Ceiling joist location help, (stud finding)

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 bastards) 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.
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wrote:

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.

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 bastards) 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. Alltogether

Since you can get to the top side, instead of an Awl to make the marking holes, use a drill.
I'd try the magnet idea first, though.

steel beam runs down the middle of the room below the the ceiling and I cannot run a chalk line through it.
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The drill idea from above seems the fastest and surest. As suggested further down I could get an electricians long bit and thereby be able to tuck up adjacent to the joist.
Thanks, Ivan Vegvary
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wrote:

down I could get an electricians long bit and thereby be able to tuck up adjacent to the joist. Just remember which side of the joist you drill on. ;-) My suggestion is to remember N/S, or E/W, or perhaps "on the driveway side" (not L/R).
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On 8/27/2011 11:13 PM, Ivan Vegvary wrote:

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.

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 bastards) 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.

steel beam runs down the middle of the room below the the ceiling and I cannot run a chalk line through it. 1. Get a piece of steel bar stock, say a couple feet long, and shove it down through the insulation and lay it beside the joist, up tight against it. That should give enough of a mass for your stud finders to give a good reading. If not, borrow/buy/rent a low-end metal detector. It'll hit on it. Or like the other guy said, some high-strength magnets. Two points a couple feet apart will be enough to plot that joist across the whole room.
2. Go look at the laser levels, including the spinning ones. Some also work mounted sideways, and could 'paint' a line on both sides of a beam from a tripod centered below the beam. The cheap alternative that I would use for a single project is a small framing square , to make witness marks on either side of beam, and carry them around the beam. Do your joists run across the beam, or are they lapped there? Projects like this are where high school geometry comes in handy.
3. For the solatubes, drill pilot holes up from below, and shove a piece of piano wire straight up, and measure how far you are from nearest joist. The tubes do not have to be straight up and down. Adjust your layout till you find spots that are pleasing to the eye from below, and clear the joists. Any pilot holes that are too far off will be easy to patch with a dab of putty- you are gonna end up painting the ceiling anyway.
4. Having said all that, I would be hesitant to put that many holes in an insulated ceiling. You do know all the lights will need the special shrouds above them, and will still be heat loss points, right? I'd be much more inclined to use pancake boxes recessed into the drywall and screwed to the plywood, and use shallow surface-mounted cans, or even puck lights. It'd still be a PITA daisy-chaining the lights through that sea of insulation, but a lot less work than 20 big holes with drifts of insulation coming down.
--
aem sends...

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SURELY in these days, CFL'S will be used, and venting requirements based on incandescents would not be applicable. But the units still have their "Maximum 60 watts" stickers. Or more. I would like to see replacement stickers that would be put over that would say "Maximum 14 watts" or whatever.
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On 8/28/2011 6:37 AM, Michael B wrote:

Unless code has been changed, the requirement still exists. Next owner may not like CFLs, and put old-style bulbs in there. Now if he went with something exotic where regular bulbs would not fit, it might be different.
--
aem sends...

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I like the bar stock idea. Have plenty of 5/8" square tubing on hand along with short pieces of 3/4" pipe. More aluring however, is your idea of using 'puck lights'. We didn't want too much of projection into the room (e.g. track lights) but I will look for lights that are minimally invasive.
Thank you, Ivan Vegvary
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On 8/27/2011 10:13 PM, Ivan Vegvary wrote:

light tubes and 18 can lights. Symmetry is important. Would like to put in 14" diameter daylight tubes so joist placement is important.

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 bastards) 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! ...
A) Bell-installer bit (or use an extension bit holder) and drill along the joists from the attic; nothing says you have to be able to punch the hold manually.
B) Measure (consistently) from one end to other in the attic the location of each joist and transfer the measurements to below.
C) Just place openings where want them from function and aesthetics and deal with it as needs be by boxing any joists that do need it after the fact...
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An electrician's bit and working from above might be the fastest. Miserable conditions up there. Vertical clearances are as low as 8". Additionally, half of the kitchen has a double roof over the ceiling. There has been an addition done and instead of removing the old roof they simply build another one above. W(Out West this method is called a 'California Roof').
Anyway, drilling from above and accurately measuring and diagramming from the attic should save a lot of time.
Thanks, Ivan Vegvary
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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 bastards) 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.
Long thin drill bits no more than 1/8" wide by up to 2 foot long are sold. A heavy wire coat hanger cut with pliers to a point works almost as well even through wood.
I would pick a central or important location and find the ends of that rafter. Careful measuring in the attic, transferred to masking tape on the ceiling below will get you within 3/4" of the location of the remaining joists. Another 1/8" hole can be drilled at each penetration point for confirmation.
1/8" holes in any material are easy to fill.
--
Colbyt
Please come visit http://www.househomerepair.com
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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.
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tear down the cieling for maximum symmetry placement.
otherwise you are just screwing around and theres a big likelyhood of unknown obstructions:(
like water sewer fireblocks joists at wierd spots etc etc. or go with surface mounted fluroscent fixtures that will be easier to adjust location of.....
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