I have two layers of R19 fiberglass insulation in my attic. One layer is paper faced and installed in the rafter bays with the paper side down. The other layer is unfaced and installed across the rafters (i.e. 90 degrees to the bottom layer).
That was good enough 15 years ago when I installed the second layer, but I would now like to install at least another R19 on top of what I already have. My question is can I install another layer of unfaced R19 on top of the two layers I already have? (I worry that this might compress the two lower layers.) If I can should I install it at 90 degrees to the top layer?
Also, is three layers of R19 enough for a cold climate (upstate NY), or would it pay to add more than R19 as long as I am at it?