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What Are Those Black Streaks On My Roof?

If you have an older house (or at least an older roof), you probably noticed some black streaks over time, or noticed them on more visible roofs around you. You’ve invariably wondered what causes this, and suspected age or decay of the roof materials. This isn’t the case. These black streaks can be caused by a couple things, though one of the two is far more common (and fortunately easier to remedy).

You know that your roof is important, and while these are more cosmetic than anything else (aside from extreme cases), your roof needs to look good. It directly impacts your curb appeal, which can make or break your relationship with your neighbors and other members of your community. This also reflects on who you are, as your house speaks literal volumes about you.

It also affects resale value, even if it’s just a quickly-solved cosmetic problem. And truth be told, while this isn’t lasting damage, if it’s left unattended, it could begin to decay the materials, and promote water damage and reduced durability. It’s not good for your shingles, it looks bad, and one of the two problems is a sign of bigger problems which aren’t good.

So, what are these two problems? The more common one, we’re going to discuss at further length, so let’s get the simpler (but also more serious) one out of the way first. Some of this is the result of soot or other deposits. These are actually a big problem, because these deposits are very acidic, causing your roof to decay rapidly. It also means that you’ve got a less-than-sealed chimney or other type of vent that lets smoke and fumes out.
If it’s soot/smoke deposits, you need to remedy this immediately. However, these tend to be more understated, shorter streaks. If you have long ones that look like rivers or streams, chances are that these are algae colonies.

You read that right – algae. We think of this as something only living in bodies of water, but you may notice that puddles and ponds will grow algae without any other water source feeding them. It seems like algae just spawns by magic. The truth is, algae spores float in the air, and will grow on anything if they have the water supply and base nutrients. Shingles and other roofing materials like it are prime real estate for algae colonies, second only to inhabited water supplies and other plant life they can parasitize.

These colonies won’t immediately destroy your roof, but they produce some of the acidic compounds that makes soot bad for your roof, and the stuff is unsightly. Over time, it can permanently stain, or attract other things that’ll eat at your roof too.

But don’t panic! If these are a recent development, or a perennial one, there are ways to handle the problem. However, if you try too extreme or less than ideal approaches to this, you will do worse damage most likely.
We’d like to take a moment to discuss what to do about this.

Disposing of Algae Stains

First of all, this should be handled by a professional, plain and simple. It doesn’t matter how handy you are, you need an insured professional to do this. It’s dangerous for a lot of reasons. However, we’ll talk about the proper solutions to this, so you know you have a competent professional by the approach they intend to employ.

The use of copper and zinc is probably key, because these organic metals are quite toxic to algae, and are active ingredients in algicides used for fish tanks and ponds. Following this, the use of a hose with decent water pressure to remove the dead algae is pretty straightforward.

Preventing Algae

This is done with treatments that are a preventative version of the above, using compounds toxic and inhospitable to algae colonies. You can’t prevent algae itself, the air is full of it in most parts of the world, even in deserts if you can believe it.

Keeping your roof clean, and preventing too much shade or branches hanging over it goes a long way, as while algae does need sunlight, they also need a fairly damp, partially-shady location that’s not too hot as well. Given that algae is at its worst in the spring and summer, when the sun is also out in force in most places, the hot, shade-free regions of your roof are less likely to get particularly nasty colonies.

This does not completely prevent them, nor do algicide treatments. There has yet to be a technology nor natural force that can make a home completely algae-proof, but the more effort you put into abating it, the less cleanup you will face, and vis a vis, the less it will cost when you do inevitably need to clean algae colonies off your roof.

J&M Roofing

At J&M Roofing, we have decades of experience maintaining, cleaning, repairing and installing every kind of roof you can name. Is your roof looking dirty? We can clean it. Looking spotty? We can repair it. Looking completely worn down? We can replace it. Fill out our contact form today for a zero obligation estimate!

Ready to get started?

Our contractors have the knowledge and experience to handle any roofing project, no matter the size and scope. Call us today to schedule a free consultation with one of our experts.

We’ll begin by assessing the current condition of your roof and will develop the best plan based on your circumstances. We can help you decide if repairs will be an adequate fix or if it’s a better investment to re-roof.

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