Where the old covering is completely removed, the roof deck should be made smooth and solid and swept clean of all loose material, especially nails or other objects that might puncture the new roofing.
If the sheathing is wood, boards, should be uniform in thickness, well-seasoned, dry, free from cracks and knotholes, and securely nailed in place.
Tongued-and-grooved boards are preferable, but square-cut boards are satisfactory, provided they are laid close together.
Defects in the sheathing, including knotholes, should be covered with tin nailed around the edges. If the deck is not laid tight, wood strips of the same thickness as the existing sheathing should be inserted to fill in the spaces. After the roof deck has been properly conditioned, asphalt shingles should be applied in accordance with the manufacturer’s directions.