Should you insulate the floor?
You don’t have to insulate your sauna building floor, but why not do it?
With a new sauna build, I would insulate the subfloor with 2” rigid foam ripped on a table saw to widths to fit between your floor joists flush up to your subfloor. The rigid foam can rest between the floor joist cavities via 2×2 or 1×2 strips screwed into your joists 2” down from the top. Rigid foam has an R-5 value per inch. R10 in the floor is adequate.
This is the stage at which one would install sleepers on the insides of floor joists and lay down rigid foam:
8’x12′ framing with 2×6 greenI’m not a fan of batting in floors. Rodents. And if there’s a leak, which will happen if someone tips over a 5 gallon bucket of water, batting becomes a soggy wet sponge and loses its integrity. That said, our cabin has R19 between the floor joists and all has been fine for 23 years and counting.
Decking
Let us also keep in mind that many saunas, especially old school saunas, are built with cedar decking as the flooring. Sitting on the sauna bench, one can look down between the pencil spacing between 2×6″ or 5/4″ round cedar decking and see the ground beneath. I have taken many a sauna in these saunas. The heat is perfectly adequate. Fresh air works its way up between the decking, providing the necessary oxygen to fuel our wood burning sauna stoves. The sauna stove sits on pavers atop the decking. This is a simple system. Sure our feet can get cold, especially in winter, but our feet are not on the floor while we sauna.
Cedar decking is sometimes used as the floor for a sauna hot roomThose that are bent on a philosophy of “let it breathe” may be apt to build their saunas with the deck floor open to the air below option.
Our changing room floor: our feet get cold first
Cooling down in the changing room between sauna rounds, our wet feet can easily become icicles when winter cold air comes waifing into our sauna building. A cold floor against our wet feet chills our feet fast, much like trying to wash our cars with a wet rag in freezing weather. This is when , instead of a pair of Crocs or sandals, we wish we had a pair of SaunaShoes, with a thermal mass of PCM (phase change material) that radiates warmth to keep our feet warm between sauna rounds.
We build our saunas once
An insulated barrier within our sauna building subfloor is not expensive. My $100,000 sauna plan details a radiant heat system within the floor, using tubing created by Uponor, the Finnish radiant heat company. This system is a nod toward the thermal properties of a heat mass radiating heat deep into our feet. (more on thermal heat here). This system is a nod towards “ahhhh that feels nice” when it’s a bitter cold, star filled sub zero night outside, as we return to our changing room and feel warmth on our feet, crack a cold beverage, and enjoy casual conversation with our sauna guests, barely making out their foggy faces across the room engulfed in waves of misty cool steam. Breathe in this moist cool air. Stand and stretch. Our bodies become rejuvenated as our minds open up to fresh ideas, thoughts, as antithesis of the Forgotten Sanctity of Sauna.
The authentic sauna experience is more than just the hot room
A warm changing room floor allows our feet to stay warm longer. This allows us to enjoy a longer winter cool down session. Why is this significant? A longer cool down session brings our body temperature back to normal before we go back into the hot room. With our bodies completely cooled, we are able to enjoy a longer, more fulfilling hot room session. More: Rubber Band Theory. The alternative is that, with cold feet, we rush ourselves back into the hot room to warm up, but we are less aware that our bodies are still too warm from the previous round.
Simply stated, Jackrabbing our sauna rounds limits the enjoyment and fulfillment of the authentic sauna experience. An insulated subfloor is not critical, but sure feels nice on a cold winter’s night.
20 thoughts on “Let’s review options for our new sauna hot room and changing room floor”
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Our Sauna is on a painted concrete floor. Works great, is easy to keep clean. Sauna is warm enough to keep floor comfy. With winter coming, getting ready to roll in the northwoods snow.😊⛄⛄⛄
Our sauna is built on a bed of gravel with cedar decking over the gravel. The floor is cool but never uncomfortable. The people who prefer sitting on the lower benches actually like the coolness emanating from the floor. The little bit of water splashed on the rocks for loyly is never an issue with the 10 inches of gravel. The duck board floor is made of easily removable sections for easy cleaning.
Concrete floor with duck boards in sauna. Vinyl flooring over concrete in change room. Wearing rubber sandles almost eliminates any cold feet. Used outside as well during winter to stop possible frost bite on bottom of feet while taking in the cooling freshness of the season… Northern Ontario, Canada.
Our 8×8 sauna within a 12×20 bldg has sauna floor made of 16″ of limestone 1″ gravel covered by 4^ river rock pea gravel covered with large flat stones. By the time the sauna is hot, the floor is slightly warm. Woodstove has it’s own fresh air pipe and other fresh air comes through 1/2″ gap at bottom of food. Two years of use and it still smells fresh in there, in part maybe because I often run 10 gallons of water to rinse after sauna. Perferated tile drain over plastic membrane is under the gravel.
Good ideas all around! Dropped my donation in the other day. Anxious to get started on my first sauna. When you get time wanna send me the ebook? Thanks from up here in
Grand Rapids, MN
I’m building a backyard sauna in Minneapolis (48th and Emerson Av S), and I used 2x T&G for the decking. I’m wrestling with flooring options and leaning toward glued down cork. Cork looks cool, is antimicrobial, hypoallergenic, and good insulator. My plan would be to put down smooth 1/2” plywood over the decking and glue the cork tiles to that. What do folks think of this idea given the temperature extremes?
