Kelly Hart and I have been following the The Year of Mud cob house blog for about 2-3 years. Ziggy, the builder and author of the blog, learned the hard way that cob (actually, earth building in general) is not a good choice in cold climates.
Kelly has been warning people for years at GreenHomeBuilding.com (the number one most popular site on natural building) that some earth building techniques are not appropriate for cold climates. We also want to make sure our earthbag website readers are aware of the limitations of building with earth in cold climates.
Kelly has an interesting story about this on his website. He stayed in an old adobe hotel in southern Colorado one winter. It was freezing cold inside. Despite the thermal moderating effects of earth (the flywheel effect), if there’s extended freezing cold then the inside temperature can be like living in a cave, because earth is not a very good insulator. That’s why most adobe houses are built south of the Colorado/New Mexico border. That’s the range where colder temperatures start to make adobe impractical. The same is true with earthbags, unless the structure is insulated.
You can find much more on this topic on our websites by searching for “insulation”, “insulated earthbag” and “cold climate”. The key is to either fill the bags with insulation such as scoria or add a layer of insulation on the exterior.
Please note, we love Ziggy’s blog and encourage everyone to check his site regularly. He has lots of good ideas, and his open, sharing approach is conducive to learning.
Hi Jeff, did you ever built your cold wet climate dome? I am interested to learn more about it….for Central BC Canada. Hope to hear from you!!!
Owen
This is off-topic a little, althou here in Florida we fall under the rainey climate area. I was wondering about the idea of surrounding the earthbags with a layer of perlite bags and using the pallet truss and round tree idea for thick trusses filled with perlite insulation over head with metal roofing into gutters into a cistern there bye supplying your own water. Seems this would be pretty efficient here in Florida. No heat needed( but install one of those Rocket Stoves) and maybe it would be cool enough you’d could get along well without air conditioning as the ground temperature coming up through the floor should keep the temp comfortable all year round. Your thoughts?
Steve
I see no reason for perlite insulation. Build wide roof overhangs to shade the walls. Use white roofing to reflect the heat.
There is no one size fits all natural building. Every building we create must be tuned in with the climate and characteristics of the locale you create your structure in. I am looking into designing and creating a cold weather dome in a wet climate. I have yet to create a prototype yet, but the chance will come very soon ;) IN short, the concept is to use a variety of methods to keep the structure warm, while using minimal extra heating. Ideally the site has full winter southern exposure.
The North side will be bermed, and have a double bag wall. The inner bag wall will be composed of an adobe like soil fill, the outer row will be filled with an insulative fill such as Scoria (They call it Red Cinder Rock in Oregon) up to the top of the berm. From there, the plan is to use the lava rock in the rows up to the top.
The South side of the structure will be a single row of an adobe like mixture, with an attached greenhouse, to heat that wall.
The achilles heal of domes is water infiltration. Typically domes have been plastered all the way up to the top with a cement or lime render. I do not think this a responsible method in a very wet climate as the water will eventually find a way into the earth through cracks. I firmly believe in the importance of creating an impermeable cap.
I propose creating a 360 degree eave around the structure by embedding rebar and using chicken wire. This will be plastered in cement with the use of a vapor barrier between where the eaves meet and the structure. The Cap will be created out of metal. I am unsure of the exact materials I will use, but I am attracted to shingling large flat sheets of metal. The metal will terminate at the cement eave/gutter/planter/water filter(I plan to write this up in more detail soon). Below the eave will be earthen plaster, and perhaps a stone bench for feet. The interior will be earth plastered as well.
Back Up heat will be provided by a rocket mass Heater Bench on the inside of the dome.
Some questions I have:
Will the condensate on the underside of the metal cause any problems? Should the bags under the metal be plastered or covered with a plastic sheet? Can a layer of scoria be used under the earthen floor to insulate the heated inside from the coolness of the earth?
Jeff, there’s a real need for rainy climate dome designs. This would greatly spread their use.
Comments:
– No need for a double back wall. That’s a lot of extra work. Just build the dome, put 6 mil plastic against it, then backfill 2′ or so with scoria, then more plastic, then backfill with earth.
– Scoria under the floor is a good idea.
– I would put plastic sheeting under the metal cap.