Are roofing nails supposed to go through the roof deck?
Short answer. Yes. The International Residential Code requires asphalt shingle nails to penetrate at least 3/4 inch into the wood deck or all the way through it, whichever is less, and with common 7/16-inch OSB or 1/2-inch plywood that means the points poke through into the attic. Rows of nail tips seen from inside the attic are normal; nails showing through the shingle surface, or rusty, dripping tips, are not.
Why the nails go all the way through
A shingle nail holds by friction along its shank in the wood. Most roof decks are thinner than 3/4 inch, so to get full grip the nail has to pass completely through. The code also sets the nail itself: corrosion-resistant, with a shank of at least 12 gauge and a head of at least 3/8 inch.
What normal looks like from the attic
- Neat horizontal rows of nail points following the shingle courses.
- Points that are clean or lightly discolored.
- Denser nailing near the ridge and edges, where caps and starter strips are fastened.
What is not normal
- Rusty tips with drip stains or frost in winter: warm, moist house air is condensing on the cold nail points. That is an attic ventilation or air leakage problem, not a roof leak, but it can rot the deck over time.
- Water stains spreading from a nail line: water may be getting in through a nail hole or flashing above.
- Nails visible on top of the shingles: outside of the last ridge cap, exposed nails are an installation or nail pop problem.
- Nails that missed the deck: points sticking out beside a rafter or through a gap hold nothing.
A safety note
All those points are sharp. Wear a hat and move slowly when you work in the attic, and never stand where a ceiling joist is not under you. For why attics sweat, see roof ventilation basics, and for deck types, see OSB vs plywood roof decking.