I was needing to know how long it would usually take for a roof to leak threw completely in one certain area , to the point of caving in the sheet rock and insulation, and causing what looks like dry rot on the exposed roof. Can you give me an estimated amount of time.
Thanks

A lot depends on the type of roofing material or shingles that were put down. A 35 year shingle should last for at least 35 years. Once a shingle or roof fails the rot will a few years at most to rod the deck. The drywall and insulation would likely be ruined immediately and not have to wait for any rot to take place.