If you own your home, and keep it long enough, eventually you will have the pleasure of replacing the roofing. This is a major expense, but roofs can last from 15 to 30 years depending on the shingle quality and your environment.

We (read that my spouse) put a new roof on our starter home. He and a carpenter buddy did the work themselves. It was over 40 years old at the time and had two layers of shingles on it.

We had our current home re-roofed when it was only 13 years old. The ‘new’ roof has now been in place for 16. About 2 years ago, the north facing slope (shaded by big trees) started streaking black in the small dips between the beams. I thought we might need to think about putting on another new roof and made some budget adjustments to plan for that.

In my bathroom shower, for years, I have been spraying the base of the tiles (at the bottom) with a bleach/cleanser solution after cleaning the tiles and shower basin. It keeps the mold and mildew from growing. As I walked past our north facing roof every day on my walks, it occurred to me that I should try a similar solution to the roof. I pondered that thought (I was afraid the bleach would damage the shingles or discolor them horribly) for several months when out of the blue, my spouse wondered aloud if bleach would clean up the black streaks.

Since we are starting to think about selling and moving to a less developed area, I decided to do a bit of research on the idea in hopes of avoiding a major roof expense in the next few years.

Here is what I found and did for less than $50 to refresh the look of that roof.

Your roof can be a host.

Things grow on your roof. If you have ever been to the northwest states (think Washington), you probably noticed houses with green roofs. We visited Olympic National Park in 2009 and noticed that the reproduction cabins (shingled with wood shingles) had roofs that were just covered with moss.

But it isn’t just the northwestern states that have to worry. Where ever there are warm moist summers, your roof can grow algae. This is what was on our roof. It was really ugly and I knew that any prospective buyer would immediately think – aha! new roof needed.

What is algae and what does it do to your roof?

What I found is that the black streaks were caused by algae named Gloecapsa Magma. The spores are air borne and require shade and moisture to get established. They feed on the limestone (calcium carbonate) in asphalt shingles. My algae diagnosis was borne out by noting that the places where there were no black streaks were directly under some sort of metal object. The runoff from the metal is lethal to the algae, keeping it from attaching to the roof.

Algae, some references claim, is just an unsightly cosmetic issue. However, when I looked closely at our shingles, I noted that there were tiny bits of moss starting to grow – but only in the areas with the algae. Most sources agree that moss will eventually damage your shingles because the roots grow into them.

Algae also can cause your shingles to hold moisture longer – which is probably why I saw moss in those areas. The black color will hold the heat longer, causing your attic to get warmer and your cooling bill to get bigger.

How to clean off the algae and moss.

Knowing the above, I decided to try spraying a bit of chlorine/water mixture onto one inconspicuous shingle to see a) if it would remove the black and b) if it would discolor the shingle. I applied the bleach using an old spray bottle and left it on overnight. The next morning, the shingle was free of black and back to its original color.

Once I knew it might work, I did a little internet searching to see what other issues might arise if I applied a bleach mix to the entire north face of the roof. Aside from the environmental concerns, I didn’t see much that worried me. I did see suggestions to use a cleaner called TSP along with the bleach and water, but couldn’t find that in my normal shopping circles.

My next problem was to figure out how to apply the bleach solution without having to climb the roof (I’m 65 – remember). Luckily, we have an earth berm home and the north face of the roof practically touches the ground. I found a small garden sprayer that used a pressure pump to see if I could reach the top of the roof with a stream of water from it – I could.

To clean the algae and moss from your roof, you will need the following:

A garden sprayer.

I started out with a regular garden sprayer which worked well enough. After I had used it for several days with half water/half bleach, it developed a hole, making it impossible to use. I found a bleach pump sprayer at Home Depot. The plastic is extra thick on it and it was only around $15.

A garden hose.

We had these already as do most of you. I used a sprayer on the end to be able to direct a harder stream of water. I also had cleaned off the limestone landscape rocks on our retaining wall and noticed that a harder stream of water washed off more of the residue.

Don’t use a pressure sprayer on your roof though as you may dislodge the shingles as you are spraying off the bleach.

Bleach and water.

We have a 2300 square foot home with a large steeped roof on the north facing side. I ended up using around 4 gallons of regular bleach. I bought the generic Walmart brand for around $2.50 a gallon. You can also use oxygen bleach – which isn’t as effective but doesn’t have the nasty chlorine and so is a bit easier on the environment. If you use TSP, you can use less bleach. I used 50% water and 50% bleach.

Something to direct the bleach/water runoff away from plantings and creeks.

I had some lengths of PVC pipe left over from a prior project which I put under the downspout to direct the bleach/water onto a gravel drive instead of into the yard. Alternately, you can wet down the area where your gutters drain before you start rinsing and after you finish to keep the damage down.

Time.

Initially I was using a quart sized garden sprayer to lay on the bleach solution. I got a lot of exercise walking from the backyard to the house to refill it! Consequently it took longer. Once I got the gallon bleach sprayer mentioned above, the job went much faster.

You should try to lay the bleach solution down when it is cloudy. Since we had all sunny days when I did this project, I waited until evening to apply it, then left it on over night and rinsed it first thing in the morning. You want the solution to stay wet long enough for the bleach to work to kill the algae and moss.

Using this method, it took me 4 days to do the entire north face of the roof. I did two applications and rinses to kill off the majority of the algae and moss. There are still several faint streaks but I am unwilling to use more bleach on the roof until we get several good rains to give it a more thorough job than my long rinsing could do.

A roof you can reach without walking on it.

Spraying the roof will make it wet (duh). Wet roofs are more slippery. If you have a steep roof, you probably want to think about hiring a roof cleaning company with the right equipment to do the job safely (of course then it will cost you more than my $50).

The process.

The process itself is simple. Assemble your pump container if need be. Mix the bleach solution into the container. Pump up the pressure and set the nozzle to the correct opening (spray for the areas you can reach, stream for the areas further away). Start spraying at the bottom of the roof. If you don’t you will get streaks when the water/bleach runs down the roof. Work your way up. Wait for the bleach solution to work. Wet the grass and landscape where your downspouts drain and then rinse the roof multiple times – I again started at the bottom and wet the roof all the way up prior to rinsing hard at the top of the roof.

Before I treated the shingles, our roof looked old, sad and in need of replacement. Afterward, anyone can see that it looks great and has plenty of life left before we need to replace it.

So if your roof looks like it has stuff growing on it, before you call in a roofer, check out the possibility of cleaning that roof instead.

Have you treated your roof? How did it go for you?