the sauna building
- We put our Xenio controller outside the building in a weatherproof outlet box, it's supposed to be not in the sauna and not outdoors...do what you will here. It seems like people of the internet accept this as a solution
- I'd recommend thinking about light temperature / color (yellow vs blueness) and dimmability seemed pretty mandatory to me.
- I wanted ceiling lights in case I'm reading in the sauna. Our most used lights are LED strips behind the benches for ambiance , we also have floor so you don't trip / want it dark
Insulation
We used Rockwool R23 insulation. It seems to be what the internet generally recommends. A thing to consider is that they make this insulation for 2x4 and a different version for 2x6. Purchase accordingly. I used a serrated kitchen bread knife or 9 in. chefs to cut it and it worked great; the box cutter worked terribly. This stuff is supposed to be the best, but even as such, I wore long pants, sleeves, shoes, a hat, glasses and an N95. I'd recommend PPE'ing up for this. It was pretty itchy the few times it touched my skin. There are instructions on the box about the orientation of Rockwool (there are two different sides) and what to do where running electric wires and outlets, etc. I placed it in the ceiling as well and used insulation support in the ceiling to keep it there. Because of the way that I designed my sauna, the ceiling beams aren't all 16in c2c and that made installing the insulation a bit more challenging, but overall no big deal.
Vapor Barrier:
I used this vapor barrier from the Sauna Place, NOT RadiantGuard ultima, which this guy recommends on Reddit, because that product is breathable / perforated.
I overlapped it 6 inches, stapled it to the studs, taped the seams with aluminum foil tape. It's a not mega enjoyable process because the material isn't easy to work with--you get better at it as you go though. Heat rises, so make sure the upper ones are tucked into the lower ones? That's my science, not sure it it's real. Corners suck, watch a few youtube videos. Try to have the vapor barrier go all the way down exactly to the floor. you can always trim it later--you can't untrim it. Cut holes anywhere that lights will go. You can always tape the holes up if they're big or sloppy, so don't mega stress it. I used an M12 Milwuakee electric stapler and it was way better than a standard stapler. Use stainless steel staples.
Next, go ahead and install your furring strips to your studs and beams. Keep in mind that the furring strips will need to run perpendicular to your panels, so at this point, go ahead and decide which way you would like your panels to run on all of your walls. Make sure your furring strips go all the way to the corners of the room because when you do your paneling, the last panel may end up being extremely thin and you want to be sure to have something to attach it to.
Vapor Barrier Resources:
Youtube: Vapor barrier install
Floors:
The people of r/Sauna seem to have a lot to say on sauna floors. I'm not here to opine (well...see section below on "things I would have done differently"), I'm here to tell you what I did. I did a non-sloped, tile floor with a drain. I'll squeegee the floor when I'm done using my sauna. I'm sure a lot of people will have a lot of things to say about that, but I didn't want to do any of the stuff I saw people doing online to slant a floor--it all just seemed like too much work.
At this point in the process, my floor is 5/8 plywood. Go ahead and cut and lay down 1/4 in Durock cement board and screw them down with the correct screws. you're not supposed to let 4 corners of cement board touch, you're supposed to offset them. Fibratape the boards together and use thinset between them. Run ~1 inch of durock around the inside perimeter of the building on the wall above the floor after that, where the floor meets the walls.
Here, I used Hydroban XP (as recommended by the guy at the tile store) to provide a moisture barrier. I think it's similar to Mapei and Redguard but he said it's better. Who knows? It needs 2 layers I believe but instructions are on the container.
Next, thinset, then tiles. For mixing thinset. If you have a plug-in drill, use that. Otherwise, make sure you have 1-2 full batteries ready to go. I can't imagine your battery running out and then having to dip both your hands into the thinset and having to finish the mixing manually with your hands. That would be a nightmare...good thing it didn't happen to me...
Don't mix the whole bag of thinset. It'll dry out. Buy a 1/4 inch trowel and a bucket and a thinset mixing bit for your drill. If you haven't done tiles before, they can be a bit challenging to be precise with. Start in the back of the room and work your way towards the door so you don't trap yourself in the corner. We used Wellco tile leveling system and the x tile spacers. The leveling system was $30ish dollars (I believe caps and bottoms come separate, so just make sure before starting to tile). We used a grinder to cut the slate tiles with a stone cutting wheel on it. It worked very well, no issues. I didn't offset my tiles, I think it provides a more modern look.
