Should roofing nails go through the sheathing?
What the code says
The International Residential Code's asphalt shingle fastener section requires corrosion-resistant roofing nails with at least a 12-gauge shank and a 3/8 inch head, long enough to penetrate at least 3/4 inch into the sheathing, or through the sheathing when it is less than 3/4 inch thick. With typical 7/16 inch OSB or 1/2 inch plywood, the nail must go all the way through.
Why full penetration matters
Holding power comes from the length of shank gripping wood. A nail that stops partway into a thin panel has very little grip, and shingles nailed that way are more likely to lift in wind. Shingle manufacturers' instructions say the same thing in their fastener requirements.
Nail tips in the attic
- Normal: rows of nail points along the underside of the deck.
- Frost or droplets on nail tips on cold mornings means warm, moist air is condensing on the metal. That points to ventilation or air sealing problems, not a nailing problem.
- Rusty tips and stained wood around them are a sign that condensation has been happening for a while. See roof ventilation basics.
Exceptions to plan for
- Exposed overhangs and porch ceilings where tips would show, so installers plan fastener length and placement there.
- Ridge caps over ridge vents, which need longer nails to reach through the vent into the deck.
- Thicker decks, where 3/4 inch penetration is the requirement instead.
Nailing quality is one of the biggest factors in wind resistance, as covered in wind damage to roofs in Georgia.