Moss & Algae Removal

Moss and Algae Are Slowly Destroying Your Roof

Moss and algae are not just cosmetic problems — they are actively degrading your roofing material. Algae feeds on the limestone filler in asphalt shingles, causing granule loss and premature aging. Moss lifts shingle edges and forces water underneath, creating leak paths. Lichen bonds to the roof surface and causes erosion as it grows. Left untreated, these organisms shorten your roof’s lifespan by years.

We remove moss, algae, and lichen using a biodegradable treatment that kills the organisms at the root without damaging shingles, tiles, metal, or cedar. The treatment also prevents regrowth for 12 to 24 months, keeping your roof clean and protected between maintenance visits.

What Is Growing on Your Roof

Organism	Appearance	What it does
Algae (Gloeocapsa)	Black streaks running down the roof	Feeds on limestone filler, causes granule loss
Moss	Green, raised, cushion-like clumps	Lifts shingles, traps moisture, causes rot
Lichen	White or green crusty patches	Bonds to surface, causes erosion
Mildew	Thin, powdery film	Cosmetic, indicates moisture

These organisms thrive in shaded, moist environments. North-facing slopes and roofs under tree canopy are the most affected. Spores spread through wind and rain, so one affected roof can seed growth on neighboring homes.

How We Remove Moss and Algae

Our treatment kills the organisms and prevents regrowth without the damage caused by scraping or pressure washing.

1. Assessment — we identify the type and extent of growth; heavily moss-covered areas need more aggressive treatment
2. Application — a biodegradable moss and algae treatment is applied to the affected areas using low-pressure sprayers
3. Dwell time — the solution sits for 15 to 30 minutes, killing the organisms at the root; moss turns brown as it dies
4. Gentle removal — dead moss is gently brushed or rinsed away with low-pressure water; we do not scrape or pry moss off, which damages the shingle surface
5. Preventive treatment — a residual algaecide is applied to the cleaned surface to inhibit regrowth for 12 to 24 months
6. Gutter flush — gutters and downspouts are flushed to clear debris and treatment residue
7. Landscaping rinse — surrounding plants and landscaping are rinsed to remove any treatment overspray

Moss and Algae Treatment Costs

Service	Typical range
Light algae treatment	$200 – $400
Moderate moss and algae treatment	$400 – $700
Heavy moss removal	$600 – $1,200
Preventive treatment (annual)	$200 – $400
Combined with full roof cleaning	$400 – $900
Zinc strip installation	$300 – $700

Costs depend on the severity of growth, roof size, and accessibility. Heavy moss buildup on a steep roof requires more time and treatment solution.

How to Prevent Moss and Algae From Coming Back

• Keep trees trimmed — reduce shade and debris that promote growth; cut back branches that overhang the roof
• Maintain gutters — clogged gutters create moisture that feeds organic growth along the eaves
• Install zinc or copper strips — metal strips along the ridge release ions that inhibit moss and algae; effective for 15 to 20 feet downslope
• Apply preventive treatment — a residual algaecide applied after cleaning keeps growth suppressed for 12 to 24 months
• Schedule regular maintenance — annual or bi-annual inspections catch regrowth early
• Improve drainage — ensure roof valleys and gutters flow freely to prevent standing water
• Address shade — where possible, trim or remove trees that cast persistent shade on the roof

Why Moss and Algae Grow on Roofs

Moss and algae need three things to grow: moisture, shade, and a food source. Roofs that stay damp after rain, face north, or sit under tree canopy provide all three. Asphalt shingles contain limestone filler, which algae feeds on. Moss anchors to the shingle surface and holds moisture against it, creating a self-sustaining cycle of growth and moisture retention.

The longer the organisms grow, the more damage they cause. Early treatment is always cheaper and more effective than waiting until the growth is severe.

Climate Factors

• Pacific Northwest — persistent rain and shade make moss a year-round problem
• Southeast — warm, humid summers promote algae growth on shaded roof slopes
• Northeast — freeze-thaw cycles break apart moss-damaged shingles
• Mountain regions — extended shade from surrounding terrain and heavy snow create ideal conditions

How Moss and Algae Damage Different Roof Types

Roof type	Moss damage	Algae damage
Asphalt shingles	Lifts edges, forces water under, causes rot	Feeds on limestone filler, causes granule loss
Cedar shakes	Holds moisture against wood, accelerates rot and splitting	Stains the surface, darkens the wood
Metal roofing	Traps moisture at fastener points, causes corrosion	Cosmetic staining, rarely causes structural damage
Tile (concrete or clay)	Forces water under tiles, lifts them from the underlayment	Cosmetic — darkens the tile surface
Slate	Lifts individual slates from their hooks, causes slippage	Minimal — slate is too dense for algae to penetrate

Moss is the more destructive organism because it physically lifts roofing materials. Algae is primarily cosmetic on most roof types but accelerates shingle aging by consuming the limestone filler. Both organisms hold moisture against the roof surface, which accelerates weathering and creates conditions for rot and mold.

DIY vs. Professional Moss Removal

DIY may work when:

• Growth is light and limited to a small area
• You can safely access the roof with proper fall protection
• You use a manufacturer-recommended moss treatment, not bleach or detergent

Call a professional when:

• Moss is thick and widespread across multiple roof slopes
• Lichen is present — it bonds to the surface and requires specialized treatment
• The roof is steep or more than one story
• The roof is older and additional granule loss from scraping would accelerate deterioration

Professional treatment costs more upfront but delivers better results, prevents regrowth, and protects the roof surface from damage caused by aggressive scraping or improper chemicals. The investment in professional treatment is modest compared to the cost of premature shingle replacement caused by aggressive DIY removal. Professional treatment also includes a preventive application that suppresses regrowth for 12 to 24 months, keeping your roof cleaner longer between maintenance visits. We use biodegradable treatments that are safe for your landscaping and the environment.

Moss or algae on your roof? Call us or request a free assessment — we will identify the growth, treat it safely, and apply a preventive treatment to keep it from coming back.