Kevin, let's start over; I don't think Sonic intended his post quite as strong as you must have taken it, he was mainly trying to point you to a span calculator; but it's easy, after dealing with this sort of stuff as long as he has (at least 6 years working on his own studio) to forget what it's like to enter into a new subject and not know enough about it to even ask the right questions
We're not here to make people feel bad (although in extreme cases of laziness I've been known to get a bit gruff myself
) and I know how easy it is to be maybe a bit too sensitive or embarrassed by lack of knowledge, but stick with us - you won't be sorry in the long run.
Remember, we all started out knowing NOTHING so there's nothing to be defensive about - Before long, you'll be helping others with your newfound knowledge, as well as enjoying your new, quieter, better-sounding space...
Now, on to your question -
16"h floor joist 15" off center no support poles.
Joist span 23' across.
Question:How do I find out if this ceiling will support 2 layers of 5/8
drywall?
By this, do you mean your floor joists are 16" tall? Can I assume that these are then some sort of manufactured joist, like a TrusJoist or similar, where the bottom and top are larger solid wood and the center is blotchy-looking wood (called OSB) ?
If that's what you have, then a normal span table can't help you; instead, you would need to find the exact manufacturer info on those joists to see what they can support - there should be some sort of identifying marks on the joists themselves, telling what company made them, what the part number is, probably even the date they were made; you would then need to contact the manufacturer and ask what those joists, which are probably on 16" centers (this is a standard in the building industry - it's measured from center to center, or from leading edge to leading edge) can support.
This value would be stated in PSF, which stands for Pounds per Square Foot - there will be a Live load rating and a Dead load rating, typically expressed as 50/20, the Live load being first.
Dead load ratings INCLUDE the weight of the framing, so you would need to know how much your joist weigh per foot also; from that info, we can help you figure out what can be added safely.
Or, if you end up talking to the people who built your house, they may be able to tell you what your floor is rated at and how much you can add - 5/8" gypsum wallboard weighs about 2.5 pounds per square foot, so a double layer would add 5 PSF to your construction; standard house insulation (the fluffy fiberglass) will add just under another pound per square foot with R38 batts in place.
If my earlier post helped you figure out how to add pix, a shot or two of your situation will help the discussion along. If there's any markings on your joists, a close-up shot of that may make things easier as well.
Hang in there; everything you learn today is one more thing you didn't know yesterday... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
It was about the forth time that day someone asked somthing that was answered in the stickies.