30 July 2026

Did you know your roof pitch helps determine how fast panels get dirty?

On a steep roof, rain rinses away most of the loose dirt itself: on a flat setup it stays put.

Water is lazy: it follows the slope. On a steeply pitched panel, rainwater runs down quickly and carries loose dust and pollen with it: a free pre-rinse with every shower. The steeper the panel, the stronger that self-cleaning effect: and the longer the panels keep looking clean.

On a flat or gently sloped setup, such as panels on frames on a flat roof, the opposite happens. The water flows slowly, lingers along the bottom edge of the panel and evaporates there: the dirt it carried stays behind as an edge along the frame. That edge is exactly what you see first on flat setups, and rain will not remove it: static grime, algae and droppings only come off with a brush.

Mind you: surroundings weigh heavier than the angle. Trees nearby (pollen and leaf haze), a coastal location (salt haze that rain does not dissolve) or many birds will soil even a steep roof faster than a flat setup in an open polder.

The practical translation: steep roof in an open, clean environment: one cleaning visit in spring is often enough. Flat setup, coastal location or lots of greenery: plan two a year, and then a cleaning subscription at € 65 to € 140 per visit on a yearly contract is cheaper per visit than separate bookings. The full rates are in the price index.