Why should an inspector be cautious about walking a roof in the early morning?

Dew forms overnight on a roof surface that has radiated its heat to the sky, and on a sloped surface a thin film of water is enough to eliminate the friction that walking depends on. The hazard is worse than it looks: the surface appears merely damp, the roof is one an inspector has walked dozens of times before, and the loss of grip is sudden rather than gradual. Asphalt shingles hold dew particularly well, and metal and tile become genuinely dangerous. Frost is the same problem in a more visible form. The professional response is to wait for the sun to dry the surface, or to decline the walk and inspect from a ladder at the eaves, from the ground with binoculars, or from a drone — and then to state in the report that the roof was not walked and why. Inspector safety is a legitimate reason to limit the inspection, provided the limitation is reported.

Dew leaves a water film on the slope that removes the friction walking depends on, and the resulting loss of grip is sudden rather than progressive.

Inspectors walk roofs only where it is safe to do so. Dew, frost, moss, steep pitch and fragile coverings are grounds for inspecting from a ladder, from the ground or by drone, with the limitation reported.

Wet Slope, No Grip. A film of dew looks like nothing and behaves like ice.

Moss and algae keep a slope slippery long after dew has dried, and are common on north-facing and shaded slopes.

• •Walking a dewy roof because it has been walked safely before
• •Declining the walk without reporting the limitation
• •Overlooking moss and algae as ongoing slip hazards