It happens every year.

I ignore it as long as I can, pretending I’m on an alternative architecture tour admiring a living roof.

Lush, verdant, it’s a little meadow that harvests rainwater and contributes oxygen to the atmosphere. But really that green isn’t supposed to be up there. Time to clean the roof.

Our house has a small footprint, but the roof is complex and steep. When we calculate roof runoff, the area is a modest 1000 square feet, but when we go to clean the surface, the monster hulks out to a staggering 3,000. I’ve never signed on to scrub that much of anything, let alone something canted at 45 degrees and looming 30 feet off the ground. But moss must be removed, so eventually I found myself tiptoeing off the top rung of a ladder, stretched out full length against the shingles, hands clenched in death grips on rope and scrub brush.

There’s something zen-like about picking clumps of moss from between thousands of shingles, and scrubbing green threads off the gritty surface holds an addictive charm. The appeal waned quickly though and my entire body ached. I did feel the glow of accomplishment — or maybe it was relief at surviving the ordeal — but I didn’t look forward to another bout.

There will come a day when I won’t be able to go on the roof even if I want to. Then I’ll throw money at the problem. For now though, I’m in do-it-yourself mode, therefore I’ve investigated all the magical products and methods that are supposed to effortlessly rid my roof of moss.

Zinc strips seem the automatic choice. They’re good from a safety standpoint — you only have to go up the ladder and clamber around on the roof every few years. Supposedly you just tack the things in place on each side of every ridge and the chemical reaction does the rest.

Unfortunately for all who care about the health of Puget Sound, zinc knocks off more than moss.

According to the Washington Toxics Coalition, “Zinc is potentially toxic to fish and other aquatic life. If you install zinc strips or zinc-impregnated composition roofing, make sure that roof runoff doesn’t flow directly into storm drains, streams or other bodies of water. If you collect water from your roof in rain barrels, you may want to avoid using the water for your vegetable garden. Copper strips and copper-impregnated shingles should be avoided due to copper’s toxicity: copper is roughly 10-25 times more toxic to aquatic life than zinc.”

The city of Amsterdam is removing all zinc and copper from its historic roofs and downspouts — at great expense. That’s how bad zinc is for marine life.

When installing zinc strips, or the new metal-impregnated shingles, you’ll need to disconnect any downspouts that go over the bank into Puget Sound, a drainage ditch, stream or lake. The water can be directed into rain gardens and other infiltration areas instead.

Next on the ease scale is moss-killing treatment.

The actual application isn’t necessarily easy. You still have to climb around with a bag of powder or a squirt bottle and evenly cover the entire surface of the roof. There are several such products on the market. Avoid those that contain zinc or copper crystals.

Some folks use laundry detergent.

I tried that once and the white powder sat up there for weeks. Esthetically, white clumps weren’t an improvement over the green clumps of the moss itself, and I wondered what effect detergent, which is supposed to dissolve oily stains, might have on shingles made of oil. Some roofers recommend bleach, while others say it makes shingles harden and crack, hastening the need for replacement.

But the real reason not to use laundry detergent is chemical runoff. Most brands contain phosphates and chlorine; weapons of mass destruction to marine life. Phosphates feed algal blooms that deplete oxygen and suffocate fish. Chlorine, used for killing microbes in swimming pools, can also kill plankton. Other ingredients coat gills, preventing fish from taking in oxygen.

This guilt trip won’t stop the use of products that chemical companies advertise as a panacea. But if you take that bag up on the roof, first do the Sound one small favor: disconnect the downspouts from the drains that flow into the bay. Let the water run onto nearby plants (which will likely provide a nice object lesson by getting sick) or collect the rinse water in buckets and use it to water the lawn where it can filter down through the soil before working its way back to the water supply.

Even if a moss killer works, even if it’s completely nontoxic to humans, fish, plants, microorganisms and the man in the moon, even if we disconnect downspouts, whether the roof is metal, shake, tile or fiberglass, there is still one more job to do. Somebody must get up there and remove the carcasses. There are a number of methods for that task as well — scrubbing, sweeping, compressed air and pressure washing. For metal roofs there’s even a nifty machine that runs up and down the channels.

And, whether doing it yourself or outsourcing, whoever goes up on the roof needs a lifeline or harness. There shall be no unprotected sweeping.

Pressure washing is controversial. Some roofers swear by it, others say it forces water up under shingles, leading to rot. Air pressure can degrade asphalt by blowing away those little granules that add color, protect the tarry stuff from sunlight and provide some traction to anyone fool enough to walk around on the roof. (There shall be no golf cleats either.) Any method of physical moss removal will remove granules, which those picky roofers insist are needed on the roof rather than in the gutters.

The gentlest method is elbow grease, aided by a scrub brush, a broom and some kind of narrow plastic implement to get between the shingles.

Moss removal is tough. Have a cold drink ready for the end of the day. Enlist somebody cute to massage your shoulders. And, whatever material your roof is, if you value its watershed capabilities resist the temptation that will seize you at least once during the project to wield the scrub brush as a cudgel and pound the moss to dust.

Since plants are determined to grow on my roof, I’m thinking of installing a living roof when the shingles wear out. Oh the irony — bet I end up planting it with moss.

Washington Toxics Coalition — www.watoxics.org; Puget Sound Partnership — www.psp.wa.gov; green roof information — www.epa.gov/hiri/strategies/greenroofs.html.