Owners of homes with metal roofs have sometimes reported dark streaks occurring on their eave fascia boards after the roof is installed.
Although some homeowners worry that the streaks might be from paint washing off of the roofing, they can rest assured that this is definitely not the case with metal roof systems that have high quality paint systems, such as the Kynar/Hylar systems. This streaking problem occurs almost exclusively in climates where large amounts of airborne fungus exist. Because metal roofing will not hold or support fungus that lands on it, this fungus washes off of the roof and runs down the fascia boards, causing streaks. Heavily profiled metal roofs typically channel the water in certain areas and this can be seen in the streaking. In essence, rather than streaking the roof like it does with conventional roofing, fungus is washing off of the roof and streaking the fascia.
If gutters are installed on the building, this streaking will not be visible. If, for whatever reason, gutters are not to be installed, there are several things that can be done to help minimize this problem. In some cases, the drip edge from the roofing can be adjusted to help direct fungus-laden water away from the fascia. However, some will always blow back against the fascia. Using a paint for the fascia with a fungus-inhibitor in it can help. Also, installing metal fascia, particularly those produced from Kynar/Hylar coated metal, can help in resisting streaks. Another option is to use dark-colored fascia to help mask the streaking. Also, if desired, there are readily available cleaners that can be used to periodically clean streaks from the fascia.