(I'm really not trying to sound too insulting but there are so many holes in your game plan, I can't but help shake my head knowingly and wait for the disaster 'what do I do now' post.[/quote])

Markus,

Check my original post and note that the foam insulation is applied to the underside of the roof decking, not in the floor joist cavities.

The floor joists for the upper level are full-dimension old growth softwood that is very dense. The new joists to be sistered will span from exterior wall to center supporting wall and will be joined using construction adhesive and carriage bolts and/or lag screws. Shims will be installed to support the new joints at the supporting walls. Also, I may have misrepresented the use for these rooms as "living spaces". They actually will be bedrooms.

As to the bathroom, the tub is a light-weight Sterling 4-piece unit and, yes, if a person wanted to waste water with a tub bath, the floor joists would be stressed beyond 40psi for a short time.

That you for your generous, kind hearted remarks.

John Lampert