Managing Moss On Cedar Roofs

Cedar shingles aren't just beautiful to look it; they also provide a stable and durable roofing material that resists the elements. Natural wood shingles made from cedar are naturally resistant to insect damage and rot, but moss buildup can cause water to set on the roof and lead to problems. Fortunately, this issue is easy to avoid with proper roof maintenance.

Prevention Begins at Installation

Prevention is the best step you can take so that moss never becomes a major issue on your roof. Copper or zinc strips can be installed beneath the roof cap when the roof is put on, or your roofer can add these strips to your existing roof. Each time it rains, some of the copper or zinc leaches from the strips and runs down your roof. These materials prevent moss from growing.

Another option during installation is to choose cedar shingles that have been impregnated with preservatives that prevent moss growth.

Managing Trouble Overhead

Moss is more likely in wet climates and in shady locations. Trimming back nearby trees so the sun can shine on your roof can minimize a lot of issues down the road. If you prefer to keep the trees in place, at least take the time to clean the old leaf litter from the roof each fall. Mounds of leaves or tree needles trap moisture, which increases the chances of moss growth and future rot problems. Debris on the roof and in the gutters can also lead to the formation of ice dams during cold weather.

Basic Cleaning

Sometimes moss takes hold, even with your best efforts. You have two options when it comes to cleaning it off:

  1. Pressure washing

  2. Cleaning solution methods

Pressure washing can damage cedar roofs, especially if the pressure is too high or the nozzle isn't held at the right distance and angle. Generally, it's best to have pressure washing done professionally if you aren't experienced in the task.

A general cleaning solution is easier for the DIYer. You can use a zinc-based moss killer for roofs, or mix up a solution of one part bleach to four parts water. Spray the solution on the roof so it kills the moss, and then rinse it and the dead moss off with a garden hose. Keep in mind, bleach solution run-off can kill or damage plants below.

One option some cedar roof owners consider is sealing the shingles to prevent rot and moss. The issue is that waterproof sealers won't allow the shingles to breath, which causes them to dry out and crack prematurely. You can use water repellent sealers, but skip anything that is advertised as waterproof or water-tight. Talk to roofers for more information.