plaster/rock lath ceiling construction

[PSUengineer1]

ceiling construction is as follows:
1.Floor joists
2. 3/8 drywall attached with nails at random spacings. Some of the nailings are with 2 nails at connection, spaced more than 12" o.c.
3. rock lath and finish coat of plaster below drywall.
4. the thickness of the ceiling (total) is up to 2-inches thick in the area of collapse. 16x16-inch section weighs about 20 lbs (about 11.5 psf).
5. no adhesive used in attachment of ceiling.

Ref: IRC Table R702.3.5 for additional info.

I opine that the weight of ceiling too heavy, any code references out there regarding allowable thickness of this type of ceiling construction? Otherwise, check out attached pic of nails used for attachment. I do have evidence of "double nailing" used at more than 12" o.c. but not sure if there were intermittent nails used.

Looking for comments.

Thank you.

 

[BAretired]

If nobody was injured or killed, the owner should consider himself lucky. Whoever installed that ceiling should consider another vocation.

BA

 

[AELLC]

I am not aware of any ceiling allowable thickness in the IBC. It is just a matter of calculating nail withdrawal capacity vs load at each nail.

 

[Ron]

Generally, the fasteners should be spaced at 7 inches on center for the lath attachment. Since this is rock lath, the spacing would likely be a bit more than for expanded metal lath. Check with the Gypsum Association for the appropriate fastener spacing for horizontal attachment. The failure appears to be a "pull over" failure, indicating the dead load was too high or that moisture caused a weakening of the gypsum in the rock lath.

One other consideration is that the rock lath and the old gypsum board, as well as the plaster, likely contain asbestos. Get it checked before you demolish.

Refer to ASTM C1063 and ASTM C926 for portland cement plaster. For gypsum plaster, see ASTM C843. The gypsum plaster should be about 5/8" thickness.

 

[hokie66]

The 3/8" drywall didn't have enough support itself. Then along came some idiot who thought a plaster ceiling could be supported as well off those same nails. I doubt there is a "code reference" for this type assembly, in regard to hanging one type ceiling off another.

 

[Ron]

Come on hokie...don't sugar-coat it. Tell us how your really feel!