DEAR TIM: Roof cleaning
needs to be done at my home. I have a newer asphalt shingle roof, but
parts of it are getting covered with moss, lichens and algae. It is
really distressing, as it makes my house look like it is being
neglected. Is a pressure washer a great tool for cleaning roof
shingles? Will it remove all of this growth? A neighbor told me a
pressure washer will ruin my shingles. Are there other cleaning
alternatives? Once the roof is clean, how do I prevent the stuff from
coming back? Tom B., Whittier, NC
DEAR TOM: Welcome to the
world of organic chemistry. I'll bet the north, northwest and possibly
west-facing sections of your roof are the ones that look bad, while the
remaining parts of the roof look like new. What's more, my guess is the
parts of your roof that are the worst get shade from some large trees.
I know this, because I have the exact same problem as you do. Parts of
my roof look like the Amazon rain forest.
Wind
broadcasts spores, they can drop from trees and birds can deliver them
to a roof surface. The abundant water you get from periodic rainfall
fuels the growth of the moss, lichens and algae. Since the north,
northwest and west sections of your roof stay in the shade during the
early part of each day, the dew that develops on the roof at night does
not evaporate quickly. This morning moisture quenches the
thirst of the mini-vegetable garden up on your roof. The other sections
of your roof dry too quickly and the moss, lichens and algae die of
thirst.
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| You can use a pressure washer to clean moss, lichens and algae from asphalt shingle roofs. But, you must be careful! PHOTO CREDIT: Brent Walker |
I have also heard urban
legends about pressure washers causing permanent damage to asphalt roof
shingles. I know for a fact that pressure washers can damage concrete,
so it would seem likely they might harm shingles. But since I know how
to quickly and easily replace one or more roof shingles, I decided to
do a test of my own. What's more, I felt my roof would be a good one to
test since it is now twenty-years old, and at the end of its useful
life. I also decided to test some new shingles to see if the pressure
washer blasted away many or all of the colored
granules.
The roof-shingle-cleaning test started
with a gasoline-powered pressure washer that develops 2,500 pounds per
square inch of pressure while delivering 2.4 gallons of water per
minute. I equipped the pressure washer spray wand with a 25-degree tip.
This tip is used for general-purpose cleaning.
The
results of the test were astonishing. I was able to remove all of the
moss, lichens, algae and twenty years of dirt with the pressure washer.
No damage was done to the asphalt shingles
whatsoever.
I started with the spray wand tip
about twelve inches from the surface of the shingles and aimed the wand
down the roof. I didn't get any noticeable cleaning results at this
distance. But once I slowly lowered the wand to within 6 inches of the
shingles, the organic growth started to disappear. My suggestion to you
is to carefully clean just one shingle and stop working. Inspect the
shingle for damage.
Walk to another part of your
roof where the shingles look great to see if the clean shingle looks
just like the freshly-cleaned shingle. Rest assured you will readily
spot damage. If you see small or large patches of solid black or
fiberglass mesh, you are ruining your roof.
You can
use a regular garden hose and a scrub brush to clean your roof. It will
be an enormous amount of work to say the least. Always point the garden
hose or pressure washer wand down the roof. Never point it up the roof,
as water can be driven up under the shingles creating massive leaks
inside your home.
You can keep the roof looking like
new once cleaned, by installing strips of copper at the top of the
roof. You need about two to three inches of copper exposed along the
ridge line. If your roofer had installed shingles that contained
invisible copper-coated granules, you would not have to do any of this
work. The slow release of copper on the roof surface prevents the
growth of moss, lichens and algae.
Be extremely
careful working on a roof with water. The water makes the moss, lichens
and algae as slippery as if you had spread oil on the roof. Try to
always work on a dry section of the roof. Work in ribbons that are
maybe two-feet wide going from the ridge line down to the gutter line.
The hoses also are dangerous slip hazards. Use fall-protection
harnesses to ensure you will not get hurt if you
slip.
When you get to within ten feet of the edge of
the roof, stop working and let the freshly-cleaned roof dry. Once the
roof is dry, then reverse the direction of cleaning so you are walking
forward towards the end of the roof, not backwards and falling
off!
