Saturday, February 16, 2013

Building a Rocket Stove Sauna: Earth Sky Time Farm




Earth Sky Time is a community-based organic farm in the beautiful, wooded foothills of the Taconic mountains, just outside of Manchester, Vermont, USA. In addition to year-round sustainable agriculture, they also have a wood-fired bakery (featuring a massive Catalan wood-fired oven!) and make other prepared foods like humus and veggie burgers.

 
During the autumn and winter of 2012-2013, I was involved in the design and build of a wood-fired rocket stove sauna at Earth Sky Time, for the enjoyment of the EST community, family, neighbors, friends, visitors, etc. It was an exciting and ambitious project, and we strove to make it highly efficient, environmentally friendly, sustainably built, and locally sourced.

Below you can see some photos of the building process, from the laying of the foundations to the first sauna we held in the finished building. We also held a workshop halfway through construction, to teach how to design and build a rocket mass heater. We had a great group of participants and during the weekend workshop, we built the rocket mass heater that would be used to heat the sauna. You can see more details on the workshop in my next post, Rocket Mass Heater Design/Build Workshop: Earth Sky Time Farm.


The frost in Vermont reaches deep underground, meaning more work needs to go into ensuring a stable foundation is built. We chose to use simple, self-draining gravel foundations under 6 cement pilings. A system of French drains was also put in to ensure the whole site was well drained. This type of foundation doesn't need to reach below the frost line, because it allows water to drain out through the gravel. This way, any heaving taking place as a result of the frost does not come into direct contact with the cement pilings.


The building has a simple timber frame, made of hemlock from Manchester's local Alligator Sawmill. The lower sills are half-lapped, and rebar stakes join the pilings to the sills and posts. Then the sills were mortised out a bit and the floor joists were dropped in. We used hemlock 2x6's for the rafters, birdsmouthed over the top plate. They were spaced 1 foot apart, to ensure we would have a strong base for the green roof.


We finished decking the roof in time for our workshop on how to design and build a rocket mass heater, which I co-taught with Tristan Reaper. We had a really great group of participants, and it was interesting being able to shape the building around the stove. It gave us the freedom to incorporate new features into the stove that I hadn't done before, like building a diagonal feed that passed through the wall of the sauna. You can learn more about the workshop and the rocket mass heater we built in my next post, Rocket Mass Heater Design/Build Workshop: Earth Sky Time Farm.


The week following the stove workshop, we went out and got all the EPDM rubber we would need for our green roof from Brattleboro's ReNew, a nonprofit promoting sustainable construction by selling second-hand building supplies. We attached the rubber to the wooden decking with Geogreen, a (supposedly) environmentally friendly roof bonding sealant, and spliced together the long rolls of rubber with adhesive. In the photos you can see the plant box component of the green roof forming short walls along the edges of the roof. This will later function as a giant plant box, holding the green roof in place on the sloped roof while ensuring the building is dry underneath.


Next we waterproofed the walls and sided them with pine, board-and-batten style. We insulated the walls with rockwool, a fire-resistant mineral insulation that offers a more environmentally friendly and non-toxic alternative to fiberglass.

We also installed our low-e, argon-filled double pane windows and door. We came across some contractors one day, throwing these into a dumpster. The windows were brand new, still with the price tags on them and everything! Amazing, the kinds of things you can find in a dumpster. We took the larger of the windows and modified it to serve as the front door of the building.



A partition wall divides the sauna into 2 rooms: the changing room and the sauna room. In the sauna room, we put up a special reflective vapor barrier to prevent all the steam and moisture from the sauna getting into the walls. Its heat reflective properties adds extra R-value to the walls, too.


Over the reflective vapor barrier in the sauna room, we installed cedar tongue and groove walls and ceiling. In these photos you can also see the burly cedar frame for the two-tier benches. The walls and ceiling in the anteroom were done with pine shiplap.


The exterior was finished off with some battening, trim, and some lime green paint for style points.

And finally, we have the photos of the finished sauna!



In some of these photos you can see the small vent in the north face of the sauna, which can be used to release excess heat and steam from the sauna. There is a matching vent in the interior door to the sauna room. These two vents can be used together to draw fresh, cool air into the sauna and cycle out the hot, steamy air.


The secret closet in the anteroom operates by pulling out a little peg to release the false shelving, which swings upwards and rests on an opposing shelf. The closet was sized to fit a mattress, in case any members of the community wanted to take advantage of the super-insulated, cozy building during the cold winter months.


We had held a sauna the night before these photos were taken, during which the sauna room maintained an easy 145 degrees Farenheit (62 Celsius), due to the spectacular performance of the rocket mass heater. The exterior temperature that night was around 15 degrees F (-10 C), and we left the vents closed to protect the masonry from cooling down too quickly. To our surprise, when we returned to the sauna the next morning, it was still holding at 110 degrees F! (43 C). This is a testament to the tightness of construction, the great insulation of the building, and the high thermal mass of the masonry bench. The bench absorbs the heat from the exhaust gases of the stove, and radiates the heat back into the room, rather than letting it escape up the chimney. You can learn more about the rocket mass heater used in this sauna in my next post, Rocket Mass Heater Design/Build Workshop: Earth Sky Time Farm.


