Moss is the green, fuzzy growth that shows up on shaded, damp roofs, and it is more than an eyesore. Unlike the flat black algae streaks, moss is a real plant that holds water against your shingles and lifts their edges, which leads to rot and leaks over time. It is worth removing, and worth removing gently. Here is how to do it without damaging the roof.
Moss versus algae
It helps to know which one you have. Algae is the flat, dark streak that mostly affects curb appeal, which we cover in black streaks on your roof. Moss is the raised, green, mounded growth, and it is the more damaging of the two, because it holds moisture and can lift the leading edges of shingles.
Where moss grows
Moss favors cool, damp, shaded roofs, especially the north-facing side and areas under overhanging trees. It is less common in the hot, dry parts of Texas and more of an issue in consistently humid, shaded spots.
How to remove it safely
The goal is to kill and lift the moss gently, never to blast or scrape it:
- Pick a cool, cloudy day, and wet the surrounding plants first.
- Spray the moss with a 50/50 mix of laundry-strength bleach and water, or a commercial moss remover. A little dish soap helps it cling.
- Let it sit according to the product directions, usually 15 to 30 minutes.
- Gently sweep or brush the moss downward with a soft brush, following the direction of the shingles. Brushing upward lifts and breaks them.
- Rinse with low-pressure water, and rinse the plants again.
Never pressure wash, and never brush upward
A pressure washer strips the granules and drives water under the shingles, causing immediate leaks. Brushing against the shingle direction tears them loose. Both do more damage than the moss itself.
How to keep moss from coming back
Moss returns wherever it stays damp and shaded, so prevention is about light and dryness:
- Trim trees back to let sunlight reach the roof.
- Keep gutters and valleys clear so water drains and debris does not hold moisture.
- Consider zinc or copper strips near the ridge, best added when you replace the roof, since the metal ions discourage regrowth.
What it costs, and when to call a pro
Doing it yourself costs very little in supplies, mostly the bleach, a sprayer, and a soft brush. A professional moss removal usually runs around 0.20 to 0.75 dollars per square foot, often about 300 to 525 dollars for an average roof, and more for heavy growth. If your roof is steep, the moss is widespread, or you suspect rot underneath, call a pro rather than risk a fall. It is also worth checking for a soft deck or a hidden leak underneath, using our guide to finding a roof leak.
“Moss is a plant that lifts your shingles and holds water. Kill it, brush it downward gently, and never let a pressure washer near your roof.”
Part of a longer-lasting roof
Clearing moss and algae is one piece of keeping a roof healthy for the long haul. For the full set of habits that add years, see how to make your roof last longer.
With Hommy you can post a job once and get roof cleaning, inspections, and repairs from vetted local roofers, each with real ratings from other homeowners, so moss never gets the chance to do real damage.
