Roofing nails for typical asphalt/composite shingle installation should be corrosion-resistant (typically galvanized steel), have a minimum nomical shank diameter of 12 gauge (0.105″), and have a minimum head diameter of 3/8″. Roof decking or sheathing penetration should be at least 3/4″ (or 1/8″ past underside of deck) so 1″ or 1-1/4″ are the most commonly used roofing nail sizes for asphalt and fiberglass shingles.
What determines nail length is number of shingle layers, total shingle/flashing/underlayment system section thickness where being driven. Typically anywhere from 1-1/2 to 3 pounds of nails are required for each square.
The following is an approximation of how many nails it takes of a certain size to make up a pound: 2d=225ea/lb, 3d=190/ea/lb, 4d=165ea/lb, 5d=145ea/lb.Nails can be driven by hand or more efficiently with pneumatic nail guns.
Improper pneumatic or air adjustment or nail placement accuracy can lead to defects like sealing failures, raised tabs, and buckling.
The typical minimum number of nails required for each shingle is four, but this may vary based on manufacturer/product type. No nail head should be closer than 1″ from the edge of the shingle. Nails should not be driven into knotholes or cracks in the deck. Nails should be driven tight against the shingle but not overdriven or underdriven. If a heat-activated sealant strip exists on the shingles, nails may be driven through them so the sealer may later melt around the penetration and seal the hole/nail joint.