Believe it or not I used no roofing nails to put my roof on ,I used a staple gun....when I put my roof on I put three to four fasteners per shingle....depends on how your roof was made ...oriented strand board or 1x6 ...I would say 1 1/4" nails.....but when I did mine I took off all the old roofing materials(four layers)and then started with fresh drip edge/tar paper/rubber roof barrier for the edge of the roof line...and tar/seam sealer.....I would suggest watching a video either from expert village or this old house ...a picture(video) is worth a thousand words...later
How Many Roofing Tacks Do You Put Into A Three Shingle Roofing Tab When Reshingling A House?This Is A Second Layer Of Shingle.
You can put four roofing nails per shingle and use at least 1 1/2" nails. The second layer of shingles will last about 2/3's the amount of time of the shingle. For example, a 25 year shingle may last 15 to 18 years.