Across the bottom of beams I rarely screw the boards as along the beams plywood joints fasten to nothing but we mount along the boards the plywood. How to put the insulation between the beams on top of boards and probably as a vapor barrier from the bottom right to pull? 1. A plasterboard is a plaster, but from the outside - a carton, do you represent? This is how it is sometimes.
Attention to the question: On board you can apply wallpaper?
2. With plasterboard you can sheathe any house at all, but if the design is mobile, the drywall will crack. From which we can make any fancy twists on the ceiling and walls, a multi-level ceiling, round arches, reveals, in general, all with regard to finish!
3. You can cover up the gaps even with gypsum, alabaster, etc. Though there are certain rules to be followed.
4. I have never made the insulation under the drywall.
5. In the building shops a metal profile and guides are sold, you can make the ceiling, the walls, the various intricate shapes, etc.
As for the houses of timber ... A timber frame house - this is not a house of shaped timbers, it is the home of the ugly, not planed square logs where is a tow.
Attention to the question: what do you think the walls are left open or the people try to cover up them?
Where did you get such a terrible idea? What we've been reading horrible stories or what? And the houses from ordinary timbers look as well as from the other timbers, even though profiled or glued. After all milled logs made from ordinary timbers.