maximum ceiling deflection

huangyhg

maximum ceiling deflection
i have a wood frame house that has ceilings that sag. the house has plaster. what is the maximum deflection allowed before cracking will occur such as inch/foot? also any suggestions on how to repair a sagging plaster ceiling?
thanks
john
check out our whitepaper library.
rbg:
its tough to design via the web, and i hesitate to do so.  without knowing the actual dead load of your ceiling/attic etc. i'd have a hard time engineering it for you.  i would suggest that you keep trying the local engineers in your area.  especially the smaller firms (one-man firms) etc.
as a rule of thumb, the required beam depth in inches is approximately .45 times the span in feet.  so for your 26' span beam you'd need about a 12" depth.  now the weight size would depend upon the actual design loads.  is the attic accessible?  if so, a heavier beam might be needed for possible storage loads as opposed to a 10 psf attic live load.
the lvl's you sized look plenty strong for the new 13' span.