Re: Building Sleeping Loft - Advice ?
I would really think hard about the possibility of using some other pre-built structure to use on top of your roof. I know it presents issues but it really is a nice way to go. The structure independent of the bus has been previously engineered to be solid. A VW van is an idea but I have seen people use aircraft fuselages and the like as well. Perhaps a farmer friend with a tractor and a welder would be a good help. If you do build from wood then you need to design it VERY carefully. Wood likes to stay still and when you introduce the movements of a vehicle things could go very bad.
If I were forced to build from wood I would use 2X2 (actually 1 1/2 X 1 1/2) to build a box on top of the roof with all sides of this box slanted. So from each side it would look like a trapezoid. Then within these walls put 2X2 webbing in the form of many triangles (the strongest shape is a triangle). Use plywood to sheet in both sides of this structure with any joints in the plywood landing directly on a web or frame member. Insulate inside the wall with extruded or expanded polystyrene (extruded has better R value). Don't forget to put vapour barrier on the inside of the wall before plywooding. And Pixie, glue the ever living crap out of this thing. There is a glue called PL 400 meant for subfloor attachment and it is very strong, could also be called PL Premium. Every connection you make, glue it, even the connections to the steel part of the bus. Finish the outside by caulking all joints with a top quality paintable caulking then paint the thing with marine paint, at least two coats. This is at least how I would go about it. This should give you a structure that won't move too much and be weather sealed. Good Luck. If your ever in Manitoba Canada let me know, I would love to help.