IF I AM REMOVING A BUR ROOF TO EXPOSE THE METAL DECK. I WOULD RECOMMEND ADDING A MINIMUM OF 1.5 INCHES OF “ISO” R-value = 8.6. But getting back to the question . The R-value of three inches of “ISO” IS 17.4
You answer your question.Its one of the highest R-Vaule insulation on the market pound for pound.
You asked the question and answered it at the same time. Good Luck.