The national rule of thumb is "every few years." On the Peninsula that's too vague to be useful, because microclimates here vary block by block. We set a cleaning interval based on three things we can see from your roof.
1. How much fog and moisture the roof gets
Pacifica, Daly City, Colma, Half Moon Bay and the western half of San Francisco sit in the marine layer most of the year. North- and east-facing slopes in those areas rarely dry out, and moss can go from a few patches to a carpet in two seasons. Expect a two-year interval there. Burlingame, San Mateo, Belmont and San Carlos east of the hills get more sun and usually go three to four years. Foster City and Redwood Shores, flat and windy, often go longer.
2. What's growing over the roof
Redwoods drop needles constantly. Oaks drop leaves and acorns. Eucalyptus drops bark and oil-rich leaves. All of it collects in valleys, behind chimneys and against skylights, holds water, and seeds moss and lichen. A roof under heavy canopy in Woodside, Portola Valley, Menlo Park or Burlingame's Easton Addition may need debris removal every year and a full soft wash every two to three.
3. What the roof is made of
Composition shingle shows algae streaking first and holds moss in the overlaps. Concrete and clay tile grow lichen on the shaded faces and moss in the channels. Wood shake is the most vulnerable and should never carry moss for long. Metal roofs resist growth but still collect debris and algae film on low-slope sections.
Fox puts your cleaning interval in writing
When we finish a cleaning we tell you when we'd expect to see you again, based on what your roof actually showed, and we put it in writing. If your insurer has been reviewing roofs in your area, we also recommend keeping dated photos on file every year. It costs nothing and makes any future letter a five-minute problem.
Not sure where your roof falls? Send us a couple of photos and we'll tell you.
Fox Roof Cleaning wrote 2 related guides
Fox Roof Cleaning also explains Your insurer sent a roof letter. Here's what to do, and what to send back and Soft washing vs. pressure washing a roof: why manufacturers only approve one.
See all 6 Fox roof cleaning services or insurance-required roof cleaning.
Published by Fox Roof Cleaning, Millbrae, CA.