You’ve probably noticed them — dark streaks running down the slope of your roof, or green fuzzy patches growing near the ridge in shaded areas. Those dark streaks are algae. The green patches are moss. And while they’re related, they behave differently and require different responses.

Black Streaks: Gloeocapsa Magma Algae

The dark streaks that run vertically down many roofs in Fort Wayne are caused by a blue-green algae called Gloeocapsa magma. This algae feeds on the limestone filler in asphalt shingle granules. The algae produces a dark pigmented sheath to protect itself from UV radiation, creating the visible black streaking.

Does Algae Actually Damage Shingles?

In its early stages, algae staining is primarily cosmetic. However, over time, dark algae absorbs more heat from the sun, raising surface temperature and potentially shortening your roof’s lifespan. Algae can also contribute to granule loosening. And algae-stained roofs look old and neglected, hurting curb appeal and resale value.

Moss: The More Dangerous Problem

Moss is a plant with root-like structures that actually grip and penetrate roofing material. It thrives in consistently damp, shaded conditions — north-facing slopes, under overhanging trees, in valleys where debris collects.

How Moss Damages Roofs

Moss holds moisture against the shingle surface like a sponge, accelerating material degradation. It grows under shingle edges and lifts them, breaking the adhesive bond and creating gaps where wind-driven rain can enter. Once moss lifts a shingle edge, it creates a channel for water to reach the underlayment and roof deck — becoming a source of roof leaks.

In winter, water trapped by moss undergoes freeze-thaw cycles that compound the damage, lifting shingles further and cracking the material.

How to Clean Algae and Moss from Your Roof

For Algae (Black Streaks)

A 50/50 mixture of water and oxygen bleach (not chlorine bleach) applied with a garden sprayer is the most effective and shingle-safe cleaning method. Spray, let it sit 15-20 minutes, and rinse with a garden hose at normal pressure. Do not use a pressure washer — it blasts granules off shingles and forces water under edges.

For Moss

Physical removal combined with chemical treatment is necessary. Gently brush moss off using a soft-bristle brush, working from top to bottom. After removing the bulk, apply a moss-killing solution (zinc sulfate or potassium salts of fatty acids).

Preventing Future Growth

Trim overhanging branches. Better sun exposure keeps the roof drier.

Keep the roof clean of debris. Leaves and organic debris trap moisture and provide nutrients.

Ensure proper ventilation. A well-ventilated attic keeps the roof deck temperature closer to outside air, reducing condensation. Check your ventilation system.

Install zinc or copper strips. Metal strips along the ridge release trace amounts of metallic ions when it rains, inhibiting algae and moss growth.

Choose algae-resistant shingles. When it’s time for roof replacement, consider shingles with built-in algae resistance. These products contain copper granules that continuously inhibit algae growth.

When to Call a Professional

If moss has visibly lifted shingles or grown thick enough to create water channels under the shingle edges, it’s time for a professional assessment. Big Dog Roofing provides free roof inspections for Fort Wayne homeowners concerned about algae, moss, or any other roof condition.

Concerned about growth on your roof? Call Big Dog Roofing at 260-999-0347 or schedule your free inspection online.