Thanks R. Adam, I'll try that hopefully it works well. Our house isn't that old but the streaks really make it look older.
R.Adam is correct, it is algae that is forming on the roof. Bleach can be used, carefully to spray on the roof and then wash it off, You just need to be careful as the roof when wet is slippery. Also you need to water down your grass and plants so not to get bleach on them. There are several home DIY use products for this as well that you can try. All require some sort of climbing and power washing.
To help prevent this from coming back or if you want to wait for a period of time. Metal zink strips placed under the top few rows of shingles with just about on or two inches showing to the weather will prevent this and will eventually remove the stains. The chemical action of the zink will bleed down onto the lower shingles every time it rains. Eventually creating an environment that is not conducive to this mold development.
Shingle manufactures removed this material in an effort to lower costs of roofing materials. However you still can purchase a higher grade shingle that has zink in the stone mix that protects the shingles from mold streaks such as these.
The photos below show a recent roof we power washed to remove excessive growth on the surface. Although we do not recommend such an aggressive cleaning method, we were successful in cleaning the roof and we expect to get at least another five or six years out of it before the owner will need to change it out.
I thank you for this info Woodbridge Environmental. That is a great explanation and advice. The zinc strips I will definitly install and since I do have a power washer I do believe I'll try the bleach method, that is with some help. I'm not quite as spry as I use to be now at sixty five but I can get some help. Thanks again for all the info.
There is a product called "Wet & Forget". Spray it on with a garden sprayer and you're done. The rain will take care of it. Moss, mold, mildew and algae all gone. Check out the website www.wetandforget.com
I buy it at Costco. I believe Ace Hardware also carries it.
You really shouldn't pressure wash your roof. Dangerous for one thing, and I'm pretty sure if your shingles are asphalt and you blow those little bits of gravel off you certainly will void your warranty.
Thanks Monica. I'm very careful when I do use my power washer because I've read enough things about people that haven't, lol. I'm going to check that site out and hopefully there's a store near me that carries it. Thanks again.