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The definitive word on what kind of glass to use for windows in the sauna (I can really see clearly now)

As many know, I have built a bunch of saunas.  I help hundreds build their own sauna thanks to my ebook (and an unwavering enthusiasm to help folks build their own kick ass saunas (and with no compromises).  This question comes up frequently:

What kind of glass should I use for windows in the sauna?

Well, I finally got through with an expert in the field.  And it took a lot of work.

Folks in the glass industry seem about as temperamental as the product they sell.  Folks in the industry that I have spoken with are not patient and they do not like lots of questions.  And no wonder, ordering custom cut glass is an involved process.  There are many options to choose from and every order involves verifying dimensions.  Mistakes are costly.

But I finally have been connected to an expert in the field who was patient and friendly, and locked into my barrage of questions.  Michelle is a glass industry expert with 17 years experience.  Even better is that she told me “I never stop learning” which tells me that she is open minded enough to keep expanding her knowledge in the field.  (This, by the way, is exactly my theory of sauna building, which is why my ebook is open to involving with sauna builders’ generated content).

Ok, enough of all that, here’s the scoop:

For windows in your sauna:

  1. Plan your sauna window carefully.  I am a big fan of transom windows up high. – 16″x 30″ or so.  They don’t get in the way with whatever is underneath, and allow privacy.  There is the candle window, and window in the hot room door.
  2. Contact a local glass company.
  3. Order 1/4″ insulated tempered glass, cut 1/8″ to 1/4″ less than your rough opening.
  4. Frame in the glass using the same material as your hot room (cedar paneling ripped to size).
  5. Run a bead of silicone around the inside and outside of window.

Insulated tempered glass is two pieces of glass bonded together.  This creates an insulated unit.  This system reduces moisture on the glass.  This system helps facilitate the temperature extremes of a sauna hot room and a cold winter’s night.

What if the seal of the double pane glass breaks down and moisture gets between the glass?

This shouldn’t happen, but if it does, we are shit out of luck.  We either have to live with it or replace the glass.

What about cost?

a 16″x30″ insulated tempered 1/4″ piece of glass costs $93.00.  That’s about twice the price of single pane.  But this price is a fraction of the price of buying a window.  We build our saunas one time.  Let’s use the best glass option we can find for our sauna windows.

a hot room transom window as viewed from the outside, with saunatimes promotional material underneath.

 

 

For more discussion and clarity on windows in the sauna, please read here.

 

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22 thoughts on “The definitive word on what kind of glass to use for windows in the sauna (I can really see clearly now)”

  1. Thanks a lot for going into all the trouble getting a competent answer to this important issue!

    All the best,
    John

  2. for those not wishing to fool around with framing in a window, sauna supply companies offer complete windows. these are made from tempered glass, available in different sizes/colors (e.g. tinted but costs more than clear), different wood (cedar, aspen, etc.), beveled frames for water runoff and typical come with trim pieces. set in place, a few nails and done. this is what i did with my build. i have a clear window between the hot/changing rooms. window cost me $170 (w/o shipping) and for me, the extra cash was worth it.

  3. Good info, Glenn. I went with a vinyl slider in the hot room. One pane is currently cracked and the frame of the slider warped a bit during an especially hot session. It’s still functioning, but eventually I’ll replace it with a tempered wood frame window.

  4. I acquired a 2×2 double pane window glass. I was worried about breakage as it is just above my 6kw heater…two years now and works like a champ.

  5. My 36″x36″ sauna window developed two top-to-bottom cracks recently, after the sauna temperature reached 210 degrees. It was only about 32 degrees outside at the time. The cracks are only in the inside pane, but there is some displacement of the glass and I’m worried it might fall in if accidentally bumped. Does anyone know of any product I could put on the cracks as a temporary measure? ie. high heat silicone? I’m worried about investing in another window in case the same thing happens again 🙁

  6. i’d go with silicone for sure. And then when it comes time to replace the glass, consider breaking up the 36″x36″ window into multiple (smaller) panes so the chances of cracking will be less and if your window does crack, it’ll be a smaller piece and that much less of a pain.

  7. I’ve been seeing pictures of modern saunas with very large windows and even patio doors, is this ok ? I guess vinyl is out of the question , should they be triple pane glass ?

  8. Alain: You’re right on about the newish trend towards “big glass” windows in our saunas. Thermal pane technology is allowing for some pretty large windows. The inside of a hot room can be 200 degrees f. hotter than the outside, making for a seemingly impossible temperature extreme and tolerance for glass to be able to handle. But this is all possible thanks to the advent and invention of thermal layering, as you point out. I”m not exactly sure if triple pane is the answer. As this is an important, and fairly expensive element to your sauna, my advice is to get with a glass company, explain your application, and have them “spec” the window for your sauna. This way, they are somewhat on the hook to help ensure you get the right glass for your sauna application. Good luck, take pics! send our way.

  9. Hello,

    I just finished a 8×12 ft. outdoor sauna and took it on its maiden voyage tonight and it works great! The Only problem is my large 3×5 ft. window has developed a long crack on the upper part of the inside of the sauna and not sure why? This is what i have

    (1) piece at 60″ x 36″ converts to (1) piece at 59 3/4″ x 35 5/8″ Rough Opening dimension
    (1) piece at 60 1/4″ x 13″ converts to (1) piece at 60″ x 12 5/8″ Rough Opening dimensions
    (3) pieces at 14.5″ x 14.5″ converts to (3) pieces at 14 1/8″ x 14 1/4″ Rough Opening dimensions

    1″ OA and will include low-e

    I had an option of tempered or Annealed and this is what the glass place told me.
    “Annealed is when if something breaks the glass, it breaks into shards. Tempered is when if it breaks it will break into tiny pieces in order not to cut anyone. 🙂 We had chatted about tempered, but I believe you opted for annealed, as tempered isn’t necessarily a stronger glass.”

