screw spacing in ceiling sheetrock

hey all
im hanging 4' x 8' x 5/8" firex type drywall on my garage ceiling and plan to pump in 8-10" (max) of loose insulation on top of it.
rafters are 24" apart. am i good with 12" screw spacing to hold this up? for a 4x8 sheet this basically puts 5 screws across the width, every 2'. or 25 screws for a whole board.
everything ive read seems to point to 12" spacing, and ive been told it meets code. i just want to make sure before i pump the stuff in and watch my ceiling fall due to the weight.
thx randy
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i forgot to mention. all butt joints have screws spaced at about 8" so theres a few more than 25 screws per board right now...
thx randy

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xrongor wrote:

I always double screw. In other words I put two screws about 2" apart every 12" or so.
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sure, i could overkill it.
but is 12" centers 'enough'?
randy
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xrongor wrote:

It's not overkill to scores of professionals.
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I did that in my 20's, but in my late 50's I don't any more.
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Edwin Pawlowski wrote:

Maybe some mood lighting and proper music? Oh, and viagra.
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xrongor wrote:

USG calls for 12" OC screws as maximum spacing. Don't be pennywise. Go with 8" OC. It'll cost you an extra fifteen minutes of your time and a few bucks for the screws.
USG also "strongly" recommends double-nailing ceilings to prevent pops, but does not require double-screwing.
The 5/8" board is maxed out with joist at 24" OC if run perpendicular - if you run it parallel, it's only good for 16" joist spacing. You could go with the 1/2" sag-resistant ceiling board - good for 24" joist spacing either way, and you'd save some of the weight. I'd contact USG and ask their recommendation on which board to use with that much insulation.
R
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but why is there such a discrepancy? my local inspector told me that 12" centers is good enough for up to 12" of blown in insulation on top of the 5/8 firex. code normally has some fudge factor built into it... if code says x is enough, why does everyone seem to suggest using x+1?
have you seen an actual failure when someone used 12" spacing?
i mean you don run 10 gauge wire when 12 will do, just to stop from being pennywise... you dont make fishing poles out or rebar either...
randy
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xrongor wrote:

In the time you've spent pissn' and moin' you could have had it done. Go 8" if you're concerned and quit fretting over it for krist's sake.
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G Henslee wrote:

PS. -end of subject-
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ah man. now i remember why i unsubscribed before.....
come on richard. why 8 inches? you got any info about the structural strength of sheetrock that i cant find on the back of a cereal box?
anybody? buhler? buhler?
randy
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Spanning 24" with 5/8 sheetrock seems a little far.
I'd me more concerned about the 24" than the 12" screw spacing
btw

not necessarily, code making involves a fair amount of compromise & is very dependent on the personalites invloved, some times it's just worng, some times un-conservative, some times overly conservative

because "the code is a minimum standard"........kinda like a doctor who just barely passed med school.
For example, the allowable joist spans (esp for long spans) will yield a floor that, for many people, is jsut too bouncy, but it's code. A
Put the extra screws in, you'll be glad you did. hink about about it, if a screw fails the closest screws in one direction is 24" away, in the other 12".
cheers Bob
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