How to Clean and Prevent Moss on a Roof
Safely remove thick moss growth from asphalt shingles using gentle agitation and eco-friendly wash, then install zinc inhibitor strips along the ridge.
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🧰 Required Tools & Equipment
- ✓ Extension ladder
- ✓ Safety harness with roof anchor
- ✓ Soft-bristle deck brush
- ✓ Garden pump sprayer
- ✓ Garden hose with spray nozzle
- ✓ Hammer
- ✓ Caulk gun
📦 Materials & Supplies
- ✓ Biodegradable roof moss cleaner
- ✓ Zinc moss prevention strips
- ✓ 1-1/4 inch galvanized roofing nails
- ✓ Roofing asphalt sealant
⚠️ Safety Checkpoints & Warnings
- • Wet moss on asphalt shingles is extremely slippery; always stay tied off with a rated harness or work from a secured ladder.
- • Do not use a pressure washer; high pressure strips asphalt granules and voids shingle warranties.
- • Protect ground-level landscaping by pre-soaking plants with fresh water and covering with tarps before spraying cleaning chemicals.
📋 Step-by-Step Guide (5 Steps)
Set Up Ladder and Fall Arrest System
Set your extension ladder on firm, level ground using a 4-to-1 angle ratio and secure the top rungs to the fascia or gutter with ladder straps. Install a temporary roof anchor into a rafter at the roof ridge and clip your harness lanyard into the lifeline before stepping onto the roof surface.
- • Ladder extends 3 feet past the roofline and is strapped tight.
- • Harness tether is taut and connected to an anchored ridge bracket.
- • Stepping onto mossy, wet shingles without harness tethering.
Gently Brush Loose Moss Down the Slope
Using a soft-bristle deck brush on an extension pole, brush the moss downward in the direction of the shingle overlap. Apply light pressure to dislodge clumps without gouging the shingle edges or scraping off the mineral granules.
- • Thick green mats of moss are broken free and resting in gutters or on tarps below.
- • Asphalt shingles remain flat without lifted edges or bald black spots.
- • Brushing upward against shingle flaps, snapping or creasing the shingles.
- • Using a stiff wire brush that strips away the asphalt granules.
Apply Moss Cleaner with Pump Sprayer
Mix the biodegradable roof cleaner with water according to manufacturer ratios in a clean pump sprayer. Spray a thorough, soaking coat across all affected shingles starting from the top and working down, letting the solution dwell for 20 to 30 minutes to penetrate root structures.
- • Even, wet sheen covering all treated roof sections.
- • Moss turning from vibrant green to a pale, yellowish-white color.
- • Applying solution in direct hot sun, causing it to dry before killing the roots.
- • Allowing overspray to settle on dry garden plants below.
Rinse Roof Downward at Low Pressure
Attach a multi-pattern nozzle to your garden hose and set it to a broad spray or gentle fan. Rinse the remaining chemical and dead moss residue down the roof slope, keeping the stream pointed downward at all times to prevent water from pushing underneath the shingle tabs.
- • Clean, clear rinse water flowing into the gutter system.
- • Shingle surfaces clean of brown residue and loose organic slime.
- • Spraying water sideways or upward beneath the shingle laps.
- • Using a pressure washer tip that blows through the roof felt.
Install Zinc Prevention Strips Under Ridge Caps
Tuck a 2-to-3-inch wide zinc strip underneath the bottom edge of the ridge cap shingles, leaving 1 to 2 inches exposed to rainfall. Secure the strip every 12 inches with galvanized roofing nails, then dab roofing sealant over every nail head and under the shingle edge to seal nail penetrations and bond the tabs.
- • A straight, silver zinc strip runs continuously along the ridge line.
- • All nail heads are fully encapsulated beneath smooth black dabs of roofing sealant.
- • Leaving nail heads exposed to the weather without asphalt sealant dabs.
- • Tucking the entire strip completely underneath shingles so no metal is exposed to rain.
Credit: inspired by an original tutorial by This Old House — watch the original on YouTube.
Don’t have everything?
- No Zinc moss prevention strips? Solid bare copper wire or copper flashing strips
- No Biodegradable roof cleaner? Equal parts powdered oxygen bleach mixed with warm water