I am looking to add insulation to my attic. www.owenscorning.com recommends R-49, however the closest I can find is R-38 and that's 12 inches thick which almost doubles the height of my rafters. I currently have 3 inches of blown insulation in my attic. Is it ok to go higher than my rafters? If so, how do I walk through my attic without being able to see my rafters?