Is Soft Washing Safe for Roof Shingles?

By Gunderson Soft Wash Services · Updated October 15, 2026

Yes. When it is done correctly, soft washing is the gentle way to clean a shingle roof. High-pressure washing is the method that causes damage.

What those dark streaks on your roof are

On many Wisconsin roofs, the black or dark-gray streaks running down from the ridge are algae. Roofs also pick up moss and lichen, especially on shaded slopes under trees and on the north side where the sun rarely dries the shingles. This growth holds moisture against the roof surface. Left alone, it keeps spreading.

Why high pressure is the problem

Asphalt shingles are covered in small mineral granules. Those granules shield the shingle from sun and weather. A strong stream of water can knock granules loose and push water under shingle edges. Roofing manufacturers and industry groups warn against pressure washing shingles for this reason. A roof that loses its granules can age much faster.

How soft washing works instead

Soft washing uses low water pressure, close to what comes out of a garden hose. A cleaning solution does the work. The solution is applied to the roof, left to act on the algae, moss and lichen, and then rinsed off gently. The growth is killed at the source instead of being blasted off the surface.

• Low pressure protects shingle granules, flashing, vents and seals.
• The cleaning solution treats the growth itself, so the roof does not simply regrow right away.
• Landscaping is protected by wetting down plants before and rinsing them after.

What to expect after a roof wash

Some of the stain lifts during the wash. Other streaks fade over the following days and weeks as the treated growth dies and rain rinses it away. The finished result is a roof that looks much closer to how it did when it was new.

What happens if I leave algae on the roof?

Algae and moss keep moisture on the roof and make it look older than it is. Many homeowners also clean the roof before listing a home, because dark streaks stand out in photos and from the street. One Gunderson customer had a roof and gutters cleaned ahead of a sale after a realtor pointed to curb appeal.

Common questions

Can you soft wash a metal roof?

Yes. Soft washing is a gentle way to remove dirt, algae and mildew from many roof types. Tell us the roof material when you request a quote.

Will soft washing damage my shingles?

Soft washing uses low pressure and a cleaning solution, so it avoids the granule loss that high-pressure washing can cause.

Learn more about our roof cleaning service, or see the towns we serve within about 60 miles of Mauston.