It is possible, but not something a reliable roofing contractor would recommend. You’ll want your metal roof to have a solid structure, correct insulation, and sufficient ventilation–but it may not have these essentials when there’s a moldering roof still installed beneath it. Having the old system torn off completely before installing your new metal roof remains the best option.
IF YOU FIND ROTTEN ROOF OR SOFT ROOF DECKING, HOW MUCH WILL THE PLYWOOD COST?
This can end up being one of those hidden costs that surprise homeowners as some less-than-honest roofers might not cover this as