The Sun Is Shining, and My Roof Is Dirty. Ugh.
It's a lovely day and everyone is out tending their gardens and cleaning their cars, but what about cleaning the roof? As I drive down the street I absentmindedly note every single roof that needs attention. I can't help it - when I see a stained roof, I think: "Such a shame, the house looks so lovely, why won't they pay attention to their roof, too?"
See the roof above? That's what I see the most of in my neighborhood. The culprit is a form of mold; like mildew. It stains in streaks, and will attack even mold-resistant shingles if the right factors are involved.
Before we talk about how to clean it, let's get right down to why it happens.
Similar to the ice dam, roof mold starts with a roof that is not performing up to its full potential. Attic ventilation is poor, there are great temperature variations in the surface, and this allows for dew to form on the shingles during damp seasons as well as during the summer. The mold loves standing water! First the water allows the spores to adhere to the roof, and then it feeds the spores so that they hatch and create more spores, slowly working their way down your roof.
Cleaning treats the symptoms, but adequate ventilation cures the disease. Check your soffits (the underside edge of your roof) for vents and make sure that (in a bad case of mold) that you have at least one vent per every six feet, or even better, one vent for every three feet. This will allow air into your attic. Next, make sure that your ridge vent is at least running 3/4 of the length of your roof. See the picture above? They have good ridge venting, but they have virtually no soffit vents. The little eaves vent pictured above will never make up for having no soffit vents. Failing this, a fan might be installed to get the air moving. That's the key.
Let's move on to cleaning: this can be done mechanically and chemically. One doesn't have to have a power-washer as strong as the one pictured below:
This pressure washer is great, but watch that PSI. Too strong a jet will blast the granules (the sandy stuff) right off your roof, and you don't want that. The granules contain the pigment that colors your roof, but nowadays also contain little bits of reflective material that reflects the sun away from your house on very sunny days. So even if you have a dark roof, those reflective granules are still working hard to keep your roof cool.
Simpler and more gentle solutions look like this:
The application of cleaning fluids washes the roof, rather than blasting it. Using the right chemicals, your roofer will first "soap it up", and then "rinse it off", and once the mold has been washed away, he will apply a mold-resistant seal that will retard further growth.
It's really up to you as to whether or not to ventilate your roof correctly, but a good roofer will always recommend a prevention with proper vents. He's not trying to get you to spend more money, he's trying to help you so that you will not have to do the same thing next year!
Before we talk about how to clean it, let's get right down to why it happens.
Similar to the ice dam, roof mold starts with a roof that is not performing up to its full potential. Attic ventilation is poor, there are great temperature variations in the surface, and this allows for dew to form on the shingles during damp seasons as well as during the summer. The mold loves standing water! First the water allows the spores to adhere to the roof, and then it feeds the spores so that they hatch and create more spores, slowly working their way down your roof.
Cleaning treats the symptoms, but adequate ventilation cures the disease. Check your soffits (the underside edge of your roof) for vents and make sure that (in a bad case of mold) that you have at least one vent per every six feet, or even better, one vent for every three feet. This will allow air into your attic. Next, make sure that your ridge vent is at least running 3/4 of the length of your roof. See the picture above? They have good ridge venting, but they have virtually no soffit vents. The little eaves vent pictured above will never make up for having no soffit vents. Failing this, a fan might be installed to get the air moving. That's the key.
Let's move on to cleaning: this can be done mechanically and chemically. One doesn't have to have a power-washer as strong as the one pictured below:
Simpler and more gentle solutions look like this:
It's really up to you as to whether or not to ventilate your roof correctly, but a good roofer will always recommend a prevention with proper vents. He's not trying to get you to spend more money, he's trying to help you so that you will not have to do the same thing next year!
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