Expert: Bruce E. Johnson - 12/5/2008

Question
I want to strengthe roof truss (made of single 2x4 pine.
 I thought I could add anther 2x4 ( small dimensions adjecnt to make 7x1 1/2. Then clad both 2x4 s with 3/6 or 1/2" plywood (constructon adhesive everywhere. Connect plywood to dimensional lumber and lots of #8 1 1/2" screwas on both sides (and into plywood on both sides, with screws into both stacked 2x4 s.
 I did this successfully to reinforce the attic floor (30' wide trusses) I covered the floor with 3/4 plywood. solid as a rock.
 Now I wand to use the same method to reinforce the vertical diagonal 2x4 s and the 2x4 supporting the eciling.

  I want to add room extensions perpendicular to main axix of the house. The extensions will be2-stiryy conventional construction (inclusing their roofs. But I assume there will be addition stress where rge roof of the extension mate with existing roof.  From a structural perspective, have I reinforce the existing trusses sufficiently?  Is there a better/easier/cheaper wat?
   Sorry for being so long-winded.

   THANKS FOR ANY HELP/ADVICE YOU CAN OFFER??

John (Tennessee )

Answer
Hi John, I'm a little leery of giving advice regarding altering "engineered trusses".  The problem with this is that these trusses are engineered using specific formulae to maximize the lumber involved and to transfer the weights to the bearing points where the trusses sit.  I'm not too clear what you are trying to do with your addition.  Are you planning on sitting the addition on top of the existing trusses?  Merely adding more wood to the trusses may or may not help.  Whenever I have had to add weight to existing trusses the truss company did the repairs or provided a detailed sheet outlining how the repairs should proceed.  Generally the truss top chord, bottom chord and the webs were added to by sandwiching the truss between similar sized lumber..in other words the 2x4 top chord became 3 2x4's with the top chord in between.  If you have a truss company with an engineer in your area maybe you can have him look at your trusses and run the numbers to determine what you need to do to add an addition to the tops of the trusses.  You may need to add extra webs where the new addition will sit to transfer the point load back to the outside bearing walls. Or you may be able to purchase a couple of girder trusses that will support your addition without putting any load on the existing trusses. These kinds of things can be discussed with the truss engineer.   I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com