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Design Considerations For a WOFATI/Oehler/Earth-Bermed Home

Posts: 538
Location: SoCal USA
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Hello all! I've been pondering layouts for an Oehler-inspired home that would be in zone 6, getting below freezing temps for extended periods. I was hoping for some recommendations about design considerations for a homestead/home in the country, as far as what you found to be useful or wish you had based on your experiences.

So far the moving pieces I've scribbled on my notepad include the following:

- The base design starts with Oehler's PSP system;
- To improve thermal performance, a PAHS "thermal umbrella" consisting of 2 layers of waterproof material with several inches of insulating material in between will cover the roof and extend out from the walls with an appropriate slope for water drainage away from the structure;
- A passive air tube could be included under the thermal umbrella, with both ends screened for bugs and including a black chimney to induce a draft during the summer to heat up the thermal mass, and then the ends are sealed during winter to limit heat loss;
- A balecob (strawbale walls for insulation, layer of cob on the interior surface for thermal mass) wall for the exposed wall surfaces;
- A rocket mass heater for heating of course!
- A rocket oven based on the current kickstarter plans, perhaps one inside and one outside for summer cooking? Same for rocket stoves for cooking;
- The roof extends several feet beyond the southern wall to totally shade it during the summer, but allows direct sunlight through the windows during the colder months;
- Perhaps building a greenhouse off that roof overhang as this wall will be facing south, so it would have an earthship greenhouse feel, and provide a good space for starting plants from seed before the last frost and sprouting seeds;
- A properly draining green roof prevents capturing that rainwater for drinking/sinks/shower, but mounting solar panels on a metal roof used as a car port and/or tractor shed and adding gutters to that for capturing rain/snow;
- Installing a cistern to store captured rainwater at the highest point on the property (20 acres with about 15-20 feet of elevation change in total, pretty flat) to use gravity as at least a backup to a pressure tank powered by solar, and insulating that space to prevent freezing during winter-perhaps under the PAHS umbrella? A well would also be used to fill this cistern when it gets below half full, so there's some water if the well fails;
- Using a composting toilet system, perhaps Humanure to allow indoor use with outdoor composting;
- Having shower and sinks drain from the house into a graywater system, with mulch beds feeding willows, bamboo, or some other zone 6 hardy plants year-round;
- Hot water would be provided with wood heat, either on the RMH when heat is desired, or outdoors using wood or solar when it's warmer out;
- When feasible, making biochar when burning wood for hot water, I've seen some 55 gallon barrel designs where a pipe feeds the gasses back down to the rocket stove burn tunnel that's heating the otherwise sealed barrel of wood;
- A root cellar that goes several feet down attached to the house, and under the thermal umbrella, with insulated door, and perhaps its own air tube straight out to improve air flow;
- A pantry area or a couple shelves for storing canned food and bulk items, and enough counter space or tables for canning season;
- Other thoughts as I remember them!

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I really like your ideas.

Not exclusively to this one aspect, but the one that struck me the most in my early-morning-pre-coffee-sleepy-funk was your thoughts on making biochar while also providing heat for the structure. Most of the time trying to do multiple functions at once means whatever it is, does neither really well. For example my dual purpose sheep. They are not great at bulking up for meat sales, but are not the best wool producers either, but they pack on the weight better than a sheep bed for wool production, and yet have wool clips better than meat breeds of sheep.

And so it is with making biochar. Because with biochar a person is trying to limit the amount of heat (and thus consumption) it would be challenging to make biochar and heat a building, but in the case of an underground structure where heat will be required, but not in massive amounts due to the thermal mass effect, it might work well. A slow simmering type of heat that constantly produces biochar without overheating the structure. In theory it sounds like it would work.
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