Locate the attic access or remove a ceiling light fixture cover
Use a stud finder set to detect joists
Tap the ceiling and listen for solid, dull sounds
Measure from a known wall or joist spacing pattern
Look for nail pops, seams, or fastener lines in the ceiling
Check from above in the attic for parallel framing members
Use a small drill bit or awl to probe carefully
Confirm joist direction by finding multiple solid points in a line
Mark the joist locations with painter’s tape or pencil
Verify spacing, usually 16 or 24 inches on center