the fire rating is not independent of the primary roof covering (the material installed on top of the underlayment. It does not have a time that I am aware.
For 2 layers you will need 16 rolls. you might get by with only 15.
single ply, you will need 9 rolls. double if it's a 2 ply application
It's primary application is roofing, but it is used as moisture barrier in several other applications. I would think you would want to use a plastic barrier in your application. Local building code is a good resource for recommended moisture barriers.
216 square foot, 72 Linear feet. Remember that you must overlap by a minimum of 6 inches.
126 square feet. Yo u must overlap a minimum of 6 inches.
The paper is not sticky. It is marked to show the depth of over lap. You apply with nails. But, short gavalnized roofing nails and with thin metal disk to keep nails from ripping through, 6 to 8 per Sq. Ft. This is not meant to be a final covering. Shingles, tile etc. go on top to protect it.
2 rolls will cover that.
216 sq. ft.
216 sf feet