I've had the opportunity to speak with many homeowners and property managers that are plagued by the problem of unsightly black streaks on their roof.
What are these streaks?
How are they caused?
How is it cured?
This post is dedicated to answering these three questions and giving you the information you need to keep your roof clean and beautiful.
So what are these black streaks and how are they caused? They are blue-green algae that is found in the lakes, rivers and ponds around the country. Blue-green algae is a known health hazard shutting down our leisure water areas. Birds, squirrels, wind and several other factors carry this algae onto roofs. The algae embeds itself and creates it own sunscreen by turning black. You may have noticed (if you've been around a while) that this problem has exploded in the last 30 years. This transition started when shingle manufacturers changed the base sheet of asphalt shingles from asbestos to organic and fiberglass mats and started using crushed limestone as filler. This crushed limestone is food and shelter for blue-green algae.
So how is it cured? By killing the blue-green algae. There are three prominent ways to accomplish this task. Chemical treatments like bleach and TSP will temporarily eliminate the pest. Metal strips on the roof will create a metal oxide wash when it rains that kills the algae. Shingles manufactured with metal in the granules will also create this metal oxide wash when it rains to kill the algae. So here are your 3 solutions.
1: You may clean your roof by climbing up there and spraying it down with a mixture of water, bleach and TSP. Let it sit for twenty minutes and then climb up again to rinse it off with a hose. This method has been controversial because bleach and TSP do not penetrate the shingles to kill the embedded algae causing the stains to return within a year, it dries out the shingles and lead to curling and foot traffic on the roof will dramatically shorten the life of your roofing system. There are other cleaners available, but they too will require periodic treatments and foot traffic on the roof.
2: Put zinc or copper strips on the roof. These unsightly strips release the metal oxide wash that will prevent blue-green algae from developing.
3: Put algae resistant shingles on your roof when you have it replaced. Most shingle manufacturers now make an algae resistant shingle. They have some copper in each granule so that the metal oxide wash that kills blue-green algae is released when it rains on your roof. Most manufacturers give a ten year warranty that prorates from day one on black streaks from algae growth. In the fine print, these warranties state that the manufacturer is on the hook for one cleaning and then the warranty is fulfilled and no further coverage is offered. So if your cleaning is in year 3, you will have no warranty.
The best solution I have found is 3M scotchgard on shingles. These shingles have 7-10 times as much copper as the competition and offer a lifetime residential (20yr commercial) non-prorated warranty on black streaks from blue green algae. In Central Ohio, Atlas is the only manufacturer that offers 3M Scotchgard shingles. These are the Pinnacle Pristine and StormMaster series.
Visit Preferred Building Services of Ohio to learn more about the advantages and cost of solving this problem on your home.