- Q. A roof I installedhas stains
running down the steel standing-seam roofing belowthe
skylights. What might be causing this and how can it be
prevented?
A.If the stains are rust trails,
they could be coming either from the cut edges of the
roofing or from the nails. More than likely it is from the
nails, so use stainless-steel nails or screws to secure the
flashing.
If the stains are dark, the corrosion is probably caused by
a galvanic reaction between the skylight flashing and steel
roofing panels. Some skylights come with pre-formed copper
flashings that will react with the cut edges of the steel
roofing panels in a relatively short amount of time. The stain
could also be coming from a reaction between the nails and the
flashing they are holding in place. To prevent problems, bend
your flashings from the same type of coil-stock as the
roofing.