What is the best roofing nail length?

The rule behind the length

The International Residential Code requires shingle nails to penetrate 3/4 inch into the deck or through it, whichever is less. It also requires corrosion-resistant nails with at least a 12-gauge shank and a 3/8-inch head. To find the right length, add up what the nail passes through: the shingle at the nailing point (two laminated layers on architectural shingles, plus the course below), the underlayment, and the deck.

Common lengths and where they go

• 1 1/4 inch: field shingles on new roofs over 7/16-inch OSB or 1/2-inch plywood.
• 1 1/2 inch: 5/8-inch or thicker decking, and heavier premium shingles.
• 1 3/4 to 2 inches or longer: hip and ridge caps, especially over a ridge vent, where the nail passes through cap, vent and shingles. Vent makers specify their own minimum length.

Too short vs too long

Too short is the real danger: nails that barely grab the deck pull out in wind, and shingles blow off. A little extra length rarely hurts, though the points in the attic get longer. Follow the shingle wrapper and any vent instructions, since manufacturers can require more than code, particularly for high-wind installation.

Check before you buy

Measure the deck thickness at an edge or in the attic, read the shingle wrapper, and match the nail to your gun if using coil nails. For deck types, see OSB vs plywood roof decking, and for vent caps, see ridge vents vs box vents.