When your roof is fully replaced, the old shingles are stripped from the roof, exposing the deck. An underlayment or felt is then applied to the deck to help protect it from water and other elements. The new shingles are then installed on top of the underlayment or felt for a new roof that lasts for 20 years or more.
If the deck is severely damaged, it will need to be repaired to prevent further damage, which can eventually cause a hole underneath.
The process of removing the existing roof covering, repairing any damaged substrate and installing a new roof covering