If you notice black streaks, green patches, or dark staining on your roof, you may be dealing with mold, algae, mildew, or moss. These types of growth can make your roof look worn and may also signal that moisture is lingering on the surface longer than it should.
The right response depends on the type of growth, the roofing material, and the overall condition of the roof. Just as important, roof cleaning should be approached carefully to avoid damaging shingles or creating a safety hazard.
What is growing on your roof?
Many homeowners refer to any dark or green roof staining as mold, but the issue may actually be algae, mildew, or moss. Each can affect the appearance and condition of the roof in different ways.
Common signs include:
- Black streaks on shingles
- Green patches in shaded areas
- Mossy buildup holding moisture against the roof
- Discoloration or staining that spreads over time
A professional roof inspection can help identify the growth and determine whether the roof has been damaged.
Why roof cleaning should be handled carefully
Cleaning a roof the wrong way can do more harm than good. Aggressive methods may remove protective granules, damage shingles, or shorten the life of the roofing system.
Safety is also a major concern. Walking on a roof, using ladders, and handling cleaning products can create real risks for homeowners.
For those reasons, roof cleaning is often best left to trained professionals. According to the National Roofing Contractors Association, it's not a task that should be taken on as a DIY job and they suggest leaving it to the professionals. But if you are determined to take this project upon yourself, first make sure you know and understand the statistics surrounding ladder falls and injuries - that information alone may give you pause before continuing.
Avoid pressure washing asphalt shingles
Pressure washing can be too harsh for many roofing materials, especially asphalt shingles. High-pressure water can strip away the protective granules that help the roof resist weather and aging. When it comes to cleaning the roof of your home, you can trust the power of a hose attached to a nozzle more than that of a power washer. Power washers are notorious for damaging shingles due to the strong force from which the water sprays out.
When roof cleaning is needed, gentler methods are typically the safer approach.
Use roof-safe cleaning methods
The right cleaning method depends on the roof type and the severity of the growth. In many cases, professional roof cleaning solutions and low-pressure application methods are used to treat algae, mildew, or mold without unnecessarily damaging the roofing material. A bleach and water solution is an effective way to clean an algae-covered roof. Trisodium phosphate mixtures, commonly referred to as TSP, are an effective cleaning solution that can be used when other agents have been unsuccessful.
The goal should not just be to improve appearance, but to do so in a way that protects the life of the roof.
Address the conditions causing the problem
Removing visible growth is only part of the solution. To help prevent it from returning, it is important to address the conditions that allow moisture to remain on the roof.
Helpful steps may include:
- Cleaning gutters and downspouts
- Trimming overhanging branches
- Reducing shade where possible
- Improving attic ventilation
- Scheduling regular roof inspections and maintenance
These steps can help the roof dry more effectively and reduce future buildup.
When to call a roofing professional
It is a good idea to contact a roofing professional if:
- Growth keeps returning after cleaning
- Shingles are curling, cracking, or losing granules
- Moss is thick or widespread
- You are seeing staining inside the attic or home
- You are unsure whether the roof surface can be safely cleaned
A professional can evaluate whether the issue is cosmetic, moisture-related, or a sign that the roof needs repair or replacement.
Protect your roof with the right maintenance
Roof cleaning is one part of protecting the life of your roofing system. Regular roof inspections and repair, gutter maintenance, and timely repairs all play an important role in preventing moisture-related issues from getting worse.
Pickard Roofing helps homeowners in Raleigh, Durham, Chapel Hill, and across the Triangle identify roof issues early and recommend the right next steps. If you are concerned about mold, algae, or moss on your roof, contact our team to schedule a roof evaluation.
At Pickard Roofing, we think Design. Craft. Renew. We are experienced in all types of roofing systems- and provide the right roofing design and selective craftsmanship for renewing our customer’s assets. We invite sustainable building customers to give us a call for your free evaluation. For over 90 years Pickard Roofing Company has installed countless metal, tile, slate, TPO, EPDM, and all types of shingle roofing in the Triangle. Our services include residential, commercial, custom architectural metal fabrication, and historical renovation.
