Anyone have experience with the envelope for a standalone exterior sauna? What is the optimal wall section for this structure? This is for US climate zone 4c (but also 5 in all likelihood for another project too).
Finlandia Sauna recommends a (outdated?) traditional residential style wall with a radiant barrier at the face of stud: 2x4 framing with glass fiber insul, radiant barrier @ inside f.o. frmg, shtg, wrb, then cladding sys. [Tho, I think this has been their recco since opening in '64...]
I'm wondering tho if there are benefits to a higher performance wall in the unique environment of what is usually a pretty dry interior, even with the steam from people & dousing rocks. Also, the environment will go through hard cycling as the sauna gets used and then sits quiet til the next session. The other part of it is that this is a structure that will have direct vents to the outside during non-use hours so humidity will fluctuate with the outside environment (tho maybe not cycle as much or as fast). [For safety, I think we can't damper the vents but maybe people do?]
Pros for improved envelope: maybe allows heater to work less hard since energy isn't rushing to the exterior (draws less energy over time, etc)? Maybe allows wall assembly/cladding to not go through heavy temp/humidity cycling because of the heat-induced vapor drive?
Cons for improved envelope: it's not an inhabited structure; don't overthink it -- millions of Finns can't be wrong; or just cost of assembly?
Thoughts from anyone who's done this on a project or lived with one?
You are wayyyyy overthinking this. Do what your heart, budget, and by-laws allow. No matter what you do, it's not going to be perfect, because there is no perfect.
I recommend going for a sauna. I don't know about you, but my brain slows down about 4 minutes into any session, and that's the important part.
I used to practice in northern MN. Climate zone 7. We would use 2x8 wd studs with mineral wool insulation in the cavity and class c vapor retarder on the face. Keep in mind this was ten years ago. My collages that still practice in MN now use R-20 continuous insulation over 2 x 6 wood studs.
In this situation nothing. The reason is you want the dew point to occur within the rigid insulation and not within the stud cavity. In typical wall assembly I'll add 1 1/2" of closed cell spray foam insulation. That way it will seal up any fasteners and act as a vapor retarder.
Regardless - R-20 ci will out perform an R-28 stud cavity insulation by around 22%.
Some will. I don't due to the 115 F temperature swings where my work is.
Sep 3, 24 1:25 pm ·
·
proto
@chad, with the radiant barrier inside the stud wall (for reflecting heat) in a sauna, it seems like any layers going outward want to breathe since, the foil won't allow drying inward
The system I described would still breath. The issue is that you don't want exterior water vapor to condense withing the stud wall. In addition, the radiant barrier is typically a class C vapor retarder so it still allows some vapor movement.
Sep 3, 24 4:04 pm ·
·
BulgarBlogger
Why not build a double stud wall (a dual envelope)? The inner envelope would be lined with a vapor impermeable membrane, while the outer envelope would be lined with a vapor permeable membrane? The gap between the two walls would be vented to dry out the cavity and lower its humidity. This way you can contain the humidity within the sauna while ensuring thermal continuity of the envelope?
Vapor Drive is a function of how heat is transferred through the building envelope. The double stud wall cavity effectively acts as a "thermal break" in the envelope, allowing for two different due points to be reached.
Excellent idea BB! The double stud wall would be more labor intensive to build than using CI though.
I don't believe you'd want to use a vapor barrier on the inner wall. Typically a class c vapor retarder is used for saunas. In a traditional dry sauna you're not dealing with much humidity. It's a very dry heat with humidity under 10%.
That does bring up a good question - what type of sauna is this?
Exterior wall assembly - exterior sauna
Anyone have experience with the envelope for a standalone exterior sauna? What is the optimal wall section for this structure? This is for US climate zone 4c (but also 5 in all likelihood for another project too).
Finlandia Sauna recommends a (outdated?) traditional residential style wall with a radiant barrier at the face of stud: 2x4 framing with glass fiber insul, radiant barrier @ inside f.o. frmg, shtg, wrb, then cladding sys. [Tho, I think this has been their recco since opening in '64...]
I'm wondering tho if there are benefits to a higher performance wall in the unique environment of what is usually a pretty dry interior, even with the steam from people & dousing rocks. Also, the environment will go through hard cycling as the sauna gets used and then sits quiet til the next session. The other part of it is that this is a structure that will have direct vents to the outside during non-use hours so humidity will fluctuate with the outside environment (tho maybe not cycle as much or as fast). [For safety, I think we can't damper the vents but maybe people do?]
Pros for improved envelope: maybe allows heater to work less hard since energy isn't rushing to the exterior (draws less energy over time, etc)? Maybe allows wall assembly/cladding to not go through heavy temp/humidity cycling because of the heat-induced vapor drive?
Cons for improved envelope: it's not an inhabited structure; don't overthink it -- millions of Finns can't be wrong; or just cost of assembly?
Thoughts from anyone who's done this on a project or lived with one?
You are wayyyyy overthinking this. Do what your heart, budget, and by-laws allow. No matter what you do, it's not going to be perfect, because there is no perfect.
I recommend going for a sauna. I don't know about you, but my brain slows down about 4 minutes into any session, and that's the important part.
i absolutely love a sauna paired with a cold plunge
I used to practice in northern MN. Climate zone 7. We would use 2x8 wd studs with mineral wool insulation in the cavity and class c vapor retarder on the face. Keep in mind this was ten years ago. My collages that still practice in MN now use R-20 continuous insulation over 2 x 6 wood studs.
R-20 rigid? What's in the 2x6 cavities?
In this situation nothing. The reason is you want the dew point to occur within the rigid insulation and not within the stud cavity. In typical wall assembly I'll add 1 1/2" of closed cell spray foam insulation. That way it will seal up any fasteners and act as a vapor retarder.
Regardless - R-20 ci will out perform an R-28 stud cavity insulation by around 22%.
I got that, I was just wondering if they used cavity insulation as well.
Some will. I don't due to the 115 F temperature swings where my work is.
@chad, with the radiant barrier inside the stud wall (for reflecting heat) in a sauna, it seems like any layers going outward want to breathe since, the foil won't allow drying inward
or am I not understanding how that works?
The system I described would still breath. The issue is that you don't want exterior water vapor to condense withing the stud wall. In addition, the radiant barrier is typically a class C vapor retarder so it still allows some vapor movement.
Why not build a double stud wall (a dual envelope)? The inner envelope would be lined with a vapor impermeable membrane, while the outer envelope would be lined with a vapor permeable membrane? The gap between the two walls would be vented to dry out the cavity and lower its humidity. This way you can contain the humidity within the sauna while ensuring thermal continuity of the envelope?
Vapor Drive is a function of how heat is transferred through the building envelope. The double stud wall cavity effectively acts as a "thermal break" in the envelope, allowing for two different due points to be reached.
Excellent idea BB! The double stud wall would be more labor intensive to build than using CI though.
I don't believe you'd want to use a vapor barrier on the inner wall. Typically a class c vapor retarder is used for saunas. In a traditional dry sauna you're not dealing with much humidity. It's a very dry heat with humidity under 10%.
That does bring up a good question - what type of sauna is this?
Sauna is a sauna: humidity < 10%
Those other items are not
proto - I know that - some people don't. I just wanted to be sure.
all good -- i was not intending to come off caustically...apologies!
Don't worry about it!
You’re right. I think I was thinking about a steam room.
No problem! It's still a good idea!
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