Home Design - D Dome

Hi everyone,

I'm at the designing stage of an earth-bagged home and would like some opinions on the design. Please refer to attachment.
The design consist of a center large dome being the major living quarters and the outer small dome (ring) being a greenhouse. Light enters via the front made of glass which faces south.
The entire house will be bermed into the earth as much as possible, except for the very front. Let us forget about insulation for now.

My concern regards water between the center dome and the ring dome. The foundation will be a large rubble trend / pad.
I'm thinking with the two domes being tangent to each other, that I should incorporate another rubble trench in this area to divert the water, just the same as I will with the foundation. I'm thinking this is the best solution.

The alternative is to separate the two domes using the foundation rubble trench to divert the water. The issue with this is how far apart and this simply makes the outer ring dome larger in circumference which means more material....I opt for the first solution.....what's your opinion?

Thanks,
P