Improperly nailed roofs can be more susceptible to leaks and damage from storms. Ideal nail placement on roof shingles is limited to a very small area. If the nail is driven outside that area, it could impair the roof and void the manufacturer’s warranty. Contractors who hand nail can feel whether or not the nail catches the wood, but don’t get that same feeling with a nail gun. Hand nailing also ensures accurate placement of nail on designated nail line. Nail guns can drive nails between boards or outside the ideal placement area which will loosen over time, eventually causing raised shingles or leakage.