Just as wall studs support shelving or heavy decor, the beams in your ceiling can support new light fixtures, fans or decorations. Unless they are exposed as architecture details, structural ceiling beams -- called joists -- are hidden by paint and plaster. Joists are usually spaced at the same intervals as studs -- 16 or 24 inches apart. If your ceiling is flat and of a consistent density, a stud finder is your best bet; if you have a popcorn ceiling or other embellishments, you might have to resort to more complicated options.
Stand on a ladder near one of the side walls of the room. Hold a stud finder up to the ceiling a few inches from the wall and calibrate it according to the manufacturer's instructions.
Measure 16 inches in from the wall with a measuring tape. Run the stud finder over the ceiling in that area. When it lights up, it has reached the edge of a joist. If it doesn't find a joist, measure 24 inches from the wall and try that area instead.
Note whether the first joist was 16 or 24 inches from the wall. Measure the same distance away from that joist to find the next one. Run the stud finder over the area to ensure you're in exactly the right place. Continue all the way across the ceiling.
Hold a flashlight right by the ceiling on a very gentle angle to the surface, so the light shines nearly horizontally across it. Look for dimples in the paint. They usually indicate the presence of a nail behind the plaster, and where there's a nail, there's a joist.
Hammer a small nail into a popcorn ceiling 16 inches in from the wall to test for a joist. Stud finders measure density to find beams, so they don't work on popcorn ceilings. If your nail penetrates the ceiling and doesn't hit a solid surface, check again an inch away; if you don't find one there either, measure 24 inches in from the wall and check there instead.
Things You Will Need
- Measuring tape
- Stud finder
- Nail and hammer
- Calibrate your stud finder against an area of the ceiling where you don't expect to find a joist, so its base density reading is for a hollow area, not a solid one.
- Wear a dust mask if you have to hammer a nail into the ceiling repeatedly, especially if your ceiling is covered in any kind of embellishment or plaster that releases dust.
- If you don't find a joist at 16 or 24 inches in from the wall, the beams might run across the room the other way. Try measuring in from a perpendicular wall instead.
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