Jump to content

Black Streaking on Roofs


Terence McCann
 Share

Recommended Posts

The black streaks are most likely a fungal growth, much like the algae and/or lichens on the left side of the roof in the photo. At various seminars, the experts--alleged, anyway--claim that the growth is caused by vegetation blocking the sun and/or the house's position vis a vis the sun.

Link to comment
Share on other sites

Hi,

Yeah, it's algae. Folks often mistake it for dirt, weathering or smoke. There's no alleging to it. It's a fact. It eventually develops on the north and east sides of every roof here, unless special shingles that have copper included in the granular coating are used. It also develops on the sunny south and west sides in any areas shaded by trees or chimneys or adjacent roof planes or houses.

Algae secretes oxalic acid. Leave it there long enough and it can actually harm an asphalt roof. I've had roofs where the south slope, where the sun hits it, is clean, algae free and nice and supple and the north slope, where the algae stains are, will show more wear and be brittle and nearly crystalized. Same product, installed at the same time on the same house, but with very different conditions of serviceability. I always get a chuckle out of all of the home inspection texts that show the south slope of roofs being the one that will wear out first due to sunlight exposure. That might be true in other parts of the country but not here. Here it's almost always the north or east side or areas in the shade and the sunny sides, where the sunlight kills the algae, can look great at 20 years while the north sides look like they've been on 30.

It's easily removed with a mixture of gallon of liquid sodium hypochlorite (swimming pool chlorine) 3-1/2 gallons of water and a pint of non-ammoniated liquid dishwashing detergent. Wet down and cover plants and grass beneath the eaves to protect them from the overspray, mist the roof with a garden hose, apply the solution working from the eaves to the ridge, allow it to work and then rinse it off with low pressure water.

ONE TEAM - ONE FIGHT!!!

Mike

Link to comment
Share on other sites

Hi,

Sure, if you want to install them every 3ft. or so about every 10 or courses. After about 3ft. they aren't very effective. The homeowners put them on themselves around here. They invariably leak around the nails used to secure them to the roof because they don't bother to seal them or place them under an overlapping shingle and the danged things get hooked by the wind, break off and then look like hell.

OT - OF!!!

M.

Link to comment
Share on other sites

Terry,

What age was the roof?

Unlike Mike, I've never seen algae actually damage a shingle here in MA, where the climate is similar to yours. Algae is an aesthetic concern only around here.

But zinc, copper, and lead strips are all fungicides and will clear part of the roof if that's what your clients want.

Good Luck,

Link to comment
Share on other sites

This algae came on the scene here in Richmond only within the last 8 - 10 years. It used to be a far South phenomonon so I'm told.

I did a home inspection for a client whose dad told me that his new roof was made to resist this algae and has for several years. Has anyone heard of such a shingle?

Link to comment
Share on other sites

Hi,

Yes. I mentioned them in my post above. Google "Gloeocapsa magma" and you'll find out all you'd ever want to know about roof algae. Just about every manufacturer of algae-resistant shingles will show up during that search.

Better yet, here, I've done it for you: http://www.google.com/search?sourceid=n ... apsa+magma

OT - OF!!!

M.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...