Roof Maintenance: What Actually Matters Around Here

Roof maintenance is two things: getting the debris off, and dealing with what's growing up there before it lifts your shingles. Twice a year is the standard recommendation, and under heavy fir cover it's often more. Most of what follows is the part the roofing companies leave out — none of the pages I read before writing this listed a price, and none told you when maintenance stops being worth doing.

If you're here because a home inspector flagged moss on a four or five year old roof — the most common version of this question locally — the short answer is that it depends on whether it's moss or algae, and how far in it's got. Light growth on a young roof is a treatment, not an emergency.

What Roof Maintenance Actually Covers

The National Roofing Contractors Association recommends inspecting your roof "at least twice per year, preferably in the spring and fall," plus after severe weather. The core task, in their words: "debris such as leaves or other foreign materials that have accumulated on the roof should be removed" — with particular attention to valleys, gutters and roof drains, where buildup restricts drainage.

That's the whole mechanism. Debris doesn't damage a roof by sitting on it. It damages a roof by holding water somewhere water was supposed to leave.

A roofing contractor named Nicholas Riley described debris trapped in a roof valley leaking through the underlayment into the decking and drywall. The repair came to $6,300. His summary: "$6,300 could have been saved by simply cleaning off the leaves from his roof."

Moss vs. Algae: Only One Is a Real Problem

This is the distinction almost nobody local explains, and it changes what you should worry about.

The black streaking is algae — Gloeocapsa magma. The Asphalt Roofing Manufacturers Association notes this discoloration "has been most widespread in the Gulf States and along the Northwest and Eastern Seaboards," so yes, us. Owens Corning, who make the shingles, are blunt about what it does: the company "has not seen evidence that algae deposits affect the performance of asphalt shingles. Algae, or streaking, is more of an aesthetic problem and may impact the look or curb appeal of your home."

Moss is the actual problem. Owens Corning separates it out: "green algae (typically green in appearance) or moss sometimes found on roofs with northern exposure, overhangs or high moisture areas, is not the same species." Moss is a plant. It lifts shingle edges, holds water underneath, and that's where leaks start. GAF notes algae grows "on the northern exposures of the roof since this exposure generally receives less sunlight," and that dew, not rain, is the primary moisture source. You can check your own north slope from the driveway.

Why it's so bad here comes down to timing rather than volume. NOAA's current normals for the McMillin Reservoir station in Pierce County show 45.13 inches of rain across 166 days a year — and about 72% of it falls October through March, in the cool months when a north slope never dries out. July and August together bring 1.82 inches. Sea-Tac, the station everyone quotes, shows 39.34 inches across 156 days, so south Pierce County gets nearly six inches more rain and ten more wet days than the airport figure suggests.

Jay Pscheidt, a plant pathologist with Oregon State University Extension, put the maintenance reality better than I could: "You can clean all you want but to keep moss at bay, the environment needs to change. You've got to let the sun in or it will return." Overhanging branches are the fix more often than chemistry is — and that's also why zinc strips underperform here, since research cited by Oregon State puts their effect at about 15 feet downslope and plenty of local roofs grow moss with strips installed. For the full mechanism, and the detail on zinc and moss treatments, see why moss on a roof is a structural problem and not a looks problem.

Is Pressure Washing a Roof Safe?

You'll find plenty of writing that says never pressure wash a roof. I pressure wash roofs. So here's the real version.

ARMA says, in full: "High pressure washing systems are likely to damage asphalt roofing and should not be used on asphalt roofing for removing algae or for any other purpose." GAF names the failure mode: "Do not power wash the shingles to clean the shingles... it is not recommended as it may dislodge granules, which can lead to premature shingle failure."

Now notice what those same documents prescribe instead: a bleach and water solution, left 15 to 20 minutes, then "rinse the solution from the roof by gently spraying the surface with water," and "avoid scrubbing the surface, as this friction may loosen and remove granules." That is a soft wash. Chemistry does the work; water carries it away.

So the honest answer: what wrecks roofs is impact force at the surface, which is pressure and fan angle and distance. The people who damage roofs never think about the last two. I work at low pressure with the chemistry doing the lifting, which is what those bulletins describe. If someone quotes you a roof wash without mentioning method, ask.

What It Costs Around Here

• A Tukwila-area company lists one-time roof cleaning starting at $549, and an annual cleaning-and-maintenance program starting at $329 for one to two visits
• An Everett company quotes $350-700 for a roof blow, hand gutter clean and moss soft-wash on a 2,000 sq ft two-story house
• A Tacoma soft-wash outfit puts roof cleaning at $300-800 depending on size, moss and access

Note the pattern: an annual program costs less per visit than one-off calls. Not a sales trick — a roof cleaned last year takes less time than one with four years of growth on it. If you're pricing other exterior work too, here's what power washing runs in this area and what gutter cleaning costs.

When It Isn't Worth Doing

The NAHB puts the service life of an asphalt shingle roof at around 20 years. If yours is at 18 or 19, cleaning it is money spent on an asset that's leaving. It'll look better. It will not buy you five more years.

Second case, counterintuitive: moss that has rooted into the shingle gaps can be worse to remove than to leave. Pulling it out can take the seal with it, and a roof that wasn't leaking before starts leaking after. If growth is that established on an older roof, plan the replacement and keep the gutters clear until then.

And if what you have is black streaking on a south slope and nothing else — that's algae, cosmetic by the manufacturer's own account, and you're allowed to not care. Plenty of people do, because curb appeal is real. Just book it knowing it's a looks job, not a protection job.

Where I'd tell you to call someone else: active leaking, flashing damage or missing shingles is a roofer's job, not a cleaning job. I'm a licensed general contractor and I'll tell you honestly what I see up there, but a failing roof needs repair before it needs washing.

Frequently Asked Questions

How often should a roof be maintained? At least twice a year, spring and fall, per NRCA guidance, plus after severe weather. Under heavy conifer cover here, more often — needle drop isn't seasonal the way leaf drop is.

Is pressure washing safe for my roof? High pressure is not — it knocks granules off and shortens shingle life. Controlled low pressure with the cleaning solution doing the work is the correct method, and it's what the manufacturer bulletins describe. Ask what pressure and what tip.

Should I get up there myself? I would rather you did not. BLS data for 2023 recorded 110 deaths among roofing contractors, and Washington triggers fall protection at four feet where federal OSHA says six. A bleach-treated roof also turns slippery. You can learn most of what you need from the ground with binoculars, and if you would rather not go up at all, there are tools that work from the ground.

Do the black streaks mean damage? Usually no. That's algae, and Owens Corning states it has seen no evidence it affects shingle performance. Moss is the one that causes real damage.

Will insurance cover damage from neglect? Generally not. As Janet Ruiz of the Insurance Information Institute puts it, insurance "is designed to protect against sudden and accidental losses rather than damage that results from ongoing neglect."

Want someone to look at your roof and tell you straight whether it needs cleaning, repair, or nothing at all? See the roof cleaning and treatment service or reach out for a free estimate. I handle most of every job myself, so the person who looks at it is the person who does the work.

Sources: National Roofing Contractors Association, Asphalt Roofing Manufacturers Association, Owens Corning, GAF, Oregon State University Extension (Jay Pscheidt), University of Washington Miller Library, NOAA National Centers for Environmental Information (1991–2020 Climate Normals), U.S. Bureau of Labor Statistics, Washington State Department of Labor & Industries, Insurance Information Institute, NAHB, Valentine Roofing, Chinook Services, Softwash Tacoma, Homeyou.