Clean Freaks Co. Skylight cleaning in Atherton.

An Atherton skylight lives where two problems meet: overhead glazing on a low-slope roof, sitting directly beneath a mature canopy of coast live oak and redwood. Debris does not blow off the way it does from a vertical pane — needles, catkins, oak tassels, and leaf litter collect in the curb, pack into weep channels, and sit against the gasket line. Under the Peninsula’s morning marine layer that debris stays wet for hours, and wet organic litter on glass is how tannin staining, biofilm, and the first green cast of algae begin.

The materials complicate the work. A domed unit may be cast or extruded acrylic, which scratches under grit and hazes under the ammonia and solvent cleaners used on ordinary windows; a flat unit is usually laminated or tempered glass, sometimes carrying a factory low-E or self-cleaning coating that abrasive pads and harsh chemistry will quietly ruin. Around the glazing sit the vulnerable parts — aluminum or clad-wood curbs, EPDM gaskets, flashing, and the condensation gutter and weep holes that keep the assembly dry. These are the pieces that fail when they are scrubbed carelessly or left clogged.

North-facing and shaded slopes are the ones that go wrong first. They dry last after fog and rain, so moss establishes in the gasket seam and algae films the low corners of the glass. Left alone through a wet Peninsula winter, that growth holds moisture against the seals and etches a shadow into the pane that no in-season wash fully lifts — which is why this surface, in this climate, is its own category rather than another pane on the route.

1. The partner identifies each unit before touching it — acrylic dome versus laminated or tempered glass, and whether a low-E or self-cleaning coating is present — and matches pad and chemistry to the material, so acrylic is never hit with ammonia or grit and coated glass is cleaned only with methods that preserve it.
2. Dry canopy debris is cleared from the curb, gasket line, and condensation gutter first, and the weep holes are checked and flushed, so redwood and oak shed is lifted before water turns it into tannin stain and the assembly can actually drain.
3. Moss and algae on shaded, north-facing glazing are treated and lifted rather than scraped — worked out of the gasket seam and glass corners with methods that spare the EPDM and flashing, addressing the growth the fog encourages instead of just the film on top.
4. Glass is finished to a streak-free clarity that reads from directly below, hard-water spotting from irrigation overspray is addressed on the pane, and the curb, flashing, and seals are left dry and clear so the unit is set up to shed the next round of shed and fog.

• Late spring, once oak catkins and pollen have finished dropping — the heaviest canopy shed of the year settles into the curb and gasket line and is best cleared before summer bakes it on.
• Early fall, before the first atmospheric river — clearing leaf litter and clogged weep channels now keeps the wet season from pooling water against the seals.
• Late winter into early spring — after months of marine layer and rain, moss and algae are at their peak on north-facing glazing and should be lifted before growth etches the pane.
• After any prolonged marine-layer stretch — when mornings have stayed damp for days and the shaded skylights start reading green or hazy from below.
• Following tree work or a winter storm — when a redwood or oak has dropped a fresh load of debris across the roof glazing.