Bill. We are talking about your floor here. Right now you’ve got 1 1/2″ thick tongue and groove floor boards, yes? Is this pine? Glue down cork is uncharted waters for me, but open to your thinking. You talking hot room, x room or ?
First thing is that hot room floor doesn’t get that hot. I’ve had plenty of 56th and Dupont Ave. S saunas where a cold beverage stays pretty cool on the floor of the hot room.
Glenn – yes, I used T&G pine for decking instead of plywood…trying to avoid anything with glue, etc. My plan was to level that out either with one of those self-leveling compounds or just put 1/2″ plywood down so that I’d have a nice smooth surface to glue the cork tile too. I’m thinking of doing this in both hot room and changing room. I agree on the floor not getting too hot, so I guess the question really is whether the extreme cold is likely to cause problems?
I sent this question to one of the cork manufacturers too, but haven’t gotten a reply. You should swing by and check it out. I’m going electric (I know, I know, but I’ve got wood burner at my cabin and wanted optimal convenience) and that’s in, so just finishing up insulation and then getting going on the interior. If you drive up 48th from the Parkway you’ll see the bright blue sauna in the backyard.
Just at the point of collecting materials to build my first sauna on the Magnetawan River in Ontario!
Prob have a lot of questions coming here and there but have bought your e-book!
Wonder about the hot room floor. Have you ever seen the Schluter System used? Usually used in showers, just wondering if it could work in the hot room? Ive heard you mention the floor is actually nice and cool.
My plan is to build on top of an old Galvanized dock frame that i’ll level on top gravel with some cottage pads. The frame is 5’5” x 12’ and I’m thinking of just putting decking directly on it and then subfloor followed by the schluter stuff with drains.
But like most people here I have nover done something like this!
Thanks!
Hi John:
You can do this, and i’m sure it’ll turn out just fine. Keep in mind, on the other end of the spectrum, you can stop at the floor decking stage. I have taken plenty of saunas, lake side saunas mainly, where you can see through the deck cracks to the ground underneath. Great ventilation, great drainage, simple cost effective flooring solution for a good sauna hot room. Please listen to Sauna Talk episode with Dave and Judy Pearson where we talk more about their awesome sauna built this way (along with discussing some beautiful spiritual elements to sauna).
I’ve read that a cooler floor insures proper air circulation and venting. Sauna heaters are designed fo taken advantage of this condition.
That doesn’t mean removable cedar grated floor panels can’t be used. The panels can be lifted out routinely to disinfect the concrete floor. This is a very common setup for flooring behind a commercial bar.
Hi Joe: A cooler floor may help circulation, but in places like Minnesota and Alaska it’s a cement floor is an iceberg in Winter time, and the A job is to isolate the iceberg. Yes, cedar floor over concrete is much better on the feet. Appreciate the feedback.
Glenn, I purchased the e-book 12-24 months ago….can’t remember when. New computer now. How do I log in and get access to the ebook again?
Thanks, Tom
Tom,
Resending you the ebook. You can print the pdf, and you’re off to the races! Happy for your sauna build.
Im building a small 6’x6′ on deck blocks 6″ above ground. I layed 6m water barrier on the ground. I’ve framed the floor with treated 2×6 and insulated with rigged foam between joists level to subfloor. The subfloor is untreated plywood. I had a spare sheet of treated plywood I’ve used as a sheathing to prevent rodents and act as another vapour barrier. I placed it under the joists. After reading up on ventilation I’m curious if this treated plywood underneath will be an issue?
*To note that the treated plywood is at the bottom of 2×6 with 2″ gap then 4″ of rigid foam then the untreated plywood floor.
Justin: Appreciate your sentiment about green treated and sauna. I see no issue here. Matter of fact, I go with treated plywood as the subfloor. Then, as you know, it’s “ben square” or bicycle spoke sleepers, cement board, skim, coat over that. I even use green 2x for drip edge.
But all this green material gets buried by other material, and it’s relatively very cool down there.
Sauna on Justin!
Hey Glenn,
I’m building a sauna in the backyard and weighing my flooring options. I’ve got a bunch of 2×4 cedar decking so I’m thinking of just laying that down for the floor. Do you recommend the foam insulation under the hot room floor if I’m going with decking? Will that still alow for airflow and drainage? Appreciate your input and all the information. Going to look into getting the e book.
-Vince
Hi Vince,
Yes, if you are working with an empty canvas (ie new build) then I would side step the idea of building a sauna atop a deck and go with building the same framework (2×6 green) then rigid between the floor joists, then a subfloor, then the Ben Square, Trevor Trowel, drain and off to the races.
All this is detailed in the e-book, and you’ll benefit from that.
Hi there, Im reaching out from northern Ontario. Im planning my build for the spring. Im torn with what way to go for my 12×8 floor. I have purhcased your ebook and like your method with the Ben square method as well as the vynyl cement on top of the cement board. Question regrarding this. #1) Have you ever had it crack on you wich allowed water and moisture to get under the cement boards and rot the floor?
Hi JF.
No, the cement board skim coating has never cracked on me.
But if it does crack on you, you can come back and mix some vinyl cement and skim coat on top of it, resealing. I like this material. It is forgiving. There are other options, as we know. (Redguard, slab pour, tiling, etc.) As most of the time we lay down duck board or raised floor atop, this system has worked well.