Q. This spot appeared over a year ago in the northeast corner of my garage ceiling. It has stayed the same size and hasn’t changed at all. What is it, and what should I do about it?

A. From its splotchy appearance, the spot is more than likely mold. Your ceiling drywall apparently got wet and stayed damp long enough for mold to grow. Since the spot hasn’t grown, chances are this was a one-time occurrence, perhaps from a hard rainstorm or an ice dam.

You could try to clean it with a strong detergent mix with water (no bleach), but drywall is difficult to clean and the damage looks too extensive. I’d cut out the damaged section and replace it only after you’ve found and corrected the problem. Opening the area also allows you to check for additional moisture as well as investigate the cause.

If you can’t narrow the cause to a single event, like a driving rainstorm or a thaw after a heavy snowfall (ice dam weather), check the area directly above the damaged area, either the roof or an exterior wall (if you have a second story) for potential water entry points. Look for gaps in flashing around plumbing vents, dormers, chimneys or other roof penetrations, gaps between trim and siding, a window with a rotted sill, damaged shingles or other noticeable flaws. Or if you have an attic directly above the garage, go up there with a flashlight and look for telltale water stains running down the roof sheathing or rafters. There are many potential fixes; finding the cause is usually the toughest part.