One of the questions I hear all the time during a New Jersey home inspection is, "John, should I be worried about those black streaks on my roof?"
Fortunately, the answer is usually no.
I've had buyers look at a roof covered with black streaks and immediately assume it needs to be replaced. Most of the time, that's simply not true. In fact, I've inspected plenty of roofs that looked terrible from the street because of black streaks, yet they still had years of service life remaining. I've also inspected roofs that looked almost new but had active leaks around a chimney or damaged flashing.
That's why I never judge a roof by its appearance alone.
Most of the time, those black streaks are caused by a naturally occurring airborne algae called Gloeocapsa magma. The algae settle on asphalt shingles and grow where the roof stays damp the longest. That's why you'll usually see the streaks on the north side of the house or beneath large shade trees where the sun doesn't dry the roof as quickly.
The black streaks themselves usually aren't the problem.
What interests me is why they're there.
When I see black streaks during a NJ home inspection, I start looking at the conditions that allowed them to develop. Is the roof heavily shaded? Are tree branches hanging over the roof? Are the gutters clogged or overflowing? Is the roof holding moisture longer than it should? Is moss beginning to develop? How old are the shingles?
Those answers tell me much more about the condition of the roof than the black streaks ever will.
One mistake I see buyers make is assuming that anything ugly must be expensive.
That's rarely the case.
Black streaks are usually cosmetic. Missing shingles, deteriorated flashing, soft roof decking, exposed fasteners, or evidence that water has entered the home concern me much more than algae staining. Those are the conditions that can shorten the life of a roof and lead to costly repairs.
Another question I hear is whether the roof should be pressure washed.
My answer is almost always no.
Pressure washing can remove the protective mineral granules from asphalt shingles. Once those granules are gone, they don't come back, and the life of the roof may be shortened. If you want the roof cleaned because the appearance bothers you, hire a contractor who specializes in cleaning asphalt roofs using low-pressure methods designed specifically for roofing materials.
If the black growth turns out to be moss instead of algae, that's a different situation. Moss holds moisture against the shingles, can lift their edges, and may shorten the life of the roof if it's allowed to spread. It's much easier to remove moss while it's still a small problem than after it has covered a large section of the roof.
People also ask me if black streaks affect homeowners insurance.
By themselves, they usually do not. Insurance companies are generally much more interested in the overall condition and age of the roof than cosmetic staining. A roof that's structurally sound and doing its job is far more important than one that's perfectly clean.
During every home inspection, I'm evaluating the entire roofing system, not just what catches your eye. I'm looking at the shingles, flashing, roof penetrations, gutters, drainage, attic ventilation, visible roof structure, and any signs that moisture has found its way into the home. Black streaks are simply one piece of the puzzle.
If you're buying a home, don't assume black streaks mean you need a new roof.
Have the roof evaluated during a professional New Jersey home inspection by an experienced NJ home inspector. Experienced NJ home inspectors know the difference between a cosmetic condition and a defect that could cost you thousands of dollars after you move in.
After performing more than 8,000 NJ home inspections, one lesson has stayed with me.
The things buyers notice first are often cosmetic.
The things that end up costing the most money usually aren't nearly as obvious.
That's why hiring an experienced New Jersey home inspector is about much more than getting a report. It's about understanding what the house is trying to tell you before you own it.
Sometimes black streaks are nothing more than algae.
Sometimes they're one small clue that's part of a much bigger story.
A good home inspector knows the difference, and that's exactly what a thorough home inspection is designed to uncover.
John Martino is a Board-Certified Master Inspector and owner of LookSmart Home Inspections in East Hanover, New Jersey. Since 2002, he has performed more than 8,000 New Jersey home inspections, helping home buyers understand the true condition of a property before they purchase it. His articles are based on real inspections, real client questions, and over two decades of experience evaluating homes throughout New Jersey.
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