What Thickness for Ceiling with 1' joists

HooKooDooKu

What thickness of drywall would you suggest for the ceiling in this basement/den application:

The floor joists above are 2x8s on a 14.5 foot span on 12" centers. The floor had been boucy for years so I sistered up every 3rd joist with a 2x10, and attatched 2x4s laid flat under the rest of the joists (plus blocking).

I've heard the general wisdom is to use 5/8" drywall on ceilings to avoid sagging, but I figure on 12" centers, 1/2" wouldn't have a sagging issue (would it), not to mention easier for one person to install. Of course on the flip side, the history of bouncy floors makes me think I might want thicker for strength.

Input?

DangerMouse

HERE, code requires 5/8" Fire-X drywall to be on the ceiling.
Not sure how this applies to you though.

DM

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HooKooDooKu

Why Fire-X 5/8" on a ceiling?

I know current codes require drywall (and likely Fire-X 5/8") for the ceiling of a garage to help prevent an engine fire from spreading to the rest of the house... and I know my walls between the garage area and the new living space requires Fire-X 5/8"... but why the ceiling? Are all ceilings required to be Fire-X 5/8"?

DangerMouse

Idunno, but my inspector told me that's what I had to use inside the house, in all new rooms. Maybe it's a newer IRC update?
Hard to say, I just do as I'm told! LOL

DM

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gregzoll

Code has always been 5/8 for ceiling. Does not sag, and stands up to not allow a fire to get into the above living space too quickly, so that people can get out. As for your floors being bouncy, did you ever have a engineer come in to investigate why? 2x8 are sufficient enough for floor joists, especially if 12" O/C, should be 16" O/C.

Scuba_Dave

I've never heard that 5/8" is code unless the rafters are 24" apart
1/2" is used normally here

2x8's 12" OC will span right around 15' +/- depending upon wood species & grade
That's for a bedroom 30psf

gregzoll

Here it is 5/8 for ceilings, and 1/2 for walls.

Gary in WA

“Water-Based Spray Textures on Gypsum Board Ceilings

SUMMARY
The phenomenon of sagging 3/8 inch gypsum board on ceilings framed 16 inches on center and 1/2 inch gypsum board on ceilings framed 24 inches on center after application of water-based ceiling textures is well documented by field reports and laboratory experiments. A viable, low cost solution to the condition is to increase the minimum thickness of the gypsum board to 1/2 inch gypsum board for framing spaced 16 inches on center and 5/8 inch for framing spaced 24 inches on center. This recommendation has been reflected in gypsum industry literature for many years. The Gypsum Association is not aware of any scientific evidence that would warrant a revision to this recommendation.”
From: http://www.gypsum.org/topical.html#waterbased

If your floors are bouncy- individually, you could add blocking or better yet, bridging so they act act a unit dispersing a given load: http://books.google.com/books?id=DWs...olumns&f=false


Be safe, Gary

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boman47k

Alabama here too. I always thought it was 1/2" for ceilings with 16" oc. 5/8" on 24" oc. From reading the forums it seems people all over the country use 5/8 for ceiling. Maybe they have different spaced joists.

I can understand fire rated for a basement.

bjbatlanta

1/2" is fine for 16" (or less) centers. Use 5/8" if it's code where you live.

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HooKooDooKu

When I tried checking into floor joist span tables, I was finding something more in line with only 14' span on 12" O/C, but I think I was going off of a 40psf load for a living room. In my case, the actual span was 14'6". The bounce wasn't so bad that you could feel it walking around, but from the 1st day we moved in, you could hear furnature (specifically the entertainment center) rattling as you walked through the room.

In any case, the bouncy floors have been improved. One of the other reasons for the bounce was that when the builders used metal straps to connect the floor joists together, they were using straps sized for standard 16" O/C joists, and they just slapped them up there, some simply nailed on the back side of the board, almost none of them under ANY tension (you would wiggle them with no problem).

So like I said, I pretty much took care of the floor bounce by sistering some of the joists with 2x10s, added two sets of blocking (each set about 5' from the wall), I pulled the nails out of the straps, pulled them into a little bit of tension with a come-along, and shot a new nail through the strap (so the joists are now tied together in three places). Then as the final step, nailed/screwed/glued a cut-to-length 2x4 to the underside of each 2x8 to form something of an upside-down 'T' beam.

I've been happy with the results... except for the issues it has caused mounting other things in the ceiling that expects floor joist to be 16" O/C and NOT have 2x4s laid flat on the bottom of the joists. I've had to effectively jerry-rig ways to mount ceiling fan boxes and a few recessed lights.


BTW, I found where Table R702.3.5 of at least the 2006 IRC specifies thickness of gypsum board needed for various applications. The smallest for ceilings is 3/8" with 16 O/C oriented perpendicular to the framing IF a textured finish is NOT going to be applied to the ceiling. 1/2" can be used with 24" O/C, but similar to the 3/8", if it's that thin, you must orient it perpendicular to the framing, and you must go with a thicker size of you are going to apply a textured ceiling.

bjbatlanta

If you check around, 3/8" is generally more expensive than 1/2" to begin with. Aside from that, I would never go with the bare minimum "allowable". The next owner may decide he/she wants texture. And I'm guessing you're just tossing out that information and not considering actually using it....

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HooKooDooKu

I'm planning on 1/2" minimum. I'm not worried so much about the "next" guy as we plan on being in the house for a while... as such, I'm really interested in what is going to hold-up and last. But this is a one-man show, and from have handled some 1/2" on a wall, I was 2nd guessing the original plan to use 5/8" on the ceiling if it was reasonable to use 1/2".

bjbatlanta

1/2" will work fine in your case, and as you said it's much easier to handle. Best of luck....

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