Roofing, greenhouse room and other questions

Hi,

I'm in the beginning stages of planning out an earthbag home. I am planning on making it using as much passive design technique as possible. I was wondering what the best kind of roofing type and angle would be best for this. The home is rectangular, the roof is a skillion design and I want to put water cisterns at the lower end for rain water collection. How do I calculate the necessary overhang for my roofs? I am also thinking of sinking the home about three feet down to help increase the insulation and, if the dirt is suitable in that area, provide me with some dirt to work with. I was wondering if there would be any unforeseen problems with doing that? I'm also taking some ideas from earthships. The pertinent one being the greenhouse. I live in North Carolina, where it is too hot and humid to fully utilize this idea. But if the "greenhouse" section of the house had windows that were about 4' tall instead of the full length of the wall (the other 3' is going to be buried anyway) and the corresponding walls leading into the rest of the house had similarly sized windows, would that eliminate the problem while still allowing me to grow plants in there? I included my rough sketches with some notes scribbled on them.

Thank you,
-Alex

Lots of questions.
Where are you located?
What soil type do you have?
Is it suitable for earthbag?
What equipment to you have or will hire?
If you are digging in 3 feet, are you pouring a concrete ring beam at the lower level to carry the earthbags?
Have you though of installing post and beam wall sections so a roof can go on quickly and then infill the panels.
It will give you shelter, shade and even water while you are working.
Aim for high ceilings at least 3m.

What size water tanks are you planning?
I suggest at least 20,000L tanks  x 2 if possible
What is the average rainfall in your area?
What rough roof size do you have in mind/
I would encourage a light coloured colourbond steel roof.
See my signature for ideas about capturing and using rainwater.

I would reiterate, don't try to have earthbag walls in direct contact with soil. Or any unstabilized earthen walls. You need a foundation for that, something like stone or soncrete.

My house is mainly heated by an attached solar greenhouse. In a climate with a very cold winter, and a very sunny summer. The school I lived at for over 20 years had several buildings heated the same way. We use UV resistant plastic film for the greenhouse, putting the plastic up in October and taking it off in May. Otherwise overheating in summer would kill any plants inside and make the house uncomfortable.

I love having a growing space attached to the house, but people who want something that doesn't need seasonal installation seem to prefer variations on the Trombe wall idea. That works well, too.

My pantry is as far from the greenhouse as I can get it, since heat and humidity are bad for food storage. So it's along the north side of the kitchen, as a long skinny walk-in closet. It acts as a thermal buffer zone for the kitchen. The pantry goes down to 2 to 6C in winter (30s F) so it becomes like a big walk-in fridge. The fridge is in there, too, so in winter it barely has to work to keep the fridge at a stable temperature and the freezer frozen.

This post has a link to help with how to calculate for your roof overhang:

https://permies.com/t/174169/Passive-Solar-Design-Roof-Overhang#1367089