Information for Local Property Owners and Service Providers
in Seattle's Ballard Neighborhood

Moss Removal & Treatment Nuances

Allowing moss to grow unchecked on a composite roof drastically shortens its lifespan, sometimes by up to 10 years or more. As the moss expands, its root system wedges underneath the edge of the shingles, breaking the asphalt sealant strip and lifting shingles upward. Once the shingles have dislodged from the sealant, they become highly susceptible to wind-uplift during severe storms — worse, during freezing weather, the water trapped inside the moss freezes and expands, cracking the shingles from the inside out. In Washington state, insurance companies routinely audit properties via aerial drone photography and will threaten to cancel homeowner policies if they detect heavy roof moss overgrowth, as it is a leading indicator of imminent roof failure and hidden dry rot. We alter our methodology based on the structural needs of the property:

• Manual Large Moss Overgrowth Removal

  • Recommended Approach:

    • ​Non-destructive, manual agitation with steel brushes, angled at 30 degrees. (Note: We aim to remove 85% - 90% of the visible moss only. This is to ensure we never remove an unnecessary amount of composite, in order to extend the longevity of your investment).

    • Work from the roof ridge downward, gently scraping away thick moss clusters without gouging the shingles or dislodging the protective mineral granules.

    • Blow and sweep dead moss off the roof with a downward motion.

• Eco-Friendly Sodium Percarbonate Application

  • Recommended Approach:

    • ​Application of granules and/or powder during calm winds, liquid solution during high winds.

    • Spread concentrated, environmentally friendly Sodium Percarbonate across the roof surface in horizontal rows — starting with the peak, and adding horizontal lines in vertical increments of 5-6 feet until you reach the roofline. The chemical absorbs into the composite, killing off the majority of the roots lodged within the cracks between shingles. (Note: Contrary to common concern, rainfall doesn’t inhibit this process — but in fact helps the granules stick to the composite and expand rapidly, reaching maximum effectiveness).

• Comprehensive Gutter Cleaning (Included)

  • Recommended Approach:

    • ​Protection of gutters and rainwater catch systems, as well as preemptive avoidance of clogged downspouts. (Note: We include a thorough clean-up of the grounds immediately surrounding your gutters and roofline in our service, to ensure that no mess remains after we leave the premises).

    • To ensure that dislodged moss and composite don’t immediately clog gutters and downspouts, a full gutter cleaning is always recommended and included in our moss removal service (unless the property has gutter protectors covering all entry to the gutters, in which a thorough sweep and/or blow-off of guards is performed.

• Maintenance Recommendations

  • A full, manual moss removal should be executed every 3 to 6 years, depending on your local tree canopy density and annual inspections to track regrowth.

  • We highly recommend a preventative Sodium Percarbonate treatment once per year at minimum (often performed during annual gutter cleaning.

  • By combining these services at the right times of year, homeowners can avoid the headaches of costly repairs and extend the timeframe until more expensive roof work. In extreme cases, a moss-damaged roof will need to be replaced, which can cost anywhere between $16,000 on the low end to as much as $90,000 or more for 30-40 year stacked shingle roofs or properties with larger footprints.

  • The best time for manual removal is late summer or early fall (August through November). This allows us to clear away the majority of the moss at its most vulnerable, dry state — and apply the protective chemical layer right before the heavy, constant rainfall of the Pacific Northwest winter begins.