Complete roof replacement means that the existing roof is torn off down to the plywood. The plywood is inspected for defects or dry rot. An Ice and Water barrier is used to cover the entire roof and then that is covered with a synthetic underlayment. The roofing material is installed, usually composition shingle or metal panels. All trim is replaced with 24 gauge painted steel, including eaves, sidewall, and valley. The plumbing vent flashing is replaced and painted.