In article , The Night Tripper writes
I can understand you reservations.
It helps if you have some Celotex/Kingspan lying around as you can see how tough it is in compression.
As a test, I just took a spare small piece of 'tex and placed it over a couple of 18mm wide battens before adding a small board on top and jumping up and down on it. It did creak and deform by about 0.5mm at the battens so it was at the limit but that was 80kg+ over only 50cm2 of narrow contact on the battens. Scale that up to 50mm joists at say 500mm centres and the test was equiv to 3200kg/m2 so it suggests that a few
100Kg/m2 would be well within safe limits.As to alignment, if you lay the 'tex and mark the joist positions on the top foil surface with a marker pen then it is relatively easy to keep track of their positions. If you were then to align the OSB with the edges within 25mm of the joist position then I would say that was safe enough. I wouldn't even screw the boards down (unless it proved necessary) but would float it and tape the seams with good quality duct tape. Just keep the 'tex joints away from the joists.
How does that sound? It seems a lot less work that cross joisting.