Roof Algae and Moss: Causes, Prevention, and Removal
Those black streaks running down the shingles on the north side of your roof are not dirt. The green fuzzy patches in the shaded areas are not just cosmetic. Algae and moss are alive, they grow, and over time they shorten the life of your roof. The good news is that both are manageable when you understand what they are and how to deal with them.
What Causes Black Streaks on Roofs
The dark streaks you see on so many roofs are caused by an airborne algae called Gloeocapsa magma. The spores travel through the air and land on roofs everywhere. They thrive in humid environments, which describes North Georgia perfectly. The algae feeds on the limestone fillers in asphalt shingles, which is why you see it on shingled roofs and not on metal or tile.
The streaks tend to be worst on the north or shaded sides of a roof because the algae prefers moisture and dies back in direct sun.
What Causes Moss
Moss grows in the same kinds of places as algae but is more visible because it is three dimensional and bright green. It needs even more moisture, which is why it tends to show up under tree cover, in valleys, or anywhere that stays damp.
Unlike algae, moss has roots that work down between shingles. As the moss grows it lifts the shingles, which creates gaps where water can get in.
Why You Should Care
Algae makes a roof look old and dirty. It also slowly degrades the asphalt over time, especially as it spreads.
Moss does more direct damage. The roots lift shingle edges. The moss holds water against the roof, which accelerates wear. Over time moss will cause leaks if it is allowed to grow.
Both also reduce curb appeal and can lower your home value when it is time to sell.
How to Prevent It
The best prevention is built into the roof itself. Modern shingles like GAF Timberline HDZ include StainGuard Plus, which uses copper containing granules to fight algae. The copper slowly leaches over time and prevents algae from establishing.
If your existing roof does not have algae resistance, you can install zinc or copper strips along the ridge. Rain washes a small amount of metal down the roof, which inhibits algae and moss growth.
Trimming back tree cover so more sun reaches the roof and air flows around it helps too. Keeping gutters clean so water moves off the roof properly also reduces the wet conditions that algae and moss love.
How to Remove It Safely
Removal needs to be done carefully. The wrong approach damages shingles or shortens roof life faster than the algae would have.
Do not pressure wash your roof. The high pressure strips off shingle granules and can drive water up under the shingles. It is one of the worst things you can do to a roof.
Soft wash with proper chemicals. A solution designed for roof cleaning, applied at low pressure, kills the algae and moss without damaging the shingles. After application the roof is rinsed with low pressure water. The streaks lighten over the following weeks as rain washes the dead algae away.
Do not scrub or scrape moss. Pulling moss off by hand or with a brush usually pulls granules and shingle pieces with it. Soft wash treatment kills the moss and lets it dry out and fall off naturally.
Hire a professional. Roof cleaning is more dangerous than it looks. Combining slick chemicals with steep wet surfaces leads to falls. A roofing or roof cleaning professional has the right equipment, products, and safety gear.
When Cleaning Is Not the Answer
If your roof is heavily covered in moss and algae, the underlying shingles may already be damaged. In some cases the more cost effective answer is replacement, especially if the roof is approaching the end of its life anyway. A professional inspection helps you weigh the options.
Roofing Georgia Can Help
We can assess what is going on with your roof and recommend the right approach. If a cleaning will solve the problem, we can point you to trusted professionals. If the roof is past the point where cleaning helps, we can talk about replacement options with algae resistant Timberline HDZ shingles that will stay clean longer.
Call Roofing Georgia at 770-874-7663 or visit roofinggeorgia.com for a free inspection.