The short version. Moss is treated on a dry day between October and May. That is a long season, and it is the dry stretch rather than the month that matters — the product needs to go down dry and then be carried through the moss by the rain that follows. Late winter and spring is when the results show fastest, because the moss is at full growth and dies back visibly.
What matters more than the calendar is which stage your roof is at. Two of the five need nothing at all. One of them should not wait for spring.
There is a second question worth asking in Lakewood, because almost every roof here drains toward a lake. More on that below.
Call (253) 366-8066 and we’ll connect you with a licensed local specialist who works Lakewood.
Why Lakewood roofs, specifically
the median year a Lakewood detached home was built. 40% of the city went up in the 1940s and 50s alone.
Pierce County Assessor, Aug 2026of Lakewood’s 12,701 detached homes have a roof moss grows on.
Pierce County Assessor, Aug 2026of those roofs are on homes built before 1990 — 85%, against 54% for Pierce County as a whole.
Pierce County Assessor, Aug 2026lakes whose water quality the city actively manages — American and Waughop — with a lake district advisory committee on one of them.
City of LakewoodMoss does not need a bad roof. It needs shade, moisture and something to hold onto, and Lakewood supplies all three. What makes the city unusual is how much of it went up at once: the post-war decade put more than five thousand houses on the ground here, and the streets planted around them closed over a generation ago.
Every single-family detached home in the city, from the county tax roll. Seven predate 1900 and are left off the scale. Hover any bar for the count.
One decade dominates everything. The 1950s alone put up 3,723 of Lakewood’s detached homes — nearly three in every ten standing in the city today — with the 1940s and 1960s bracketing it on either side. Lakewood is a post-war city, and its roofs are all coming of age together.
What a treatment actually is
Not a wash. The standard product is a zinc sulfate powder or granule, applied dry along the ridge and upper courses, which then works down the slope with the rain over the following weeks. It kills the moss where it sits and leaves a residue that discourages regrowth for a season or two.
The label sets the rate, and the county tells us the roof size, so the quantity for a typical Lakewood house is arithmetic rather than guesswork. EPA Reg. No. 10699-1 specifies 3 lb per 600 sq ft on a pitched roof, and the median pre-1990 Lakewood roof footprint is 1,369 sq ft — a third bigger than Tacoma’s.
| Roof pitch | Surface area | Zinc sulfate |
|---|---|---|
| Footprint only (flat proxy) | 1,369 sq ft | 6.8 lb |
| Low pitch, about 4:12 | 1,574 sq ft | 7.9 lb |
| Steeper, about 8:12 | 1,780 sq ft | 8.9 lb |
Footprint is recorded floor area divided by story count, across 9,833 pre-1990 Lakewood homes with a moss-susceptible roof. The pitch multipliers are standard geometry. This is an order of magnitude with the arithmetic shown — not a quote.
It is useful mostly as a sanity check. A treatment for a house this size is a small quantity of product and a couple of hours of careful work on a ladder; most of what you are paying for is the access, the care taken not to damage the granules, and the fact that whoever is doing it is licensed to apply it at all.
The question that matters here: where does the runoff go
The standard moss product is zinc sulfate, and it does not stay on the roof. It works down the slope with the rain, into the gutter, down the downspout, and then wherever your downspout points — which in most of Lakewood is a storm drain, and a storm drain here does not lead to a treatment plant. It leads to a lake.
Zinc is toxic to fish. That is not a fringe position: the regional stormwater program run by Puget Sound municipalities advises removing moss by hand where possible, disconnecting downspouts before any roof treatment, and diverting the runoff onto ground rather than into the storm system. Lakewood is a city named for its lakes, and it actively manages the water quality of two of them.
The license behind the work
Washington law treats your roof as “land.” The Pesticide Application Act defines land broadly enough to include a structure, which puts moss treatment squarely inside it — so applying a moss killer on someone else’s roof for money is a commercial pesticide application, and it requires a WSDA commercial applicator license carrying the Structural and Turf category. It is a small, specialized trade, and every specialist we connect you with holds it — checked against the register before we pass along your details, so the licensing is simply taken care of.
- Licensed applicator, with the category that covers roofs — every specialist we refer holds it
- Debris and needles cleared first, by hand, so the product reaches the shingle
- Dry product along the ridge and upper courses, not a pressure wash
- Downspouts disconnected or diverted before the product goes on, so the runoff does not reach a storm drain
- Gutters and downspouts flushed afterwards, so nothing sits in the trough
- Plants below protected — zinc sulfate runoff is hard on what it lands in
- Realistic expectations set — moss goes brown and washes off over weeks, it does not disappear the same afternoon
The one thing not to do
Do not let anyone pressure-wash an asphalt shingle roof. The granules on the surface are the roof’s ultraviolet protection and they are held on with asphalt, not glue — a pressure washer takes them off, and a roof stripped of granules ages far faster than one with moss on it.
Every shingle manufacturer says the same thing, and the specialists we work with treat it as settled: on composition shingle, soft methods only. It is one more thing you do not have to think about when the introduction comes through us.
Where we work in Lakewood
Across the city, with the older lakeside neighborhoods and the post-war streets around them the ones that need it most often.
Find out which stage your roof is at
Tell us your neighborhood and what is above the roof, and send a photo from the driveway if you have one. We will tell you whether it needs treating this spring or can wait — and if it needs work, connect you with a licensed local specialist who works Lakewood. No cost to you, no obligation.
Call (253) 366-8066Get a Free Quote Cascade Roof & Gutter is not a contractor and does not perform work. We connect Pierce County homeowners with independent licensed specialists.Nearby
We cover the whole of Pierce County. If you are closer to one of these, start there:
Sources
- Pierce County Assessor-Treasurer, improvement_builtas and tax_account extracts, August 2026, joined on parcel number — 12,701 Lakewood single-family detached homes, roof cover, year built and floor area.
- Pierce County 2025 Tax Rates for Incorporated and Unincorporated Areas — tax code area to city mapping.
- RCW 17.21, Washington Pesticide Application Act — definitions of “land” and “pesticide,” and the commercial applicator licensing requirement at RCW 17.21.070.
- Washington State Department of Agriculture, commercial applicator license register — Structural and Turf, demossing, Pierce County.
- EPA Reg. No. 10699-1 — zinc sulfate monohydrate, application rate for pitched roofs.
- PNW733, Managing Moss on Roofs — WSU / OSU / University of Idaho Extension.
- City of Lakewood, Lake Management — American Lake and Waughop Lake water quality programs and the American Lake Management District advisory committee.
- Puget Sound Starts Here — regional stormwater education program: roof moss removal and stormwater guidance.