Why Clean the Roof?

Most folks probably don’t spend much time thinking about the cleanliness of their roof. If it’s not leaking then there’s not a problem, right? Wrong. There are a number of roof cleaning issues that if left unchecked, can wreak havoc on shingles, shakes, and tiles, eventually leading to deterioration of the roof structure itself. This article will discuss some of the signs of trouble, the causes, and some of the cleaning methods used to eliminate potential problems. Preventative measures are always less expensive than repair or replacement costs.

Black Algae – Often misnamed ‘mildew’ or ‘fungus’, black algae is usually found on the shadier slope of the roof, or on an area shaded by a tree. The staining tends to be uniform, unlike the black streaking seen when asphalt shingles bleed-through. The black stain is actually dead organic debris from dead algae. There are shingles made with zinc or copper granules designed to inhibit algal growth. Another way to help avoid black algae is to trim tree branches overhanging the affected area, allowing more sunlight. There are also zinc or copper strips that can be tacked to the ridge that will cause algae- killing metal salts to wash down the roof when it rains. Some people pressure-wash the algae, but I feel this is detrimental to shingle integrity. There are plenty of chemical solutions to remedy this problem. It is best to contact a professional roofing contractor to help make the right choice, both for you and your roof type.

Debris Staining – Is a fairly common problem, especially on low pitched roofs with overhanging branches. Staining occurs when piles of debris, such as leaves or needles from coniferous trees collect on the roof. These piles retain water and can cause serious damage if not dealt with. Not only can algae and fungus originate here, but also actual plants. I have seen roofs with 6+ ft. plants growing on them, complete with elaborate (and destructive) root systems growing into the roof structure. Moss, lichens, and other plant life can often thrive on a neglected roof. The main way to combat this particular type of problem is to physically remove debris from the roof by sweeping and/or washing plant matter from the roof. Care should be taken not to damage any shingles or other roofing material. Debris staining is a prime of example of how prevention can be far less expensive than repairs. It is far easier to remove debris from a roof than to fix the resultant damage if not removed.

Black Streaking – When black stains occur on your roof in the form of streaks, it is most likely a case of ‘bleed through’. This occurs when the bituminous material in asphalt shingles begins to break down and bleed from the shingle. Unfortunately this is usually a sign of faulty materials, or older shingles in need of replacement. It can be hard to distinguish bleed-through from black algae, which is why I always recommend seeking the advice of a trusted roofing contractor before making any decisions on course of action.
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