Shingles are the first barrier against external environment and often the one that gets the most credit for preventing leaks and structural damage, but they're just one of the layers keep your shelter dry. The leak barrier protection creates a seal to prevent water from penetrating vulnerable areas. The synthetic roof deck protection provides the second layer of defense against roof rot. Ventilation, believe it or not, plays an essential role in maintaining the health of your shingles (and your own especially if you saw the energy bill of a poorly ventilated roof). We recommend to replace the entire roofing system when you do any reroofing.