Building the Rocket Stove Sauna at Earth Sky Time was a great experience, from start to finish. The welcoming, community atmosphere of the farm really kept me inspired throughout the building process. I hope it will serve to bring people together and bring happiness to their community for many years to come.

- Ben


22 comments:

  1. Ben!!! It's a work of art. In shock how much you accomplished since I saw it in January. Really beautiful work.

    ReplyDelete
  2. omg. my jaw just dropped. That is soo professional, well crafted, and beautiful. I'm really impressed. I had no idea it was going to look like that! Absolutley FANTASTIC!!!!! I'll have to come back now, just to try it out xxx

    ReplyDelete
  3. Speechless! Turned out really well Ben, stunning interior! Nice site, too, hadn't seen it before!

    ReplyDelete
  4. Ben! it came out amazing! I can't believe that it's actually up and working! I hope all the nerves were worth it!

    ReplyDelete
  5. Hermoso!!!! Muy bien hecho Ben... Can't wait to try it out someday. Abrazos de Chile.

    ReplyDelete
  6. 62C is a bit low for sauna... can it reach 80-100C?

    ReplyDelete
    Replies
    1. Hi John, thanks for the question! The sauna at Earth Sky Time was built to accommodate a community of up to 15 people, including families with children. So we built the sauna room to be large and to offer a variety of heights and temperatures so everyone can find the spot they like.

      The cedar bench has 2 tiers, the higher tier being noticeably warmer than the lower tier. The room also changes in temperature from side to side, with the rocket mass heater's barrel emanating extreme heat. If you sit across the room, beneath the windows, the temperature is noticeably cooler.

      The temperature readings we took during our initial tests were taken from the center of the room, and we didn't bother maxing out the stove. Given the awesome power of the over-sized rocket mass heater, combined with the high insulation value and tightness of the building, I would say 80C is definitely possible, especially if you seat yourself on the upper tier, next to the barrel. Higher temperatures than that could be reached in a rocket stove sauna by simply building a smaller sauna room.

      Delete
    2. my sauna (infrared heat...) at home can only go up to 65C...since when is 80-100C normal for a sauna?

      Delete
    3. Hi Nick, I'd say the range of "normal" sauna temperatures is from 60 to 90C, depending on what the participants prefer. 80-100C is definitely very hot, even for a sauna, and could be dangerous. Some people prefer even higher temperatures than that, but I'd say be careful!

      9 Rules of Sauna Safety

      Delete
  7. wow, Ben. I am really impressed . Your site is great and the sauna turned out awesome!
    Maybe Candlewood needs one in the woods?

    ReplyDelete
  8. That’s really great, Ben! People prefer different temperatures, and it’s a good thing they can choose a spot where heat is subjectively comfortable. It can be of service to several people all at once.

    ReplyDelete
  9. 80-100 CELCIUS normal for a sauna?
    you have got to be joking.

    People can and have died at that temp.

    ReplyDelete
    Replies
    1. Oh no. As a native finn I can assure you that 80-100 C in sauna is quite normal and by no means extreme. I go to sauna normally twice a week and I prefer around 90 C. As a kid we used to go to sauna almost daily and my grandfather used to heat the sauna to 100-120 C. I'm still very much alive and kicking so your assumption is proven wrong.

      Delete
    2. Celsius to Fahrenheit conversion is F= (C * 1.8) + 32. 80 degrees C = 176 degrees F. I know some like it hot but that's ridiculous.

      Delete
  10. It's a nice information about the Rocket Stove Sauna.Thanks for sharing.Can you tell me the price of that stove.This blog is very informatics .Thanks.
    http://www.heaters4saunas.com/

    ReplyDelete
  11. holy bonkers your sauna is wicked awesome. it is absolutely gorgeous! i would love to get away to a place like this and just enjoy peace and quiet!

    ReplyDelete
  12. Brilliant. I'm leveraging a RMH instead of a traditional wood burner for sauna- My colleague asks about how stones/depth of stones is working out with the barrell. She is concerned that water on metal is not the right kind of steam... any comments? Can you also advise on the 'clearance' and insulation depth you used between burn chamber and wall? An important consideration that i'd HAVE to get right! (i have experience of RMH building but never through a wall!) Thanks.

    ReplyDelete
  13. For steam, do you just pour water on the rocket heater drum?

    ReplyDelete
  14. Can you please provide a simple diagram or plan on how the stove works?

    ReplyDelete
  15. Wow so cool! This is exactly what my housemates and I are trying to do in our yard. How far away from the walls did you put your heater?

    ReplyDelete
  16. Looks very cozy! Like the fact that it's made to accommodate 15 people! Great Job!

    ReplyDelete