Expert: Dan Griffin - 8/14/2009

Question
I am using 4/8 cedar beams to span 20' to cover an existing deck. The problem is that the customer would like to have 4/4 posts for the vertical support that holds up the outside beam that the spanned beams will seat on to maximize the view. Coming off the ledger besides the metal roof on top I am worried about the sheer and the structure racking. Do you have any suggestions to sturdy it up ? It is 20 by 36 and I have 45s on the corner beams for some lateral bracing. thank you

Answer
William, you need to worry about sheer, rack, and uplift as well as snow and wind loads pushing down.  Here are a few ideas:

Heavy metal strapping (16 gauge galvanized comes to mind) used as x bracing in the flat under the roof decking.  This x bracing would need to securely tie the ledger to the outside rim joist, and be well fastened at each purling intersection.

Simpson makes moment frames that are designed to deal with sheer in very small wall sections.

Knee braces can serve much of the function.  These can be fabricated in steel to maximize view.