Roof washing on Sanibel Island.

Sanibel roofs take a combination that is hard to find anywhere else: the heaviest daily salt on this coast, island humidity that never drops, and the dense conservation-minded canopy that keeps most lots shaded. Metal is the common roofing here for good reason, and while metal handles the salt better than most materials, it still holds algae in the shaded runs and the salt still works at the fasteners and flashings underneath.

Our roof washing uses a solution that kills the growth at the root and a low-pressure rinse that carries the salt film off with it. Pressure is emphatically wrong on a standing-seam roof — it drives water under the panel seams and lifts the sealant at the ridge, which on an island home is a leak in the next storm.

Runoff is handled with the island's conservation rules in mind: solution at working dilution, plantings and buffers pre-wet, everything rinsed down behind us so nothing reaches wetland. Where the siding and soffits below have gone the same way, soft washing is the matching job. More on the island in Sanibel.