Expert: Bruce E. Johnson - 1/26/2010

Question
QUESTION: Hi, I had a 20x26 bedroom addition built on back of my ranch house.  I used 50' clear span roof trusses 24" OC with 5/12 pitch.  The other half of the trusses was used to cover an existing sunroom that had a flatroof.  My contractor did not frame the exterior was correctly and my building inspector failed the framing.  I had to frame the interior of the bedroom wall in 1/2 plywood to minimize the wall defection.  I am unable to frame the interior of the sunroom wall with plywood because the entire wall is mostly glass.  The inspector said that I must run two header beams (doing the job of a srongback) of 3 2x10x15' or 2 2x12x15' from the outside wall and tie then into the rafters/load wall of the house.
I do not like the idea of having to cover these ugly beams that will be exposed in the middle of the room (the ceilings are vaulted).  Can I use three 4x6x15' white oak beams to strengthen the deflection of the outside sunroom wall?  In other words can three 4x6x15' oak beams replace two double 2x12x15's?  These will not be load bearing per say but used to lock the outside wall into the roof of the house.  Thanks for your help.  Andy

ANSWER: Hi Andrew, I think the inspector is creating an overbuilt situation. If anything you should be able to accomplish your bracing up inside the trusses with extra rat runs, diagonal bracing, and web bracing.  Without actually seeing your situation it's hard to give a definitive answer.  I suggest that you contact the truss manufacturer and put the onus back on them.  They should be able to give you the design fix you need without adding a bunch of unnecessary beams etc.  This is their job.  Engineered trusses are designed for specific applications and it is up to the manufacturer to provide the truss bracing etc. to accomplish your needs.  I find it very unusual that an inspector would override truss drawings and bracing requirements.  He is overstepping his bounds.  If you have signed and sealed engineered drawings his job is to make sure that you do what the drawings call for, not to redesign the roof system because he doesn't like it.  I hope this information helps, please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

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

QUESTION: Thanks for the answer but I am afraid I did not pose my problem correctly.  The issue does not lie in the trusses.  The outside last truss clear spans both room.  We used gable studs toe nailed into the top plates of the outside wall.  There is a "hinge" effect where the wall frames from the top of wall plate to the bottom of the truss.  The inspector said that the wall framing must go from the bottom plate all the way up to the bottom of the truss.  Since the exterior walls were already framed this was not possible.  I can grab the exterior wall and shake it because it is only secured with toenails into the gable studs.  Covering the inside wall with plywood has strengthend up the one wall but the glass wall has to be strenghtned another way.  Thats why he wants me to anchor the wall to the house with the 2x framing.  I wanted to use the oak beams more for an astetic reason and wanted to know if the oak would tend to sag over that 15' span.  I could go with a thicker beam maybe a 6x10 douglas fur timber.  I was quite happy that the inspector pointed this defect out to me and is not forcing me to restud the entire exterior wall.  So my real question would be;  Would a 4" x 6" x 15' white oak beam properly anchored at both ends sag over time?  There will be no weight on the beam besides the weight of the beam itself.  Thanks again, Andy  

Answer
Hi again Andy, I understood your question the first time.  I guess you didn't understand my answer.  What I am saying is that you can create your bracing up in the trusses and then just make sure the wall is tied into the trusses properly.  By stiffening the plane of the bottom chord of your trusses you eliminate the wall movement also.  I'm telling you that you need to contact your truss company and have them solve this problem for you based on the trusses used.
The beams the inspector is calling for don't have to be below the ceiling plane.  If you get the ceiling plane braced properly then you can put any kind of beam below the ceiling for decorative purposes. I hope this information helps, please feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com