On Aug 27, 10:13*pm, Ivan Vegvary wrote:
I own two stud finders and neither is giving me consistent results. *Need to find all of the ceiling joists in my kitchen so I can install 2 light tubes and 18 can lights. *Symmetry is important. *Would like to put in 14" diameter daylight tubes so joist placement is important. *
My problem is that the ceiling consists of 1/2 inch drywall under 1/2 inch plywood. *This is throughout the house and is probably why the stud finders are not consistent. *Complicating this is the fact that the joist are all over the place and not necessarily parallel. *I have a few 13" gaps and a few 17" gaps etc. *I know this from measuring up in the attic. *Further difficulty is that I have about 24" of blown in insulation. *If I had drywall only (you lucky *******s) I would simply go in the attic and shove an awl down along side each joist, and then run chalk-lines down below.. *Can't shove the awl through the plywood! *So I'm working down below on a ladder with a yogurt can attached to my portable drill (wife doesn't like dust) and it takes me about 6-7 holes to locate a single edge of a joist. *Needs to be repeated at the other end which takes just as many tries. *The next joist can be measured out 16 inches and still takes about 5 holes due to irregular placement. *All together I have about 48 locations to do. *Way to slow.

All alternative ideas appreciated. *You're welcome to call me an idiot if it pleases you. *Just help me save some time and effort.

Ivan Vegvary

P.S. *I have about 48 findings not because the kitchen is huge, but because a steel beam runs down the middle of the room below the the ceiling and I cannot run a chalk line through it.

Is the drywall nailed or screwed to the plywood, if screwed, is there
a discernable pattern? Have you tried a bright light shining
parallel to the ceiling right at the ceiling, to show up any nail
heads? Otherwise, a pointy coathanger wire in the end of an electric
drill should go up thru the sheetrock and any reasonble plywood making
for easy drilling and any subsequent patching. Unless this is an
antique farm house, ceiling studs are generally 16" on center due to
building codes and building inspectors.