What size nails do you use for a shingle roof?
How length is decided
Add up what the nail passes through at the nailing line: two laminated layers of the shingle being nailed, the top of the shingle below where courses overlap, the underlayment, and the deck. The nail has to clear all of that and either go 3/4 inch into the wood or come through the underside of a thinner deck. On 7/16 or 1/2 inch sheathing, a 1 inch nail can fall short at thick spots, which is why 1 1/4 inch is the common choice.
Typical lengths
- Field shingles, single layer, 7/16 to 1/2 inch deck. 1 1/4 inch.
- Thicker decks, 5/8 to 3/4 inch. 1 1/4 to 1 1/2 inch so the nail reaches 3/4 inch into the wood.
- Ridge and hip caps. 1 1/2 to 2 inches, since the nail passes through several layers of cap and shingle.
- Roof-overs. 1 3/4 inch or more to get through two layers, though tearing off is the better choice.
How many and where
The code calls for at least four nails per shingle unless the manufacturer specifies otherwise, and many manufacturers require six on steep slopes or to qualify for their highest wind coverage. Nails go in the manufacturer's nailing zone, driven flush, straight, and not near the shingle ends. Placement matters as much as size: a long nail in the wrong spot still lets a shingle blow off.
Compare shingle types in architectural vs 3-tab shingles, and see why stacking a second layer complicates nailing in roofing over existing shingles.