I am not a carpenter, so please forgive me if I use some terminology wrong. I will do my best to describe my situation, and then my question.
I have an existing "lean-to" style porch roof that itself seems in good shape, but the structures that support it don't make much sense to me, so I am starting a project to upgrade\repair\reinforce the supports for the roof. On one side, the rafters are toe-nailed to a ledger board at the house. On the other, they are set atop a single 2x6 beam (the roof beam length is about 15'). The beam is supported by 4 columns\posts (this is where we get to the odd part). The posts consist of 4x4s that run from the footings (currently a cinder block buried in the ground) up to along side the beam and connected to the beam with lag bolts and nails. There is a 2x4 attached to the side of the post with lag bolts that sits below the beam but does not extend all the way down to the footings. All 4 columns are of this type of construction. I tried to make a simple sketch of what I am describing:
My plan to upgrade this entails digging new, proper footings ( I am in the north east US), replacing the columns with 6x6 posts, and adding an additional 2x6 to double up (laminate?) the existing beam. Like this:
So my question is about attaching the new 2x6 beam to the existing one. All the information I can find online says that the proper way to do this requires a fair amount of nails driven through the boards in both directions. My concern is that all that hammering against the beam in the direction away from the house may cause stress or start to pull the rafters away from the ledger (the roof is currently finished with asphalt shingles on top). Is there any type of screw that might be acceptable to use in this scenario? It seems like driving screws in might be a lot less stress on the structure. Or would a nail gun be better or worse in this case than a hammer?