“1 R“ roughly equals to 3/4″ thick wood. According to New Alberta building standard, using normal 2 X 6 wall stud and 24” spacing, the exteria wall is roughly around R20. (Compard with older 2X4 wall stud and 16″ spacing which is only around R13)
Normally you need a R50 for your roof. below is the chart of R value of different insulation materials.
Closed cell spray foam works way better than any other materials as it has numerous closed air pockets trapped inside. And there is no convection. The material is resistant to water and keeps its shape well. However, this is the most expensive type of isulation.
Rock wool Batts are cheaper, easy to install but may loose its insulation capacity when it is soaked. But it is easy to visually check if the insualtion is good or not.
Blown-in insulation is the cheapest way to do attic insualtion, and works as expected if work is done properly. However, the material is very easy to be blown away by roof convection (attic air flow). And the cold spot is not easy to be visually found as we could not see what is burried under the insulation.
As long as the workmanship is good and insulation is regular maintained, each type of insulation does its job.
R value = structure + material + workmanship + maintenance
As a home owner, you need to make sure your insulation is well maintained.