Six weeks after moss treatment in Forest Park — why we came back for the gutters

The homeowner called in week three worried the moss treatment had failed. The roof looked worse — brown, patchy, almost ugly from the street. We told them to wait. That is the hardest part of moss work in Forest Park, where every north slope is under mature big-leaf maple and Douglas fir and the green carpet you lived with for years turns into a brown mess before it ever looks clean.

Six weeks after treatment, we came back for the gutter follow-up. That is when the job actually finishes.

The house

1980s two-story off NW Skyline, tucked into real Forest Park canopy — not “Forest Park area” marketing, actual tree tunnel on the driveway. Composition shingle, north-facing main roof plane, cedar shake on a small garage wing, 140 linear feet of K-style gutter, two stories on the street side.

Moss treatment went on September 28. Gutter follow-up was November 12.

What week six looked like

From the ground the roof still had brown biomass in the valleys — normal for week six per our moss timeline guide. The gutters were the problem:

• Roughly 22 gallons of dead moss, lichen flakes, and roof grit hand-scooped from 140 feet of trough
• Both downspouts on the north side failed a hose test in under 20 seconds — compacted moss mat at the elbows
• Fir needles layered on top of the shed moss, which is typical on these lots; the needles hold moisture and make the mat heavier
• No active green moss on the shingles — the treatment kill was complete, even though the roof still looked rough from the curb

We flushed both downspouts from the top, bagged everything, and ran a second hose test. Full flow in under five seconds on each.

Why the follow-up is not optional

The guide is explicit: schedule gutter cleaning roughly week 4 to 8 after moss treatment. Most dead moss sheds in that window.

Clean too early and you miss the bulk of the material. Wait too long — especially heading into November atmospheric rivers — and you get overflowing gutters full of debris that should have been in a bag, not sitting against fascia paint all winter.

On a Forest Park lot, the shed volume is higher than average. Heavy canopy means heavier moss load to begin with, and the same trees that grew the moss drop needles into the trough while the moss is shedding. You get a double deposit.

What we told the homeowner about the roof

The brown patches on the north plane will continue to shed through normal rain over the next few weeks. We do not pressure-wash a freshly treated roof — that strips granules and voids warranties. Optional gentle hand-brushing on stubborn spots is a month-two-to-six task if anything remains, not a week-six emergency.

We also noted early green specks on the garage shake wing — different material, different moisture hold, worth watching at the next annual inspection. Not a re-treatment trigger yet.

The photo report

Same-day text bundle: gutter before shots, downspout flush video, after shots, and a roof photo from the ladder showing browned but dead moss in the valleys. The homeowner needed documentation for a refinance appraisal — fair request, common on Skyline corridor homes.

If you had moss treatment in the last two months and your gutters have not been touched, check the downspouts before the next three-day rain. Stick a hose in the top opening. If water backs up in 30 seconds, you are not done with the moss job yet.

503-995-1947 to schedule a post-treatment gutter visit — we pair it with moss work across the west hills and Forest Park corridor all season.