Removing harmful moss will help prevent roof damage


Moss is an opportunistic grower that spreads exuberantly across Washington homes during the rainy season.

It damages shingles, retains water and deteriorates the roof. Moss can halve the lifespan of roofs if not treated, according to Luke Rogers, owner of soft-washing company Clean Choice Professional Services, located in Battle Ground.

“Typically, moss starts to grow three to five years after a new roof has gone up,” Rogers said. “Because of how humid and wet it is around here, it’s the perfect environment for moss to grow.”

In the roof-cleaning industry, companies offer brushing, pressure washing and soft-washing services to remove moss.

When moss grows into the shingles, it can lift them, allowing water to seep through and damage the roof. The water sits underneath the shingles and causes rot over time. The mossy shingles are also at risk of wind damage, their lifted corners easily catching wind, Rogers said.

Many roof-cleaning options are available, but some are better than others and cause less damage to the protective sand-layer embedded in the shingles. Removing the sand reduces the lifespan of the roof. The protective layer acts as a “helmet,” reinforcing the roof so it can withstand wind, branches and hail, Rogers said.

Using a stiff metal brush, roof cleaners scrape moss from roofs. Though effective, Rogers cautions property owners about the damage excessive brushing can cause. Brushing digs into the shingles, damaging the sand embedded into the material’s sticky tar surface.

Pressure washing is another common method of roof cleaning. The high-pressure wash blasts moss and grime, deep cleaning the roof. But, it can damage the roof, Rogers said.

“I don’t like any sort of high pressure up on a roof at all,” Rogers said. “Pressure washing will remove a lot of the sand.”

Rogers prefers to soft wash roofs, a method where a gentle stream of water from a garden hose mixed with detergents and chlorine is sprayed onto roofs to remove moss. When sprayed, the moss whitens, dries and flakes off.

“It kills the moss down to the roots,” Rogers said. “We say to give it about three months or so for the moss to flake off and disappear with the wind and the rain.”

Greenery near the house must be protected during the soft-washing process because the detergents and chlorine can damage plants.

A soft-wash cleaning typically costs more than other options and keeps the roof clean for years. With some preventative care, Rogers said property owners can skip cleaning for a few years.

Many preventative measures to keep moss from growing are available, but blowing the roof clean of debris is the best method, Rogers said. Moss needs nutrients and moisture to grow, and dead plant matter and dirt are a good growing medium.

“The moss will grow a lot faster because the leaves are holding moisture on the roof,” Rogers said.

Chemical options, like zinc strips and powdered moss removal, are also available. Rogers recommends against using zinc strips, which require nails and put unnecessary holes in the roof.

“It’s not that effective, and now there’s holes on the roof,” Rogers said.