    Is it possible the window was flawed and they may be a leek? I believe it is warranted but want to order the correct window when replacing. BTW this is just glass i framed it in.

    Thanks for your helpful responses!

  10. Bummer Dennis! Glass cracking may be due to the heat extreme or may be due to some too tight application upon install. I’d suggest bringing up the issue to glass expert in your area. They will probably jump right on the heat issue right away, but you will point out to them that glass is used in hot environments all the time. Some sauna doors are all glass, as example.

    3×5 is quite an opening. Forgive as i didn’t quite follow with your dimensions above, but after taking out the cracked glass, you may want to consider converting that large rough opening from a 3×5 to maybe 2 @ 3×2 1/2 or something like that, thereby 2 pieces of glass vs. one large. I know it will break up the intended big window look but maybe that’s just too big of a piece of glass? Keep in touch, send a pic!

  11. I love the look of the transom window. Is that simply a piece of tempered glass pushed flush up against the exterior trim and sitting on the lower 2×4 of the window opening, and then held in place by pieces of cedar trim on the inside? (with presumably a bead of silicon inside and out).

  12. Chris: you’re right there. Tempered glass cut to fit at least 1/8″ less than your rough opening.Flush up to exterior trim, bead of silicon as you mention, and the only trick is a good measurement to rip your jam to hold the glass in place on the inside. Voila! You got it.

  13. I’ve talked with a couple of glass shops and they say there is no such thing as insulated, tempered glass a quarter of an inch thick. They say they can get laminated glass that thick but not “insulated, tempered” glass – when I requested what you noted above, they looked at me like I was nuts! So – is this quarter inch laminated safety glass? Thanks!

  14. laminated is probably the same and should work great. As long as our glass windows aren’t too close to the sauna stove..

  15. I am thinking of building an interior sauna on an outside wall that has an existing window. Can I use the window? Or should it be replaced with something else? It is a new construction and the window is a Marvin Integrity window.

  16. Beth.. depends upon the window but my inkling is to try to use it. insulate with rigid foam and 2x2s and fir out that outside wall.

  17. Hi,

    Sorry to Hijack this thread, but I have a question about the sauna pictured above.

    Did you have to sheath the exterior in plywood and house wrap, or is the insulation right behind the T&G siding?
    Ebook has been an awesome help, but struggling with this part of the build.

    Thanks!

  18. Hi Quinn:

    Great to hear that “Sauna Build: Start to Finnish” ebook has been of awesome help for you. Regarding your question, I built this sauna in photo above, so I know the answer. For sake of clarification to your question, let’s follow the following scenario: say you wanted to put in a hot room vent, and you were standing outside wearing your Troxers, holding a cordless drill with a hole saw, ready to drill into the exterior wall.

    Here’s what you’d be drilling through:
    1. Cedar lap siding.
    2. Tyek house wrap.
    4. plywood sheeting (or maybe it was OSB, I forgot).
    5. R13 batting (between 2×4 joists).
    6. Foil bubble wrap (taped well at the seams).
    7. T&G Cedar paneling.
    8. Your buddies shoulder, sitting on the upper bench. ouch!

    Regarding #2 and #6:
    There are those who are worked up about the potential of trapping moisture in joist cavity if using both an exterior vapor barrier and an interior vapor barrier. I am not of this camp. If we build our sauna building and our sauna correctly there will never be moisture or water getting into our joist cavities. I like house wrap because it goes on in with a staple gun in 20 mins and it protects our interior walls from weather elements. I’m up for rebuttal on this, but this is what has worked for me for many years.

  19. vapor talk, my favorite! ‘vapor barrier’ is a somewhat generic term that is often applied to house wrap, poly sheeting, tar paper, faced insulation, you name it but there are differences between these products, particularly the permeance, or ability for water vapor to pass through the material. bubble insulation or kraft foil paper have very low permeability, very difficult for vapor to pass through. conversely, house wrap has very high permeability. it helps keep liquid water (e.g. rain) away from the sheathing but vapor passes through quite easily. and this is the ideal setup for a sauna. you want to limit moisture transfer from the hot room into the walls and also provide protection on the exterior against rain getting in but that exterior wall also has to breath, which is what house wrap provides. it lets any moisture that finds its way into the walls (and it will, no matter how good the construction is) a way out, keeping the wall assembly dry. so while there is a ‘vapor barrier’ on both sides of the wall, it is fine and a quite standard building technique. it would be a mistake to not have anything on the exterior and just put the siding up against the sheathing.

    vapor ‘barriers’ on both sides of the wall become an issue when both sides have a low permeance barrier, something like bubble wrap on the interior and, say, plastic poly sheeting on the exterior. this is not a good arrangement as any moisture that finds its way into the wall cavity will have a very hard time getting out, can lead to mold/rot issues.

  20. Miller: fabulously detailed. I will enjoy my hot rounds that much more, and sleep even better tonight. Thanks for this excellent info!

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