Dec 14, 2015

Insulating the sauna-- I feel warmer already.

So, last time, I left off with a list of things to finish prior to insulation. Some of those things I realized I didn’t  need to do, some I rushed through and forgot to take photos, some I did and took pictures—here’s the previous list below:


  1. Create nailing surfaces on the walls for cedar boards.
  2. Nail extra 2x4s for supporting the benches in the hot room.
  3. Create a vent in the hot room—a small window (about 4” x 8”), on the wall opposite from the stove, which we can open to let the fresh air circulate (convection).
  4. Put in a junction box and run speaker cables for my in-ceiling speakers I found on CraigsList.
  5. Install attic ventilation baffles to prevent the insulation from cutting off the fresh air supply to the attic coming from the soffits.
1. The only place I needed to add nailing surfaces for cedar was on both sides of the wall that divides the hot room from the changing room. We simply added 2x4s to the existing studs to provide more surface to secure the cedar boards to later. Also, I went though and installed metal nailing plates over all the holes in the studs though which we ran the Romex wires. This is to prevent accidentally running a nail in to an electrical cable.

2. The extra 2x4s for benches we didn’t need. After doing some more research (not very thorough research), I realized that there isn’t one complete example online that I could follow. So, having gotten the general idea, I think I’ll make things up as I go. The one main point about the support for the benches is this. There needs to be a 2x4 screwed in to studs in the walls on as many sides of the bench as possible. So, for the corner bench—I can do it on 3 sides (in the back and on both sides). For the other bench, I can do it only on the back. Again, more on this later when I get to it but  what’s important now is that the support 2x4s screw in to the studs OVER the cedar—so nothing to do now.

3. Now, on to the vent in the hot room. I’ve laid awake a couple of times trying to think this through. I thought I had a good idea until I did it J First, because I have lap siding, I needed to make sure I make the hole such that it’s in the middle of the siding piece and doesn’t cross 2 of them. From inside the hot room, I measured a rough length from the side of the building to the first and 2nd studs between which my vent would be. Then, I went outside, found the placement on the siding where I wanted to be and measured the same length. Using a small drill bit—I made 4 pilot holes for the vent.  After, I went in, marked my lines connecting the drilled holes and using a multi-tool sawed through the sheathing and siding to make the vent hole. What I realized then is my plan was wrong. The cedar box that I needed to build which would make up the vent opening, had to pass through the hole I just made—not abut to it. Now I was annoyed that I made that mistake, and having planned to finish insulating that night, I ended up rushing things. I made the opening bigger without marking it first, cut out the hole, assembled my home made (slightly crooked) vent and stuck it in the opening. Once I was somewhat satisfied, I nailed in place with a bread nailer.

4. For the speaker cables, I used a regular blue electrical junction box. I hung it on the wall where I thought it would be convenient. I then ran 4 speaker cables—2 in the hot room—2 in the changing room. Now, one of the things I thought about is interference with electrical cables. Because I ran my speaker cables through the same holes as I ran the Romex, I thought there may be a hum. Looking online, the debate rages on. People recommend running speakers at least 12 inches from Romex. I neither had time nor too much space to have 12" clearance for speaker cables. So I left things as is. I’m pretty sure I’ll be OK—but even if there is any slight hum—this is a sauna—not a concert hall. I’m not worried.

5. As with anything else—opinions differ about attic ventilation. Some say you don’t need to do it, some say you must. Same with insulation in the attic. I, however, wanted to be sure my sauna was HOT. Since I won’t get a chance to come back and change things, I’ll err on the side of caution.  First, if you remember, my soffits are the vented kind. That means there’s fresh air coming in from them on 2 sides of the building. Since when I put up the fiberglass I will probably  end up blocking that ventilation, I needed to put in something to prevent the blocking. Enter Attic Ventilation Baffles.

