Type of sealant for nails under asphalt shingles
I have used zinc make sure the strip extends beyond the shingles , we started using wide zinc strips at 2 levels after moving to Oregon and noticing no moss or fungus below the metal roof vents. I like black jack it is a good sealant and if putting a roof I accidentally have a shiner a dab of blackjack on top will seal that exposed nail head. Make sure to slip the zinc under on a warm day so you don’t break the shingles.