What is the useful life of insulation, and why?
In energy auditing, the useful life of blown in insulation (both fiberglass and celulose) is typically estimated to be 15 years. (in my experience) I would like some input on why that might be. My common sense is telling me it should be much longer. I read everywhere that cellulose, unlike fiberglass, breaks down over its useful life, but nowhere can i find where it specifies what the useful life is, or why.