Given the right conditions, moss can grow almost anywhere on a home's exterior, including roofs, siding, masonry and window glass. Humidity, moisture and limited sunlight provide moss with the necessary conditions to flourish. Left to grow, moss spreads to window frames and siding, where it causes damage to the substrate. Moss restricts the airflow and light over the substrate, which leads to rot and corrosion. Removing moss from window glass is essential to protecting the rest of the home from damage.
Lay a tarp or plastic sheeting over nearby plants and flowers to protect them from the moss removal products. If a tarp or plastic sheeting will break the plants, thoroughly soak the plants and surrounding soil with plain water to limit the plants' absorption of moss-killing products.
Mix equal amounts of chlorine bleach and water in a spray bottle, or use a commercially available moss and algae killer. Some moss and algae killers come as a ready-to-use product, while others require dilution. Follow the manufacturer's directions to dilute the moss and algae killer safely and correctly.
Spray the moss killer of your choice directly on the moss. Wait 10 to 15 minutes.
Scrape away moss with a plastic spatula, plastic putty knife or soft-bristled scrub brush. Rinse the utensil in a bucket of warm soapy water often to prevent the redistribution of moss on other surfaces. Use an old toothbrush to scrub moss that has infiltrated small crevices where the window glass meets the window frame.
Rinse the window glass with plain water to remove moss-killer residue. Clean the window with glass cleaner to remove streaks and water spots.
Wear eye protection and rubber gloves when removing moss. Trim overhanging trees, shrubs and vines that block the light and airflow to prevent the return of moss.
Avoid using chlorine bleach on windows with aluminium frames; the bleach will damage aluminium. Do not use a power washer or high-pressure nozzle, as the force of the water can break, crack or unseat windows from their frames. Avoid using metal scrapers on window glass; metal may leave scratches on the glass surface.