Attic Insulation Baffles
Attic Ventilation Baffles

Attic Ventilation Baffles are simply plastic sheets which attach right to the roof sheathing (make sure your staples are not longer than the thickness of the sheathing) and create a duct over insulation for the air to get to the attic from the vented soffit. It took me a little research and trial & error to figure out how they install but in the end, I think I got it. You start by stapling the edge to the top of the top plate of your wall. Then, you bend it in so it’s horizontal with the soffit bottom and attach it to the roof sheathing above with more staples. At first they seem long, but that’s a good thing. That way they drive air over the fiberglass instead of in to it.

Attic Ventilation Baffle Installed
Attic Ventilation Baffle Installed
Attic Ventilation Baffle-- closer look
Attic Ventilation Baffle-- closer look

Finally, I went back and installed the light switches/dimmers and outlets while I still could see which Romex goes where. Make sure you have one GFI outlet and run the other outlets on the GFI circuit from it.

Next was fiberglass. There are a couple of nuances with that. First, our trusses are 24” on center. They sell 24” fiberglass, though not much of it. In the box store, the fiberglass is laid out under headings Attic, 2x6 Walls, 2x4 Walls. Under attic, the only choice for 24” they had was R38—it’s 12” thick. That would almost be to the top of the roof for me. Too much. The other choice was R19- about 6” of insulation, however, it was under the heading of 2x6 Walls. On the bag, it said it’s good for walls and crawl space. To me, attic/crawl space is the same J So—That’s what I took. The fiberglass comes in rolls that you then trim to your size. A clean way to do it is with a utility knife—a more convenient way—is just to tear it J

The other insulation I needed was for the walls. For 2x4 walls, I needed R13 Unfaced. Because we’ll be using the foil bubble vapor barrier, we don’t want to have a moisture sandwich, so we can’t have insulation with Kraft paper. This insulation comes in pre-cut batts for standard size wall. Since our sauna has a lower ceiling to retain heat—I ended up folding in the excess fiberglass at the bottom.

I started to install the fiberglass with the ceiling. Each run starts and ends on the wall top plate in the plastic cavity created by the attic ventilation baffles. Make sure the fiberglass covers that cavity very well. There’s a lot of cold air there. Then, slowly put up the fiberglass in one piece, between 2 trusses until you hit the other side of the building. Then cut the fiberglass. Thanks to gravity, the fiberglass will try to escape the ceiling to closer acquaint itself with the floor. To prevent that, you can buy special ties for $20 a pack, or you can do what I did. Simply run a piece of duct tape from one truss to another to have the fiberglass rest on. Staple the tape to both trusses for extra hold. One note of caution-- when I installed the can lights, I used specific ones rated IC-- that means they can contact insulation. Make sure yours are the same before putting fiberglass over them.

Ceiling Fiberglass- R19
Ceiling Fiberglass- R19
Duct tape holds the fiberglass in place.
Duct tape holds the fiberglass in place.
As you can see—there’s plenty of space still left between the insulation and roof for air to circulate. This is good.

Ceiling insulation- photo from above the joists.
Ceiling insulation- photo from above the joists.
  
The wall insulation goes a little easier. Simply fill the spaces between studs. Nothing tries to fall out. For the smaller spaces where there batts are too wide, you have to use a utility knife to make clean cuts. Don’t toss the pieces you cut—they’ll be useful elsewhere. Remember to cut the fiberglass around junction boxes. Also, remember that the insulation value doesn’t come from stuffing the fiberglass in, it comes from the air space created, so make sure it’s fluffy and there are no holes between it and the studs.

Wall Insulation- R13
Wall Insulation- R13
More wall insulation
More wall insulation
Better look at wall insulation.
Better look at wall insulation.
Insulating the wall dividing the hot room from changing room.
Insulating the wall dividing the hot room from changing room.

The last step before bubble foil install is what Glenn, of SaunaTimes.com , suggests in his e-book on how to build a sauna. That is, to use expending foam specifically for windows & doors and cover the gaps between the window frame and the rough opening. We put that foam in around both windows as well as the entry door. Then, whatever was left, we used to seal any other gaps which were too small for fiberglass.

