If you notice unusual discoloration or colorful patches on your roof, you could be dealing with mildew or mold, two common types of fungi that can significantly impact your roof's appearance. These dark spots are often caused by similar conditions, such as moisture and poor ventilation, but there are slight differences between the two. Mold tends to be more problematic and is harder to remove.
Addressing these pesky problems when they first appear is key, and learning to distinguish mold vs. mildew can help you treat them more effectively.
Understanding Mildew: The Surface Dweller
Mildew typically appears as a thin, powdery or fluffy substance on the roof in shades of white, gray, or yellow. While it's commonly mistaken for algae or mold, its lighter color can help differentiate it. Unlike mold, which can penetrate more deeply into roofing materials, mildew usually remains on the surface, making it much easier to get rid of.
Mildew thrives in warm, damp areas with poor ventilation and is most commonly found in shaded spots, such as under overhanging tree branches or in roof valleys where standing water and poor airflow are common.
Although mildew is primarily a cosmetic issue, causing unsightly discoloration and stains on your roof, it's not something you should ignore. If left untreated, the spores can spread, potentially leading to more widespread growth.
Understanding Mold: The Infiltrator
One of the most noticeable differences you can spot when comparing mold vs. mildew is their color. Mold tends to have a slimy or fuzzy texture and often appears in darker shades, like black, green, brown, or dark gray. These deeper hues can make it easier to differentiate mold from the lighter shades that mildew produces.
While both thrive in damp, humid environments, mold is less likely to appear on roofs—but when it does grow, it's much more damaging. Mold can penetrate porous roofing materials and spread beneath shingles, eventually reaching the roof decking and even the attic. This can lead to rot, structural damage, and costly repairs. Unlike mildew, which remains on the surface, mold embeds itself deeper, making it more challenging to remove.
In addition to damaging your roof and affecting its appearance with dark, unpleasant-looking patches, mold can pose health risks. Mold spores release allergens and mycotoxins, which can cause respiratory problems in some people, especially those who are immunocompromised.
Mold vs. Mildew at a Glance
Refer to this mold vs. mildew chart to quickly assess which type of fungi you might be dealing with and its potential risks.
Mold | Mildew | |
Color | Black, green, brown, gray | White, gray, yellow |
Appearance | Slimy, fuzzy | Powdery, fluffy |
Roof Damage Level | Severe, as mold can infiltrate materials below the surface | Low, as mildew typically remains on material surfaces |
Growth Patterns | Spreads quickly | Spreads slowly |
Health Impacts | Can cause more severe allergic reactions and respiratory issues (e.g., asthma), skin and eye irritation, and infections, particularly in immunocompromised individuals | Can cause milder allergic reactions and respiratory problems (e.g., coughing, headache, and sore throat), and skin and eye irritation |
What to Do If You Find Growth
When you spot mold, mildew, or even moss on your roof, it's best to seek removal as soon as possible. Moss doesn't die off in the winter, and it's no different for mold and mildew—they just become dormant. When dealing with mold vs. mildew, the next step is the same: to remove them permanently instead of waiting for them to disappear.
Removing mold and mildew is a job best left to a professional. While it may be tempting to tackle it yourself, eliminating the existing mold or mildew without addressing the root cause can lead to recurring issues. This is especially true for mold, which is more invasive and difficult to eliminate. A qualified roofing professional can conduct a thorough inspection, perform necessary testing to diagnose what type of fungi you're dealing with, and implement a long-term solution, not just a surface-level fix.
The steps to remove mold vs. mildew are similar, but they differ in key ways. Both processes require protective gear, including safety gloves, goggles, and a mask. The area around the roof must be prepared ahead of time by laying down tarps to protect nearby plants and landscaping from exposure to cleaning solutions. The professional will then use a ladder to access the roof safely and spray the affected areas with the solution, allowing it to sit for about 30 minutes.
Mold requires deeper saturation since it can penetrate below the surface. After letting the solution sit, the contractor will carefully scrub the areas with a soft-bristle brush. Mildew generally lifts with light scrubbing, but mold may require more effort since it's more securely attached.
Once the scrubbing is complete, they'll rinse the roof thoroughly to remove the solution and any loosened residue. The final and critical step is a detailed inspection in which your contractor will make repairs as needed. Any roofing leaks or drainage issues that might have led to the mold and mildew growth are addressed at this point to help prevent further infestation.
Prevention Is Key: Maintaining a Healthy Roof
Maintaining a healthy roof and addressing the underlying factors that lead to mold and mildew can help save you the time and trouble it takes to deal with them. One of the most effective prevention strategies is ensuring proper ventilation. Good airflow helps prevent the humidity and moisture buildup that mold and mildew thrive on. A well-ventilated roof maintains a stable temperature and resists trapping excessive heat. Ensuring you have sufficient roof vents, such as soffit vents and ridge vents, allows hot, moist air to escape from the attic while drawing fresh air into your home.
Regular roof cleaning is another smart preventive measure. Hiring a contractor to clear debris, such as leaves and branches, can help prevent clogged gutters and roof valleys that can trap moisture and lead to fungal growth. At the first sign of a roof leak, such as broken shingles, damaged flashing, or damp spots in the attic, contact a roofing professional for repairs. Water damage can be quickly followed by mold if left unaddressed.
The preventive measures you take now can minimize the need for mold or mildew remediation later on. Ensuring proper roof ventilation, scheduling routine roof cleaning, and addressing necessary repairs promptly can help reduce the risk of mold and mildew on your roof and help extend its lifespan. These efforts help your roof perform effectively, potentially saving you from costly repairs or premature replacements in the future.
Mold vs. Mildew: Dealing with Whichever Comes Your Way
While mold and mildew may appear similar at first glance, they can affect your roof quite differently. Mold typically appears in black, green, brown, or gray patches and is far more destructive, as it can penetrate beneath the surface of your roofing materials, spread quickly, and even pose health risks due to airborne spores. Mildew, which usually grows in white, gray, or yellow patches, tends to stay on the surface, making it more of a cosmetic issue and less of a structural concern (and less of a headache to remove).
Whether you're dealing with mold vs. mildew, hiring a professional roofer is the safest and most effective option for removal. A qualified contractor can help eliminate the growth and address any underlying causes to help prevent future infestations. If you need help finding an experienced roofer, look for a GAF-certified contractor near you.
