The length of each nail must be a minimum of 1 inches long and for roof overs atlas recommends a nail length of at least 2 inches.
Roofing nail length second layer.
To determine the nail length you should consider the number of layers of shingles shingle thicknesses underlayment and flashings installed on eaves.
Nails of the proper length should penetrate three fourths of an inch into the roof deck.
If your decking is less than 3 4 inch then a 1 1 2 inch nail will suffice.
If you are putting a layer of asphalt shingles over an existing layer of asphalt shingles on to a 3 4 inch deck or a plank deck then you should be using 1 1 2 inch nails.
Roofing nails should be long enough to penetrate the roofing material and go 19 mm into osb solid wood plywood or non veneer wood decking or through thickness of decking whichever is less.
Place the top of each starter shingle firmly against the bottom of the shingle immediately above it and even with the eaves then nail it into place.
Select a length of roofing nails that penetrates completely through the new layer of shingles existing layer and the wood roof deck.
However where the roof deck is less than three fourths of an inch thick the nail should be long enough to penetrate fully and extend at least one eighth of an inch through the roof deck.
Use 1 5 or 1 75 inch roofing nails.
Use galvanized roofing nails long enough to fully penetrate the sheathing typically 1 1 2 inches for a second roof and 1 3 4 inches for a third.
Apply the shingles to all roof planes ending a row of shingles at the top of the plane which is the ridge or peak and cut to follow the profile of any outside corners.
How to shingle over existing shingles and how to shingle a roof how to install roof shingles shingle layout lines h.
Wood shakes minimum 3 4 sheathing wood shakes nail type minimum length 18 straight split 5d box 1 3 4 18 and 24 handsplit and resawn 6d box 2.
Flashings for re roofing asphalt shingles.