Now, with the sauna looking like a room any princes would be proud to call her own, i.e. pink, it was time for the bubble foil. I should note, though it was about 40F outside, at this stage you could tell that something was making a difference. Removing one piece of fiberglass in the ceiling to adjust something—you could now tell the colder air flow in the attic versus just cold temp in the sauna.

I ordered a big roll of the foil bubble wrap online. I think it as 200sq feet and about 4 feet wide. We started in the changing room. We put the roll on the floor and stapled it to the studs carefully unwinding the roll as we went around the room. We made absolutely sure that we had each corner well creased with enough slack in the foil. When cedar goes over this, we don’t want it to tear from being too tight. Also, we marked all the outlets and junction boxes we covered with a marker so we could cut them out. This first section only covered the bottom half of the wall. The 2nd section abutted to the top of the first section and was creased at the ceiling. Initially we thought we could use that crease—but, because there was no stapling surface to attach it to, we ended up trimming it off. One important thing to remember. Our wall that divides the hot room from the changing room, only gets the foil insulation on the hot room side. The other side gets nothing but cedar. That way it can breath and not create a moisture sandwich. Again, this is one of those topics widely debated online—but that’s the approach that makes sense to me.

Foil only goes on the side of the hot room.
Foil only goes on the side of the hot room.

Once the walls are covered up, it’s on to the ceiling. Our first thought was to go parallel to the trusses, but we quickly realized that perpendicular is the way to go. So, starting at the corner where one wall intersects with the ceiling, we stapled the bubble foil and continue to staple it on every truss. Then, we cut the foil at the opposite wall to ceiling intersection. As far as stapling goes, we generally tried to put a staple every foot on the walls and slightly less than a foot apart on the ceiling. The foil will also be held in place by the cedar, so don’t try too hard. When running the foil over the chimney support box, simply get right up to it and cut the size of the support box in the foil right on the fly as you’re hanging the foil. Get the box to fit in and continue stapling. Make sure, however, that the foil sits at least half of the stud away on the stud supporting the support box. Then, tape it to the stud with foil tape. The max temp this insulation can take is 180F per the manufacturer.  

At this point, we were starting to take layers of clothes off. With a small electric radiator going, the sauna started getting a lot warmer and the windows were starting to fog. This foil bubble insulation is good! One last thing to do is cover all seams with special foil tape to make sure there’s no air leaks in the foil.

Hot room insulation complete.
Hot room insulation complete- can you see the foil tape in the middle?
Hot room support box
Hot room chimney support box
Cut out outlets and switches from insulation.
Cut out outlets and switches from insulation.

Getting so warm the windows are steaming!!
Getting so warm the windows are fogging!!

2 comments:

  1. ive been reading quite a bit on the aluminum foil vs reflective bubble foil debate. how have you found the bubble foil to perform? my main concern is off gassing (even if the product can withstand 180F, seems like things might start getting funky before then). ive already purchased bubble foil, but am seriously considering switching to simple aluminum and making up the 1-2 in R value with more insulation...any thoughts?

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  2. J,

    Thank you for following the blog! Since I haven't dealt with the regular foil, I can't really compare the two. However, my goal was to build the sauna to be as warm as possible for the most enjoyment. Although I haven't yet had a chance to use it in the dead of winter, as we were still building, we did use it in the early spring, with temp's being around 30F and were able to get the hot room above 200F.

    As far as off gassing, I assume you're talking about health concerns. I am too usually looking out for things like that, however, look at it this way:

    1. The foil will be behind a layer of 1" thick cedar.
    2. As far as I understand, it's a difference between just foil and foil with air pockets
    3. You probably have worse materials that are more exposed such as green 2x4s to frame/support your benches, and the stove which will smell up the room like crazy for the first 10 firings while burning off the paint :)

    So, my personal opinion, use the insulation that will retain the most heat in the room-- you'll love the sauna that much more if it gets you hot in the winter.

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Would love to hear your comments/ideas/suggestions!