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Moss holds moisture against your roof, which can cause rot, mold, and other structural damage to your home. In this article, we’ll explore the best methods to remove moss from your home’s exterior and keep it from returning. In the video above, This Old House general contractor Tom Silva cleans a mossy roof and installs preventative measures to help a homeowner avoid costly future roof repairs.
How Moss Impacts Your Roof
Because moss thrives in damp and shaded areas, certain roofs are ideal breeding grounds for it. North-facing roof slopes and homes in cool, damp climates are particularly at risk.
If left alone, moss can be quite destructive. When moss holds moisture against your roof’s surface, it prevents the shingles from drying properly. This trapped moisture can lead to algae, mold, and mildew growth, which can further damage the shingles and underlying materials. Moss growth can potentially lift shingles, making your roof more susceptible to wind damage and leaks and creating an environment perfect for major water damage inside your home.
Safety Precautions for Roof Work
Working on a roof can be dangerous, so make sure you have the right equipment and knowledge before you start roof work. Silva adds a roof anchor to the rafters, wears a harness, and uses a safety line. You can find these at home centers or hardware stores.
Essential Safety Equipment
When working on a roof, always use:
- Safety harness system
- Non-slip shoes
- Sturdy ladder
- Safety glasses
Tips for Safe Roof Work
If you’ve never worked on a roof before, follow best practices for your safety. Always work in dry conditions to reduce the risk of slipping. Keep your workspace organized and free of clutter to avoid tripping hazards. Never work on a roof alone—have someone help you for an extra layer of safety.
Avoid Using a Power Washer
While using a power washer might seem like a quick fix, it can cause more harm than good. Power washers can damage your shingles if the stream is too strong. It will strip away their protective granules and can lead to leaks. Also, it’s dangerous to work on a wet roof, as there are slipping hazards. Instead, stick to gentle manual methods on your roof’s materials.
When To Call a Professional
If you’re uncomfortable with or afraid of heights or lack experience working on roofs, you should consider consulting with a professional. They have the expertise and equipment to safely clean and treat your roof.
Cleaning Moss from Your Roof
Follow these steps to effectively and carefully remove the moss from your roof. Pay special attention as you work to avoid damaging the shingles.
Preparing the Area
Before starting the cleaning process, cover plants and grass below the roof with tarps or spray them down with water. This will protect them from any cleaning solutions. Then set up your ladder securely so you can safely reach the roof.
Attaching the Harness
Put on your safety harness and attach it to a roof anchor. Follow the manufacturer’s instructions to make sure your harness is on correctly and is securely attached to the roof. You can choose from a standard rope and latch harness or a retractable pulley system harness. The pulley harness senses a sudden jerk (in this case, a fall) and tightens up similar to a seatbelt to prevent you from falling further.
Follow the manufacturers’ directions on how to install the harness. For security, make sure the brackets are attached to your roof’s rafters.
Removing Loose Moss
Start by gently removing loose moss. Silva does the following:
- Use a soft-bristled push broom to sweep away as much loose moss as possible.
- Work from the top of the roof down to avoid stepping on wet areas.
- Be careful not to damage or lift shingles while sweeping.
Installing the Zinc Strip
Silva installs a zinc strip, available at most hardware stores, near the roof’s ridge. When it rains, water will pick up the particulates in the zinc and deposit them along the roof, preventing more moss from growing. Copper strips are a good alternative if zinc isn’t available.
Follow these steps to install the strip:
- Roll out zinc strips near the roof ridge. Lay half under the shingles and let the other half be exposed over the roof. Be careful working around the edges as they’re sharp.
- Nail roofing nails about halfway through the zinc strip, just to get it held in place.
- Apply a bead of roofing cement around each nail before nailing them all the way through. This seals the nail hold completely.
- Once the nail is all the way through, add another bead of roofing cement on top of the nail. Repeat this process for all the nails.
Applying Cleaning Solution
After removing loose moss and installing the zinc strip, apply a cleaning solution. In the video, Silva sprays down the roof using a solution of water and bleach. He starts at the bottom of the roof and works to avoid slipping:
- Mix 1/3 gallon of bleach with 1 1/2 gallons of water in a pump sprayer.
- Spray the solution on the mossy areas, starting at the bottom.
- Allow the solution to sit for a few days to kill the remaining moss.
Alternative Cleaning Solutions
If you prefer an eco-friendly approach, there are alternatives to traditional bleach solutions. Oxygen bleach, vinegar mixed with water, and commercial eco-friendly roof cleaners work well to kill moss without harming the environment. When choosing a product, look for labels that indicate safety for plants and animals.
Rinsing and Final Steps
After allowing the cleaning solution to sit, it’s important to rinse the roof thoroughly. Use a garden hose with a gentle spray to wash away dead moss and cleaning residue. Make sure to wash all the solution away to avoid harming plants around your home.
Preventing Future Moss Growth
After cleaning your roof, you should take a few extra steps to prevent moss from returning.
Trimming Overhanging Branches
Reduce the shade cover over your roof by:
- Trimming branches that hang over the roof to prevent moss growth as well as physical damage caused by falling limbs
- Removing debris that builds up on the roof, such as branches and leaves
- Allowing more sunlight to reach the shingles
Regular Roof Maintenance
Maintain your roof to discourage moss growth:
- Clean gutters regularly
- Remove debris from the roof surface
- Inspect for signs of moss growth annually
- Install a zinc strip to make it difficult for moss to grow
Seasonal Roof Maintenance
In the spring, inspect for any damage or moss growth that developed over the winter. In the fall, clear your roof of leaves and other debris to prepare for the wet season.
