Surface residues or discoloring stains can affect virtually any type roof. One particular condition that has become more unremarkable in new geographic regions is discoloration of asphalt shingle roofing due to algae. Generally this condition only has an effect on a roof’s appearance, although, with certain roof products or the presence of other detrimental factors it may effect on the final service life of the roof.
The staining and staining due to algae initially appears as dark brown and black, or sometimes greenish streaks then spread across the roof surface. It’s most conspicuous on white or other light coloured roofs. This darkening is different from the blemishes due to mud and tree waste that tends to amass on localized areas of a roof ; but it’s not rare to find both conditions on some roofs.
Due to its appearance, the staining from algae is commonly known as "black mold" marking.
The algae growth has a tendency to occur most frequently on the northerly and eastern surfaces or where the roof is shaded or otherwise slow-drying after rains. The growths can be found in nearly all regions, although the problem is more extensive in regions where the weather is warm and damp at least part of the year. Extended hot, wet summer weather is a real contributory allow for allowing the algae to become well established. Cold, dry weather can slow or stop the spread but may not dump the condition altogether as the taints will remain.
Spores from the algae are carried by the wind. Once the algae gets started it will continue to spread, generally moving up and across the whole roof and at last throughout the neighborhood as spores. The successive growth of moss and other fungi that thrive on the algae and other organic matter that accumulates on the roof can heighten conditions.
Some techniques used to fight the algae are probably damaging to the roof and to the surrounding property. Aggressive washing ( e.g, by washing or high pressure spraying ) and the associated roof traffic may cause the loss of granules or other damage to the shingles leading to early roof failure.
There are commercially available treatments, as well as professionals that specialize in the work. Only cleaning solutions recommended by the roof manufacturer should be used. While some treatments will kill the algae right away, it might take one or two days or weeks for the colour to fade. Unfortunately, cleaning is only a short term benefit at best usually. If spores are there, the algae will begin to grow again almost straight away if the conducive leading to its growth first of all are still present.
To avoid injury or roof damage, it’s better to have the roof treated professionally. The cleaning solutions will make the roof surface slippery and dangerous. Before applying cleaning solutions, any dust buildup or waste should be carefully removed. Some cleaning solutions can kill grass and other vegetation, so run-off from the treatment process should be picked up or diverted to an appropriate drainage point. Foundation plantings should be covered and the applicator should wear protecting glasses, gloves and attire. It’s also crucial to wash the gutters and other surfaces with clear water to prevent the solution from corroding or staining them.
The most effective way to fight the marking and discoloration from algae is to prevent it from growing. Makers offer products with algae-inhibiting features. Labeled "algae resistant" ( AR ) or "fungi resistant," they have zinc granules integrated into the outer layer of the shingles next to the standard ceramic-coated granules to prevent the algae expansion on the granules. Copper or zinc strips placed at the ridge area of the roof can also control the growths. Installing a dark roof will not forestall the algae problem but it will be less obvious.