My roof is covered in moss. Is that actually a problem?
Honest answer: surface moss is cosmetic, established mats are structural. Here's how to tell which one your roof has and what to do about it.
Surface moss versus established mats
The single most important distinction in Portland roof cleaning conversations is between surface moss (green fuzz visible on shingles, less than 1 inch thick, removable by hand pressure) and established mats (3-4 inches deep, with visible root structure pushing under shingle edges, requires mechanical removal). Surface moss is largely cosmetic. Established mats are structural damage in progress, water gets under lifted shingles, deck rot follows. The two states look superficially similar from the street but represent very different cost and urgency profiles.
The thumbnail test
Walk up to your roof at the eave (most accessible spot). Run your thumbnail across a visible moss patch. If the moss comes away easily with your nail, it's surface-stage and you have months to schedule cleaning. If it has visible root structure that resists thumbnail pressure and seems anchored into the shingle, it's established and the cleaning conversation becomes more urgent because the same root structure is doing damage every day it remains.
Why it matters for cost
Surface moss cleaning is a chemistry-only soft wash, $350-$650 typical for a Portland home. Established mat cleaning requires hand removal first (slow careful work to avoid lifting shingles further), pushing cost to $700-$1,200. The cost difference is real and reflects actual work; established mats genuinely take more crew time and skill.
When to worry beyond cleaning
If moss has been on your roof for 5+ years and you've never had it cleaned, the conversation may have already moved from cleaning to repair or replacement. Indicators that cleaning won't be enough: visible shingle lift at moss mat edges, granule accumulation in gutters significantly worse than surrounding non-mossy areas, interior water stains on ceilings beneath affected areas. If you see any of those, get a roofing contractor (not just cleaning contractor) to assess.
What to do this week
If the thumbnail test shows surface moss: schedule routine cleaning at your next convenient window (2-4 weeks out is fine). If it shows established mats: schedule cleaning within 2-3 weeks before the next significant rain event. If you see lifted shingles or interior staining: get a proper roof inspection first; cleaning may not be the right answer.