Ben's Natural Building - A Rocket Mass Sauna


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Ben's Natural BuildingSaturday, February 16, 2013

Building a Rocket Stove Sauna: Earth Sky Time Farm

 

See u there guys!

 


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
 

 
 
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