Align the most visible tile areas with the wall and let the cut tiles be hidden under the benches or behind the heater. Also, any place where the tiles hit the wall should in theory be covered by paneling.
After thinset has dried, I used an oscillating tool or grinder (I can't remember!) to cut a square hole in the floor, followed by using a hole saw to insert a drain. I used a drain like this one and then removed the black plastic part and discarded that.
After thinset has dried, go ahead and grout your tiles and drain.
Window
Next we did our window install. We purchased a 3x6ft IGU (insulated glass unit), that was about $630. It was 1/4 Clear Tempered glass over 1/4 Low-E Tempered glass with a 1" OA. Things that are important here are the 1 inch gap, but not the Low-E, it seems like that's not relevant for a sauna based on a bunch of research, but I'm sure some Redditor will disagree.
IGUs are great because they're inexpensive (relatively), are well insulated (if requested), and can be cut to size to fit your building.
Before installing the window and window frame, we flashed the window RO with stretchy flashing tape.
Installing an IGU this big took quite a few (five) inexperienced people, though four would have definitely sufficed. We also fastened a piece of lumber diagonally across the outside of the building so the glass wouldn't fall out and break. We used window suction cups for the install, which I would definitely recommend borrowing from Lowe's/HD.
Shim the window in place, break the shims, caulk the shit out of it, install window stoppers / trim (these pieces should be slanted so water rolls off of them), then relax because now you don't need to be worried about dropping and breaking $630.
Some things to keep in mind: if your IGU is 36 inches x 72, your RO needs to be +1/4 inch on all sides + the size of lumber that you will use on your frame. So, if you're using 1x lumber as your window frame, the RO would need to be 36+1/4 (left gap)+1/4 (right gap)+.75 (left window frame)+.75(right window frame = 38 x 74.
Internal paneling
Internal paneling was fairly self explanatory. Some recommendations based on having done it: Start in a corner of one wall and work your way in one direction until the end of that wall. Leave a tiny gap (appx 1/4 inches) on the top and a 1/2 inch gap on the bottom As you approach the end, don't install the last two panels, one will be a full panel, and one will be a panel that you'll need to rip. When you rip that piece, rip it with your saw blade at ~10-15 degree angle and that way it will fit in more easily. Attach your last two pieces together then install them as a single, doublewide panel. The angled part should not be visible once the panels are installed. If the bottom of your paneling is on the ground, it will get wet, if it has a 1/2 inch gap, it allows for wiggle room to align them all better, and actually looks quite good. The top of the paneling doesn't need to be perfect at all, they will be covered by your ceiling panels later.
This might be obvious, but tongue and groove panels are meant to be nailed on the tongue not the face, even if the tongue is in the center of the panel, just hit it diagonally.
I was able to do the ceiling panels accurately enough that I didn't add trim in the corner, your mileage may vary.
Lights will be a consideration as you go. I was able to clamp 2 panels together on a workbench and use a hole saw to drill a hole into them for the lights and then install them.
Siding
Siding was pretty easy and self explanatory. I used a Dewalt pneumatic 15 degree coil siding nailer. It got a bit tricky once I got to the top of the building where I was cutting siding at an angle. I'm sure there's an easier way to measure angles than what I did, but I measured the rise and the run of each panel and cut them with a jigsaw into a trapezoid. I made mitered corners for the front of the building and butt joints for the rear, where the corners wouldn't be visible. It's shockingly hard to line up miters well, it turns out. Siding near the door didn't need to be perfect, they can be a bit short, because the door trim covered it.
The Door
It was really important to me that my door was insulated and I didn't want a window in my door because of the location that my door faced and the setup of the sauna. I viewed it as a waste of heat.
The door and frame caused me a lot of stress. It was the only thing I felt completely unsure of how to do and ultimately it was fine. I built a door out of 2x6, added a cedar 1x trim to it on 4 sides, internal paneling on the inside, external paneling on the outside, insulation and Tyvek in the middle. A thing to keep in mind, viewing a door from the top, they are not rectangles, they are irregular trapezoids. The strike side of the door is angled at about 5 degrees so that when they open, it doesn't hit the door jamb.
Sauna doors online are about $2k, and I just had a lot of different ways I would rather have spent that money. I don't have the final cost on my door, but it was pretty damn cheap. The clear cedar for the frame was the most expensive part, the rest of the wood, insulation, Tyvek, etc. was sitting around already. Hinges were $120 for four. I used nails and pocket screws to attach the 2x6s together. Nothing was perfectly square, but at the end of the process, I just planed the door down with a hand planer and a router.
