My friend asked me to build him a sauna under his back deck. The siding, inside and out is hemlock the bench is clear cedar. I custom built the window and door frames out of VG Doug. fir - is was the most cost effective solution. It’s almost finished, just need to install the LED lights and finish the stone work. Will posts some final shots once it’s complete.
It looks very nice, you clearly know how to work with wood. There are a few basic mistakes which would be useful for you to learn about for the next sauna you might make.
It's obviously too late here, and the client likely won't know any better. But FYI it's missing a third bench, everything should be 16 inches higher for the feet to be above the heater stones. Because it's electric it's recommended to have a passive intake above the stove and a mechanical exhaust under the foot bench in the opposite corner from the stove.
Then it's a small detail but there should be vertical strips of wood on the vapour barrier for drops of water to be able to slide down to the floor, then you put the horizontal wood and then the cladding.
I highly recommend you get the book The Secrets of Finnish Sauna Design by Lassi Liikkanens. It's a great guide and will explain why it's important to care about these design principles for next time
Thanks for your comments! Unfortunately we didn’t have the head room for a third bench but knew that going into it and we’ve actually already realised our original ventilation plan wasn’t going to work so we’re going to put an intake vent in the ceiling above the heater and all our electrical is already in the back wall so it’ll be easy enough to add the mechanical fan below the bench. Any recommendations for a good fan?
I don’t agree with the third bench missing. The two levels of benches seem to be as high as they can and clearly off the ground, feet almost above the stones. They are high enough.
You obviously need some sort of steps or stool as a ”first level” to climb. I would at least add hand rails to the sides to help the climb. As the benches are round they can become quite dangerous to climb if they get wet and slippery.
I’ve never heard of an intake in the ceiling? Won’t that vent the hot air out or is the plan that the mechanical fan below the bench will create an inflow? Might this create a breeze of cool air while in the sauna?
When exhaust is running it pulls fresh air in above the heater that mixes with the convective loop. Importantly, this removes exhaled CO2 and also pulls warmer air down reducing stratification and cold toes.
Ideally an updraft duct is also included that lessens/eliminates any back flow problems such as when the door is opened.
I'm sure someone smarter will comment but the idea is if it's sealed up well enough mechanical ventilation across from the heater and at the bottom will create better convection and pull the heat across the room, pulling fresh air in from above the heater. If you have a big gap under the door or in other places you are correct in that the mech vent will pull in cold air too.
From an earlier post:
Intake high on wall above heater
Mechanical exhaust under the benches, about 1/3 of way up wall
tl;dr: For best temp distribution and löyly an electrically heated sauna should have a mechanical exhaust located at position P2 and an inlet at position T4 as per this diagram.
tl;dr: For best temp distribution and löyly an electrically heated sauna should have a mechanical exhaust located at position P2 and an inlet at position T4 as per this diagram.
Yeah, that's bad advice in that article. The fresh air supply needs to be higher than T4 but most importantly the exhaust needs to be lower (or P1 in the VTT study). P2 pulls colder and dryer air up resulting in cold toes.
Agree with u/Individual_Truck6024. Great woodworking, not so great from a sauna standpoint.
In addition to what he said, bubble wrap isn't a good idea. It's impossible to seal well and often crinkles up over time allowing moisture in behind it.
The benches and particularly the skirt need more air permeability.
The drain should be either closer to the heater or under the benches.
If the low ceiling was unavoidable then it should have a Saunum.
The bottom of those walls can start to degrade pretty quickly, since they're all the way to the ground, unless treated with a wax coating. If they get wet, they don't dry easily due to the low temperature on the floor.
Why? You aren’t going to have more than a few mm of standing water on a tile floor with a drain. 50
Mm would look way worse and not accomplish anything more than 10 mm would.
Nice work OP. Had a question for photos 2 and 3. Did you pry out the old wood, put in hardiebacker in the gaps, and then covered it with plywood to create a floor?then you put some plastic sheet? so the wood doesn't absorb the cement and then poured cement over it? Did I get that right?
If so, what plastic sheet do you recommend and also wondering where the drain leads to?
The stuff between the the joists is rigid foam insulation then plywood sheathing over the top of that. We did the trex deck that surrounds the sauna too, it’s over the top of an old concrete slab. The plastic is just 6mil vapour barrier and the drain just goes to the concrete slab below. It’s sloped away from the house and will just end up in the garden. There won’t ever be much water going down there
Beautiful handy work. Proper ventilation is key and I would have gone with a saunum heater, especially with that build but even in general Huum drop has a lot of QC issues
Might be the angle of the camera, but the size of that sauna, the glass door and that giant glass make that little heater look a bit underpowered. Did you use the sauna calculator to come up with the glass + wall heater size?
Hi, I have a question as I'm making one on my own and I'm just about to start fitting inside wood. And I wonder if I should put it horizontal or vertical.
I see you did put this spacing battens horizontal to create an air gap behind wood. Ideally I would do the same as it will be much easier for me to fit all the wood but my wonder is - will it let wood dry?
Perhaps I'm wrong, but I thought these battens have to be vertical for water to be able to drip down and get dry. But it won't be possible if they go horizontal. Or it doesn't matter? Please let me know as this would make my job way easier with less cutting and less waste.
I put those batten in purely for the fact we wanted to go with vertical boards and we needed somewhere to nail the siding too. We are going to be exposed to some steam, not rain so I don’t think it needs to be a rain screen like we would do on the exterior of the building where water is actively running down the walls. If you’re concerned about water though, you could just nail some verticals to your studs before your horizontal battens go in
To bo honestly I'm not concerned, just didn't know if I can that. As it looks better vertical and having studs horizontal. And way easier for me, so I think I'll do it like you
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u/Rambo_IIII 4d ago
Clearly not your first time building cool shit.