Roofing contractors know what a magnet roofs can be for the random debris of society — and it often gets to ferment for several months before anyone notices. Keeping roofs more than clean is something that keeps some scientists up at night. The recent annual meeting of the Reflective Roof Coatings Institute showed how complicated life on the roof can be.

“I find life where we don’t want it,” said Susan Pfiffner, an associate professor with the University of Tennessee. She is one of many professionals dedicated to microbial control in modern buildings.