Those black streaks running down your roof dose not mean you need a new roof or that it is getting ready to fail, rather you have Algae on your roof.
this organism comes in either spores or clumps of cells on your roof top, if they are on the north side of your roof ,this area gets less sun and more moisture it is a great place for it to multiply and grow faster down your roof.
Asphalt shingles contain limestone, which makes them heavy, durable and reflective. Roof algae over time will consume the limestone and weakening the shingles.
Algae produce a dark pigment acting like sunscreen protecting the cells from the sun. As this algae accumulates on your roof shingles the roof becomes less reflective and causes your house to become hotter causing cooling bills to go up.
Roof algae is the first wave of attack on your roof, Algae eventually teams up with fungus to form Lichen. Moss follows next building layers of soil that catches seeds, bird droppings by the time grass is growing on your roof it’s time to get a new roof.
This algae has been around for 3 billion years. they were originators of oxygen in the atmosphere.
We have now learned how to properly remove this Algae and it’s friends before it ruins your roof, and save you money in the long run.