Roof Soft Washing

The stains are alive, and they are costing you shingles

Gloeocapsa magma is an algae that arrived in the Northeast decades ago and never left. It feeds on the limestone filler used in modern asphalt shingles, spreads down the roof with every rainfall, and shows up as those dark vertical streaks that make a fifteen-year-old roof look forty.

The cosmetic damage is the part you notice. The expensive part is that the colony holds moisture against the shingle and raises surface temperature, and both of those shorten the life of a roof you paid five figures for. Left alone, it also gives moss and lichen somewhere to root, and lichen puts down structures that pull granules off when it finally lets go.

Why nobody should pressure wash a roof

Asphalt shingles are protected by a layer of ceramic granules. Those granules are what shed UV and rain. A pressure washer takes them off, and once they are in the gutter, the shingle underneath is exposed and aging fast. The Asphalt Roofing Manufacturers Association is unambiguous about it, and most warranties are void the moment high pressure touches the roof.

Soft washing applies a cleaning solution at less than garden-hose pressure, kills the organism, and lets rain carry it away. Nothing abrades. Nothing is dislodged. It is slower and it costs more in solution, and it is the only method we will use.

What the day looks like

• Gutters are checked and cleared first, so runoff has somewhere to go.
• Beds, lawn and any water features below the roofline are soaked and covered as needed.
• Solution is applied evenly from the ridge down, section by section, and left to dwell.
• Everything below the roof — siding, windows, walkways, driveway — is rinsed clean of runoff.
• We flush the gutters and downspouts a second time on the way out.

Moss, lichen and the two-week rule

Algae staining disappears fast. Moss and lichen have physically attached themselves to the shingle and need to die, dry, and release, which takes two to four weeks of normal weather. Pulling or scraping them off early takes granules with them. We would rather you wait and keep the roof.

Gutter faces are a separate job

The dark vertical striping on the front of aluminum gutters is not the same problem and does not come off with a roof wash. It is an oxidized film that needs a dedicated brightening treatment — see gutter cleaning and brightening if yours have gone tiger-striped.