Build your own sauna with a sloping roof - suggestions/notes/plans

Hello! [IMG alt=":)"]https://saunabauen.de/forum/images/smilies/icon_smile.gif[/IMG]

I want to start this thread to get help and feedback on my planning for a DIY sauna. Of course, the thread can also be used for all topics related to sauna construction.

We decided to get a sauna, and since a kit is not an option and a custom build is too expensive, I decided to take it into my own hands.

When we built our house 3 years ago, we reserved space for a sauna at the very top by the roof terrace. Unfortunately, instead of a planned flat roof, we had to implement a shed roof to get the building permit.
This results in a roof slope with a knee wall height of 1.81m clear height.
A floor area of 2.10m width and 1.91m depth is available.

The height is further limited by an air supply vent on the higher side. The air supply vent is positioned at a bottom edge (UK) = 2.05m above the finished floor level.
My idea now is to execute the top edge (OK) of the sauna at OK=2.05m in order to access the vent if needed. According to my planning, I would still have a clear height inside the sauna of 1.995m.

The sauna is surrounded on 3 sides by an exterior wall (Poroton T9 masonry).

The ceiling is installed without counter battens directly on the beams and the vapor barrier. This was necessary because otherwise, we would not have been able to open the terrace door. The architect dropped the ball here... : [IMG alt=":roll:"]https://saunabauen.de/forum/images/smilies/icon_rolleyes.gif[/IMG]
The floor consists of fine stoneware tiles on screed with underfloor heating.

There is a three-phase power supply with 5x2.5mm² cable. The cable length is about 20m. According to an electrician, the cable should not pose any restrictions for the project.

Since it is going to be quite tight anyway, I want to keep the wall construction as slim as possible.

Planned wall construction:
1. Masonry with plaster
2. Vertical battens (24x48mm) with 24mm air gap for ventilation
3. OSB boards 15mm
4. KVH 40x60mm, positioned so that the 40mm accommodates insulation
5. 40mm wood fiber insulation in the cavity
6. No vapor barrier
7. 15mm profiled battens mounted horizontally

Now my questions:

1. Is my wall construction feasible as planned, or is it too tight? This would give me a finished interior dimension of about 1.92m x 1.75m.
I am 1.84m tall, so I would still have space to lie down.

2. We would like to install a full glass door with a side panel to have a view outside.
We plan to use 8mm tempered safety glass (ESG). Is this possible, or are there issues with the stove?

3. How is the glass wall connected to the sauna? I thought of giving the KVH a groove all around so the glass can be fitted in there. Is that possible?
On the floor, I read somewhere that someone placed the glass on a silicone mat, which was then cut flush. That's how I imagine doing it as well.

3. The sauna has an area of 3.34m² and an interior height of 1.995m. Ignoring the slope, that results in a volume of 6.66m³.
I have read that for a glass door, you should add 1.5m³, and for a glass wall, add the surface area (1.5m²) multiplied by a factor of 1.2 as volume.
That would result in a total volume of 9.66m³, and I have correspondingly chosen a stove with 9kW. Does that sound right, or is it oversized? Currently, I am leaning towards the "Harvia The Wall" with external control.

4. Because of the stove's position, I actually don't have space for a stove guard between the glass wall and the stove. Is that necessary in private saunas? I am not too worried about it, but my wife is a bit concerned.
The alternative would be to shift the lower bench a bit under the upper bench and move the stove, then there would be space for a guard.
Alternatively, there is an illuminated protective glass panel for the above-mentioned stove, which is mounted on the front side of the stove. Would that be enough? I am not so keen on the wooden constructions... [IMG alt=";)"]https://saunabauen.de/forum/images/smilies/icon_wink.gif[/IMG]

5. A work colleague recommended bench heights of 60 and 120cm. However, I would have problems with the sauna height if I do that. I would go for 45/90cm. Since we both don’t want it too hot, I see no reason to go higher?

6. To avoid further reducing the roof slope height, I want to skip the OSB boards there and mount the KVH directly at a distance of 24mm (battens) to the ceiling. Do you see any problems with that?

7. We simply like it much better if the profiled wood is mounted horizontally. Is there any objection to that? Due to the tight situation, I would forgo any additional ventilation. From what I have read, that is not necessarily required.

8. Would it make more sense in my case to use a different material + vapor barrier instead of wood fiber insulation?

9. The wall to the left of the plan with the glass door should also be clad with profiled wood on the outside. That way, I could build a service opening above the sauna to access the air supply vent if needed. Also, I could place the electronics for lighting and audio on the ceiling, making them accessible.
Can I mount the profile boards directly on the KVH, or is an additional counter batten or similar needed?
I want the wall to finish flush with the door jamb of the terrace door. To prevent the terrace door (especially the handle) from hitting the wall, I would place a stopper mounted on the KVH there.

That’s it from me for now, I am curious what you think of my planning. I hope my post isn’t too long... [IMG alt=":?"]https://saunabauen.de/forum/images/smilies/icon_confused.gif[/IMG]

Attached are a few pictures to show the planning status. If you need any more info, just let me know.

