maximum ceiling deflection
 

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
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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.