FLAT TILE
ROOF WASH.

CONCRETE TILE
IN CUPERTINO.

Flat concrete tile is one of the most common roofing materials in Cupertino — and one of the most misunderstood when it comes to cleaning. The porous surface of concrete tile retains moisture longer than glazed or sealed tile types, which makes it especially prone to moss, lichen, and algae growth in the Bay Area's fog and morning dew cycle. North-facing sections and areas shaded by mature trees accumulate growth fastest — and once lichen is established, it holds moisture against the tile surface even in dry conditions.

> Why flat concrete tile cannot be pressure washed

High-pressure washing cracks and chips flat concrete tile, displaces mortar at ridgelines and hips, and forces water beneath tile edges where the underlayment sits. The correct method is soft wash — low-pressure application of a biodegradable treatment solution that kills biological growth at the root. The solution does the work, not the pressure. Tile surface and mortar are left intact.

> What Cupertino fog does to roofs

Cupertino's position at the base of the Santa Cruz Mountains means regular morning fog that keeps roof surfaces damp through mid-morning. Combined with the city's mature residential tree canopy — particularly on the western hillside streets — this creates persistent biological pressure on flat concrete tile. Roofs left uncleaned for several years can develop dense moss and lichen coverage that accelerates tile degradation.