Roof Cleaning: Nothing But The Facts Please (Part One)

Roof cleaning is becoming more and more popular especially in the Southeastern United States because of an airborne algae called “Gloeocapsa Magma”. It is identified by the black streaks and stains that are mainly found on the north facing side of the roof, but does spread to the entire roof eventually.

For Gloeocapsa Magma to grow, it has to have heat, moisture and a food source. The heat and moisture source is easily provided by the warm and humid Southeastern climate. The food source is mainly provided from limestone fillers found in asphalt shingles.

 Limestone was introduced to the shingle manufacturing process when oil prices started to escalate some years ago. Asphalt impregnated material was used in the shingles to add weight and substance to the shingle. To save on rising petroleum cost, and ultimately shingle costs, the manufactures substituted limestone in place of some of the asphalt material.  Limestone being relatively cheap and dense was an ideal substitute. However, limestone also feeds Gloeocapsa Magma. Feeding off of the warm temperatures, high humidity and limestone in the shingles for food, if left unattended, the algae can cause some significant damage over time. 

In the beginning this algae is more of an eyesore than anything, and can be easily removed. Left on the roof, it will keep spreading until it covers the entire roof. At this point it becomes food for mildew and lichens and this is where the real trouble starts. Be careful! Many times a roofer will be called in to inspect the roof and some roofers will tell the homeowner that they need a new roof and in some cases, that may be so. But, too many times just a cleaning will suffice saving the homeowner thousands of dollars.

However, left unattended, the mildew will build up over time until there is a substantial layer of which can breed mildew. The mildew builds up to a point that moss will begin to grow. Moss can the lead to Lichens and Lichens have little tentacles that grow down into the shingle. Once the tentacles get established, they are very hard to remove and in the process, some of the shingle grit will be dislodged leaving pits or holes in the shingles.

So it is recommended to remove the stains before it gets that bad. The best time to clean the roof is in the warmer months and when the algae covers 30% to 40% of the north roof. By this time it is likely that is has spread to other areas of the roof and will only be a matter of time before it begins to show. The longer you wait, the harder and more costly to remove.

Now the question becomes, how do you remove it. In part two we will discuss the two most popular removal techniques, and the right removal technique.

Douglas Johnson
Taskmasters Wood Maintenance

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