I look forward to any feedback [IMG alt=";)"]https://saunabauen.de/forum/images/smilies/icon_wink.gif[/IMG]

Thanks in advance!

Regards

Nice project. Something like that is still ahead of me someday.

The stove with 9kW is correctly chosen. The circuit must additionally be equipped with a 4-pole RCBO 25/003A to be on the safe side.

Depending on the length of the cable, lay at least 5x2.5mm² (if not already present) and protect with 3x16A.

Thank you, the cable is 5x2.5mm² approximately 20m long. It is also separately on 3x16A fuses.

The big question for me is about the wall construction, whether everything will work out. Since the area is quite limited, every centimeter counts...

Yes, that's what I thought as well. However, I would leave a bit more air gap to the house wall and definitely build with a vapor barrier. Why the decision/thought to do without it?

Otherwise, the wall structure is fine.

We also had such an idea back then and more or less just started. We doubled the 3 concrete walls in the basement with 6x4 and almost made the front entirely glass. Between them insulation and above that an aluminum skin, battens, and the profile boards. We made the benches individually and especially wider out of sauna wood. In my opinion, the wall construction is sufficient; even our later outdoor sauna had only a 44mm wooden wall and an 8kw stove, and everything was fine even in the deepest winter. We had double-pane window glass (for whatever reason?), the pane next to the stove will of course also get hot from the outside, and I wouldn’t want that. Additionally, you see the stove from the outside and also a bit under the bench; therefore, I would consider cladding/plastering the lower half normally and placing the glass only at the top. That way, you eliminate the heat problem there and don’t see any less outside; you could possibly hang the stove on the front wall then.

The glass connection either like this or you work with very small square battens on both sides to hold the glass. We had the KVH run straight through below, practically as a sill, and placed the glass on that. The sill also had the function that the sauna door shuts against it, but that’s a matter of taste; we did it more by learning by doing at the time. The 9kw stove should definitely be enough, we also had the steam function, as we don’t always want it that hot. In addition, the sauna is indoors, and you already have a certain temperature in the room, not like outdoors. The stove itself is hot everywhere, and even with purchased protection or something else; you have to be careful anyway, but that’s always the case. Therefore, I would forgo extra measures there.

We also thought endlessly about the height. In the end, we sat in it when the room was finished and proceeded by feel. In my opinion, you should be able to sit comfortably upright on the upper bench and still have some pleasant centimeters of air to the ceiling. The seat height of the bench results from that by itself; you can choose this however you like. Horizontal installation of the cladding is also possible, and I see no problem; as I said, the stress is in a private setting and not 12 hours per day continuous operation/moisture. Therefore, things like insulation, ventilation, and moisture are important but you are always there yourself and pay close attention to these things. We had our sauna in the basement for years without any problems with mold or moisture. You also have a door to the outside next to it, the sauna door itself can be left open after sauna sessions or during the day, and if you have a few centimeters less insulation, then the sauna session costs preheat temperature—simply put, 50 cents more electricity. I would want the centimeters more inside in your place, and if you lay the aluminum skin or something similar, no moisture will get through anyway. Your plan already considers many things, and I wouldn’t hesitate to implement it that way. I would want a steam function on the stove, though, because we don’t want it that hot. Regarding audio, we installed it under the bench on the floor. It only gets lukewarm there, and theoretically, you can place or install a WiFi speaker or the like there.

Wow. thanks for the helpful feedback! Regarding the steam function, you’ve got me a bit excited again, we’ll have to rethink that. Thanks for the hint about the audio. I’ll probably go for a Sonos Play1, which is also suitable for humid rooms, place it on the floor under the bench and that’s that. You mentioned it: the design is important to us as well, which is why we originally wanted to do a complete all-glass front. But since that would take away the possibility to place a dresser on the deeper side, we recessed the glass wall.

Basically, I think the idea of a window above the stove (with the stove then on the wall with the door) is not bad at all, but wouldn’t it get even warmer than if the stove is as planned now? The advantage would definitely be that the stove is further away from the benches. I still have to think about it.

Yes, that’s what I thought too. However, I would leave a bit more air gap to the house wall and definitely build with a vapor barrier. Why the decision/idea to do without it? Otherwise, the wall construction is fine.

I actually want to avoid enlarging the air gap. As I said, every extra cm is basically too much... But I will probably play it safe and use a vapor barrier. What insulation material I use then, I still have to think about, I don’t want to touch itchy mineral wool :D Let’s see what else is available.

What’s the opinion on the exterior cladding of the visible wall? Can I screw the profile battens directly onto the KVH, or should I provide a counter battens or something like that? That determines the usable depth of the interior cabin, so it’s a bit urgent for me... :D

I would also be interested in an opinion on the missing OSB board at the ceiling slope. However, I am now indeed reconsidering it; it’s only 15 mm of height I would lose there, it’s not a big deal, I think.