The short answer to the question "What causes vinyl siding to melt?" is that it's sunlight. But it's not sunlight shining down from above, it's the light that bounces off windows and onto the vinyl walls. And not just any windows either. So called distortion, the melting and buckling of vinyl siding, is caused by solar beams bouncing off energy efficient low-e windows that have a highly reflective surface and often a concavity that makes them act like lenses, focusing hot sunshine right onto the siding nearby.
Does vinyl distortion happen only in the summer, or only in hot climates?
We have lots of customers who come to us asking for help with vinyl siding melted by sun reflections who can't believe it happened to them. They thought sunlight reflections could never be hot enough to melt their siding in winter, or in their cooler climate, but the fact is sunshine reflected and concentrated by low-e windows can get hot enough to melt vinyl in all seasons and in most places in the world.
Will the heat created by reflected sunlight set my siding on fire?
No need to worry about your siding igniting and burning, that takes heat greater than 730º Fahrenheit. But to stop that siding melted by window glare, get Turf Guard Window Film and send the light scattering harmlessly instead of concentrating damagingly. This exterior window film will stop melted siding, damaged turf grass, and unpleasant reflections immediately.