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itsnotrequired 12-10-2013 08:27 AM

sauna flooring
i am presently building an outdoor sauna and am struggling coming up with a good flooring solution. floor is presently 3/4" treated plywood on top of a 2x6 subfloor, with joists 16" o.c. there is 2" xps foam in the joist cavities, such that it is flush with the top of the joists. the foam is friction fit with some intermediate supports in the cavities, to keep the foam from falling out for some reason. the whole subfloor sits on 6x6 timbers, which are set half in the ground. in other words, the subfloor is off the ground with free air flow underneath.

sauna building is composed of two rooms, a 'changing' or transition room which is accessed from the exterior and the hot room, which is only accessed from the transition room. hot room will have the heater and will get hot (up to 180 degree) but the transition room will only heat up via whatever residual heat makes its way into the room from the hot room.

so i am looking at two rooms and thinking two different flooring systems. in the transition room, looking at placing 1/4" or 1/2" plywood underlayment and covering with sheet vinyl. in the hot room, looking at 1/2" cement board underlayment and then tile.

thoughts? keep in mind this will be a 'dry' sauna so moisture shouldn't be a large issue. my biggest concern is the temp difference in the hot room. the ceiling may get up to 180 degree but i can't imagine the floor getting much hotter than 80 degree. still, cracking seems like a concern.


oh'mike 12-10-2013 10:00 PM

Tile and backer board will take the heat --and in a small space like that the expansion should not cause problems----

you are in uncharted waters ,however, so you may have a failure---That wouldn't stop me--it's a small room--the cost of failure is small---so I would take a chance.

itsnotrequired 12-11-2013 08:23 AM

thanks, mike. my concern is less with the maximum temperature it will be exposed to but rather the cycling between hot and cold when operated in the winter months. the room could be as cool as 20 degrees or so when i fire it up and in an hour, the floor would be near 70 degrees. that's why i was thinking vinyl might be a better choice. the rooms are indeed small, the hot room being about 7' x 6'-4" and the transition room about 7'-4" x 4'-6".

any advice on tile type, ceramic vs porcelain? some other material?

oh'mike 12-11-2013 06:27 PM

Defiantly a good quality porcelain--(those can take freezing without breaking)--set your cement backer board in thinset and nail it down--then use a good modified thinset---

JazMan 12-11-2013 09:26 PM


the whole subfloor sits on 6x6 timbers, which are set half in the ground.
You're not saying the subfloor is 3" off the ground are you? I hope the 6x6 are set vertically as posts. So, confirm how much space between floor and ground.

So it's a dry sauna and there's no water/moisture/steam involved at all?

I'm not too crazy about the subfloor/underlayment plans, but more later.


oh'mike 12-12-2013 04:50 AM

I just reread your original post---The treated ply is a problem---that moisture level in that product is to high for tile---you will need to let that ply dry out for months before you can trust it to stop moving----

Also,as Jaz pointed out--if you have 6x6 sleepers laying on the earth, you will have a damp floor structure.--not safe for tiles---

Loose laid brick? Sheet vinyl is not good as it will trap moisture that is under the floor--

itsnotrequired 12-12-2013 07:58 AM

2 Attachment(s)
here are a couple pics of what my setup is. the soil in this area is almost all sand. i removed the small amount of topsoil in the area down to sand and backfilled/compacted with clean sand i had from another project. the timbers are only set about an inch and a half in the sand, just to help hold it in place. then a 2x6 frame on top, with 2x4 'sleepers' on the tops of the timbers, to help support the 2" xps foam between joists. 3/4" treated deck on top. so the bottom of the deck is 9" or so off the ground but it isn't exposed from below, due to the foam in the joist cavities. idea of raising it was possible future portability but also to get some airflow underneath.

i put the deck on back in august so it has had a few months to dry out. this is a traditional finnish sauna so yes, it is quite dry. there is a small amount of water that is placed on the hot rocks periodically but we're talking about a half cup here and there. relative humidity levels will be on the order of 10-20%. some moisture will reach the floor in the form of sweat droplets or perhaps some wet feet from outside but that's about it.

oh'mike 12-12-2013 08:17 AM

Good----It's a small room---I say,take a chance and do it-----I don't think the risk of failure is great----

itsnotrequired 12-12-2013 08:44 AM

i found a sauna website that discussed troweling vinyl patch cement over top of the treated plywood to make a 'finished' floor. with duckboards on top, appearance really isn't important but would the cement even hold up?

and when i say 'duckboards', i'm talking about removable cedar mats that lay on the floor

itsnotrequired 12-12-2013 12:19 PM

another material i was thinking of was rubber sheeting, like the stuff used on built-up rooftops or garage floors. it would be really easy to install and if it is good enough for garages and rooftops, it should certainly hold up in a sauna. aesthetics really aren't that critical to me since i'll have duckboards down.

oh'mike 12-12-2013 07:01 PM

Just paint the subfloor well and then lay down the slats----just a thought---

alexjoe 12-13-2013 11:48 AM

Yes you are right.

juels98 10-05-2016 03:31 PM

Re: sauna flooring

I have my sauna I build done exactly as you described in your original post. It's sitting up in the air, on 6x6 posts, with 2" rigid insulation in the floor cavities. I planned on having water in the hot room, so I built up sleepers on my green subfloor and put Durock over them sloping towards the drain. I also had a shower liner on top of Durock. The point is, I couldn't decide how I wanted to finish it. In the end, my inspector mandated I make it non-combustible. So, I put cement over the hot room floor- cheap, easy, and at 1/2" thick probably less weight than tile. I'm glad I did-- it's cool to walk on because heat rises and cold air falls. It also looks nice. I have duck board sitting on top of it simply for looks.

As far as the changing room-- mine is 12x8 :) it's a social place for me. For the floor-- I simply put down a piece of sheet vinyl flooring from Menards. It looks nice and seems to work well-- again install took 30 min :).


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