This suburban migration may not seem to have anything to do with stained roofs, but it provides a 45 year history of a single home’s roof. My parents’ home never had a problem with roof stains until around 2005. I know growing up here I never saw it, but now you see it everywhere. The question is what changed over that time period to allow the staining, and, as important, what causes roof stains and what do we do about them?

Algae Stained Roof
I’ve heard some very interesting speculation regarding the cause of these stains, everything from tar seeping from the shingles to jet fuel dumped from airplanes. The answer is surprising but pretty simple. The black streaks that we see on roofs are actually algae growth. This algae, Gloeocapsa Magma begins its life opaque or green but as the colony grows and ages it produces the classic black outer shell to protect itself from the sun’s ultraviolet rays. We also see lichen and moss, two other types of growth on roofs that accompany the algae.

Lichen looks like barnacles and range in size from a dime to a silver dollar and lives symbiotically with the algae. Moss looks like green fuzz and ranges from 1 inch to 6 inches in diameter. Lichen and moss both live off of, and with, the algae.

When looking at the life cycle of algae, we see it grows from spores produced by mature colonies. The spores are dispersed by the wind and living carriers like birds and squirrels. Whether or not they grow requires a few conditions, but most important are moisture and a food source.

The moisture required for growth comes from our humid environment; daily from dew and occasionally from rain. It grows in the places that stay moist the longest. These are the north or west side of the roof or areas where trees or parts of the structure block the sun. The old adage about moss growing on the north side of the tree is in a way true. This is due to the sun’s position in the sky which creates shade on the north side for much of the day.

The lack of sunlight means that rain and dew evaporate from these areas last and they stay wet the longest. In fact, the classic streaking is caused by gravity pulling the moisture down the roof; the colony grows with the flow of moisture following the path of least resistance.

Now we have the spores and the moisture, which brings us to the food source and my parents’ house. What changed there since the mid-sixties? The only fundamental change was new roof shingles, first around 1980 and again in 2000.

Why now?
In the late 1980’s shingle manufacturers changed the composition of asphalt roof shingles. The new composition removed a good amount of the asphalt to increase fire retardant ability and to lower production costs. This new formulation required a filler to maintain the shingles’ weight to prevent wind damage. The filler that is used is crushed limestone. More specifically, it is the calcium carbonate that makes up the limestone that is the food source for roof algae.

So when my parents said, we’ve never had this problem before, I explained it was the shingles that had changed.

Climate Change?
Now there may be another factor at play here. I certainly don’t intend to start a debate on global warming, but climate may be playing a role too. The problems we see with roof algae first began in the south, where temperatures are not cold enough to kill off the algae during the mild winters. The problem seems to have crept north from there.

Typical Lichen Growth
According to the Arbor Day Foundation our area has seen a change in its ‘Hardiness Zone’. Hardiness Zones are geographic areas where certain plants will grow in the lowest average winter temperature. Based on temperature measurements from 1990 to 2006, the zones have crept north and our area was changed in 2006 from zone 6 to zone 7. It is possible that not having low enough cold temperatures could contribute to this continued growth.

So what damage can this growth do? The first is aesthetic. The stains are unsightly and look filthy, they detract from a property’s beauty and the property’s value. The physical damage is caused by the retention of moisture on the roof by the algae, which can make premature roof replacement necessary. The lichen and moss both eat away at the shingle, and the lichen can root through the shingle creating a path for water to follow into the structure.

How do we get rid of it?
How do we get rid of this growth and the stains? When determining the best method of stain removal the most important step is to look at what NOT to do. Never let anyone on your roof with a pressure washer. This will remove granule from the shingles and shorten the life of the roof. In addition to pressure washing, avoid any type of agitation. Scrubbing of any kind will damage the roof.

There are many products, techniques and methods out there. Some of these products clean and some attempt prevention. We need to separate the two for a clearer view of them. Let’s look at cleaning methods first.
By far the vast majority of professional roof cleaning companies follow the guidelines provided by the Asphalt Roofing Manufacturers Association (ARMA). The cleaning formula they recommend to the general public is store bought bleach, water and trisodium phosphate applied with a garden type pump up sprayer. This method will work, but it will take many applications and the limited capacity of the sprayer will make each application very time consuming.
Professional roof cleaning companies just use stronger types of bleach, classified as liquid chlorine, which is also known as sodium hypochlorite. They apply it with small electric or compressed air powered pumps that have a greater capacity to cover a large area quickly. These pumps are similar to those used by landscapers who spray liquid fertilizer on your lawn.

The formula provided to the general public is watered down to make it safe for a non-professional to use. It’s no different than fertilizers and pesticides you can purchase at Home Depot or Lowes, which are many times less the strength of the contractor grade products professional landscapers use on your lawn. As a professional New Jersey pressure washing company, we know the proper precautions to take and have the experience to ensure safe and effective use of these stronger formulations. A professional New Jersey roof cleaning will prevent new growth for 2-5 years and any professional roof cleaner will offer at least a 2 year warranty.

Almost every other New Jersey roof cleaning method requires the use of a pressure washer or some form of agitation and they are not recommended by the ARMA. There are some companies out there that use sodium hydroxide or caustic soda, more commonly known as lye. Sodium hydroxide is also the main active ingredient in many drain cleaning products. If you’ve ever used a drain cleaner you know the precautions you must take to use even a very small amount in your drain.

This caustic is also a very strong degreaser used for cleaning oil from concrete. After application it must be sprayed off with a pressure washer. Like the use of a pressure washer, the use of a degreaser on asphalt shingles, which are a petroleum based product, is not recommended.

Most of the consumer grade products are oxygenated bleach or sodium percarbonate. They are the same as Oxyclean™ type products with less filler added. Again, after application they require the use of a pressure washer to complete removing the stains. These are usually advertised as deck and New Jersey roof cleaners.

Any process that requires a piece of equipment or any apparatus to be placed on the roof is never recommended. These pieces of equipment displace shingle granule not only by spraying chemicals and water but also simply by their own weight and the wheels running up and down the roof.

Can we prevent it?
In addition to the most common New Jersey roof cleaning methods, there are also many methods of prevention. Unfortunately, there is currently no magic bullet. One of the most commonly discussed methods are strips of zinc or copper. These are placed along the ridge of the roof under the first row of shingles with a few inches exposed. The few exposed inches are sacrificial and oxidize as they weather, creating copper or zinc oxide. These prevent algae growth, but will not kill existing growth. The problem with this application is there just isn’t enough zinc or copper exposed to provide coverage for the entire roof. The area 3-5 feet below the strips will be free of growth but growth will occur lower on the roof.

Roofing manufacturers offer algae resistant shingles. They work in the same manner as the strips but have zinc or copper bits mixed in with the granule on each shingle. They are relatively effective but the longest warranty is only 10 years. The roof may have a 25 year warranty but the algae resistant properties are only covered for the first 10 years. These shingles are sold at a premium over the price of standard shingles and the warranties generally begin to prorate after the first year.

There is a company that provides the application of an EPA approved algaecide. They offer a 2 year warranty. The product does not clean the roof but is applied after the roof is cleaned. The company offers a maintenance plan to reapply every few years.

We now know what the stains are and their cause, how to get rid of them and how to attempt prevention. If I didn’t know better, I might have guessed that, like my parents over 40 years ago, algae too had joined in the great migration to the suburbs. If that were the case, I couldn’t blame them, my parents made a great choice moving us here!

Article Author: John Doherty of Garden State House Wash & Roof Cleaning, www.gardenstatehousewash.com

Published in Community Trends magazine. Community Trends magazine is a monthly for the CAI-NJ. They represent homeowners associations and property management companies.