Expert: Bruce E. Johnson - 10/13/2008

Question
QUESTION: I am having a house built and the builder ordered Top chord bearing floor trusses.  I am concerned about top chord bearing floor trusses.   Can the metal plates actually support the weight of kitchen appliances, cabinetry, etc that will be loaded on the floor
directly above these.   Just looking for some assurance that the floor will not collapse from weight above.  Doesn't seem to be much holding on to the top 2x4.

ANSWER: Hi Joe, if the trusses are built according to appropriate specifications made by the structural engineer, i.e.  30-40 pounds live load and 15-20 pounds dead load, or whatever was spec'd by the architect/engineer, then you should be fine.  I use top chord bearing trusses all the time without problems.  Remember that there is only an inch or less of the top chord that makes up the shear value of the truss.  The shear value of the top chord at that point from where the truss bears on the wall and the point where the top chord ties into the bottom construction of the truss.  That distance is at most an inch or so.  The shear of that wood in that inch is incredible, probably close to a thousand pounds.  Multiply that times each end of every truss and you will see that your floor system will support a heck of a lot of weight.   I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

---------- FOLLOW-UP ----------

QUESTION: Are there problems with the plates coming loose and causing failure with the top chord bearing trusses?

Answer
Hi again Joe, generally speaking a truss is a truss and they are all made with those gang nail or pressed plates.  So the answer to your question is "no".  Can they ever fail?  It's possible that some have failed over the last 60 years that they have been in use.  But I am sure that the failure rate is infinitesimal compared to the non-failure rate.  How the trusses are handled also has a lot to do with the failure rate.  As long as the joists were handled in such a way that the plates did not undergo undo stress causing them to loosen then again you should be okay.

 I'm not sure why you are making a big deal over this unless you don't have any confidence in your engineer or architect. If this is the case then perhaps you need to consult another engineer to verify that the present structure is capable of bearing the weight you are concerned about.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com