Earthship Modifications Feedback Requested

Hello,

I’ve become fascinated with the Earthship homes.  I love the idea that they endeavor to be  sustainable self-contained buildings that provide for all their inhabitant’s basic needs of a temperature-controlled shelter, food, water, renewable energy and waste disposal.   I’m also aware of their many issues, especially related to costs associated with the greenhouse with its additional set of double glazed internal windows to prevent overheating, labor intensive tire filling and excavation.  

I propose the following modifications to make the Earthship more affordable:
• Strawbale or earthbag construction of east, west and north walls instead of berms and excavation.
• No internal greenhouse windows.
• Shades installed where internal greenhouse windows are typically located to block solar gain while allowing plants to receive sunlight.
• Limited northern windows with lower openings for light and cross ventilation.
• Cooling tubes installed in the slab floor’s substructure.  I recognize the air would be not as cool as air from tubes excavated to the recommended 5+ feet depth.  The tubes would have intake vents in the northern foundation wall and exhaust vents in the southside greenhouse floor.  Similarly to the Earthships, the greenhouse would vent out through an operable roof exhaust vents.  One of the reported issues with Earthships is the north sides are cold where the cooling tubes vent in and the southsides are hot from the greenhouse.  I’m hoping that moving the cooling tube exhaust vents to the southside would regulate temperature disparities by improving stack ventilation.

My question for the Permies (especially those with an architecture background): Do you think the southside cooling tube exhaust vents, internal shades and north side windows are enough to regulate the temperature without AC?  I’m thinking it may not.  If that’s the case, the alternative is:
• Southside eave (actually lower part of solar panel) to reduce summer solar heat gain but will also result in insufficient sun light for summer vegetables grown in the greenhouse.
• External raised garden bed against the south wall for summer garden.  
• Internal raised garden bed for winter garden.  
• Raised garden beds will provide 2-4 feet thick insulation of southern wall.

If the modifications don’t make sense, I can post a sketch later.  

Please let me know if you think I’d receive a better response on another forum.  Biotectecture’s (Earthship company) forum doesn’t seem to get much action.

I look forward to reading your thoughts.

Thanks in advance.

Strawbale construction would not work where one side is buried below grade, both from a structural perspective and moisture control. Strawbales have minimal strength as retaining walls to hold back an 8' earth bank. You would need some other means for that. Strtawbales except in a desert-like environment would rot quickly with one side against the earth; even with a waterproof barrier on the outside, moisture would move through them from the warmer inner face and be trapped at the cooler outer face and accumulate, dooming the bales.

Earthbags might be viable, depending on the climate and the specific methods for excluding water on the outside.

The greenhouse glazing on the south face of an earthship is one of the biggest features and one of the biggest drawbacks to my mind. Solar gain is great when you want it but fatal when you have too much. An overhang to control overheating in the summer would be essential if you can't depend on cool nights every night in the summer to get rid of excess heat, as happens in desert climates but not in temperate or moister climates.

I would certainly use raised beds outside for summer growing. Raised beds along the greenhouse wall would reduce the amount of solar gain by reducing the amount of glazing, which is a matter of balancing the requirements in all seasons. You would need to calculate heat gain/loss year round and plant light needs to decide what is best.

Earth tubes and other ventilation/heating/cooling methods are another level of complexity which I don't have expertise on.