1. How high/when do I start putting in the joists?
How much headroom do you want below the loft? That is the height where you start setting joists.
2. How high could the center point of the roof be?
The higher the center is relative to the sides, the steeper the roof will be and the better it will shed rain and snow. How much rain or snow do you get?If you have no center post, the roof rafters will push outward on the tops of the walls. The flatter the roof, the more it will push out; the steeper, the less it will push out. The loft floor framing will counter the thrust of the roof rafters, but if you have tall loft walls, those walls will have to resist the thrust by themselves. Short loft walls, or even no walls at all above the loft floor, combined with a steep roof for loft space, will be strongest.
3. How do I make the flooring for the loft?
You will need loft floor joists spaced not more than a half meter or so apart to support the flooring. All dimensions depend on what kind and thickness of floor planking and joists you can get, and no
answer is possible without more detailed information.
4. What's the highest reccomended center roof height, so that we can make the loft roomy?
There is no way to answer this without more detail. How much of the loft do you want to use, and how high does it need to be around the edges?
5. We plan to make a 10m diameter earthbag home later on as a second iteration. Would a loft be possible in this diameter??
A loft is always possible. At 10m you will definitely need some support posts from the ground in the interior, but size and location will depend on many factors.