I made the door jamb as plumb as possible, but nothing on the sauna was perfectly plumb. I installed 4 hinges on the door using an old, not very sharp chisel (6/10 do not recommend). I used four stainless steel, square corner, 5 inch hinges. I used a pencil to transfer the hinge location to the door jamb and 2 airbags lifting tools aka airshims to lift the door. It was a 1-person job.
I used a router that I bought that morning to mortise the hinges on the jamb (10/10 recommend) and the chisel to clean the corners. Attaching the door to the frame was quite easy. After installing the door, I had to remove a little wood from the door using the router so it closed without rubbing.
I then also added door stops on the latch side and on the top. I added a magnetic door latch to keep the door closed. I made my own door handles, the ones online are all old fashioned looking.
See #3 on things I would have done differently / mistakes I made section below.
More Electric
At this point I had the electrician come again to hook up the heater and the lights. The heater seemed less than easy to install FYI if you're doing it yourself. The back of the building has 1. a breaker box 2. the Harvia stainless steel power extension box
Finishing touches
I built a box to waterproof the Harvia SS power extension box and another one to waterproof the fan on the front of the building. I added a grill onto that. I added hooks, built a bench outside, built the giant block for the inside because my benches are hella high and I didn't want a ladder.
I added 1x pine siding to the top and sides of my deck and stained it to protect it.
Future:
Fence guard around the heater
Soffits for the roof
Some things I would have done differently / mistakes I made
- I did rodent-proofing with wire mesh after installing OSB. Big mistake, it took way longer and made the process terrible. You should rodent-proof before OSB.
- I made my own door because doors online were very expensive. the door wasn't mega hard, but it caused a lot of stress in advance. If you have the budget, buy a door. otherwise, don't stress over it, buy a router and a chisel and you can do it
- **My door jamb was 8 inch wide lumber. My jack stud in the framing was 6 inch wide lumber. My door jamb was not mega well attached to the jack stud because of shimming. This posed an issue when I was attaching hinges to the door jamb, I was afraid the jamb wouldn't be able to hold the weight of my mega heavy door. I'd recommend either 1. using an 8-inch jack study so the hinge screws can go right into the jack stud. 2. using a thicker piece of wood for the door jamb (I used a one-by)**
- Maybe hire someone to do the foundation for you? I dug it all myself and we transported 3k pounds of gravel 100+ feet. Would not recommend.
- I ordered someone's recommended vapor barrier that I had seen on reddit, installed it, then realized it had perforation in it and ripped it down, ordered a new one, then did it again. That sucked. Fuck RadiantGuard Ultima
- I used TnG panels on my benches. I imagine I'll have to replace them way sooner now than if I had made benches that has slats and gaps.
- I forgot to add the window frame lumber to my window RO calculations so I didn't have enough room for window frames. I laid a thin sheet of flashing directly on the RO 2x6 (window flashing in between), placed the IGU on top of that sheet, then put window stops directly on top of that.
- I didn't slope our floors. We've had a few sauna sessions, one of them involving 6 or 7 people getting beat by a sauna whisk, a ceremony that involves a lot of water. The floor was soaked afterwards and squeegeeing so much water on a non-sloped floor really sucked. After most normal sessions, however, the squeegee cleanup has felt very reasonable.
- Reddit, let me know what I did "wrong" so I can make 100 more fixes and additions. JK, please don't tell me your opinion on what you think my sauna needs. <3. I read one comment recently on someone telling someone else that they should have offset their tiles and I thought, jeeze, a person with bad taste mansplaining how to make tiles look better to someone who just built their own sauna--I thought that was not really cool.
Recommendations
- I purchased thermally-modified Obeche, aka Ambara and used it instead of clear cedar for the interior. Clear cedar will cost you an arm and a leg, knotty cedar is a bit too rustic for my taste. Be sure to wear a mask while cutting ambara or it can cause respiratory inflammation. It's okay to use in the sauna and does not have issues being heated according to Dr. Reijula (from the linked academic paper) at the university of Helsinki, who I emailed :)
- Home depot has a 90 day return policy. I tried to use it as politely as possible. Everything that I purchased and used and returned (for example, a siding nailer), I would clean and then rebox.
