[ridpalcak]

when you look at one half of my asphalt roof you see rust stains approximately where the roofing tacks are. the other half of the roof no stains. what is the cause?

 

[AGWhitehouse]

water + metal = rust

Is that half in the shade allowing for higher moisture levels?

Are the fasteners exposed?

Do you live in a high wind zone where driving rains could get under shingles?