Since you have two main things going on with the bumpout - the whole thing is wider and you are loosing the hip end - You'll find it easier (and certainly stronger) to remove the entire roof from the old bumpout section and replace it with engineered trusses. This will keep the roof framing out of 2x4 yet will be strong enough to span the new width of the addition. You 'll still have a small transition overlay area on the inner side to make the new roof structure above the old, but this can be stick built. Since the major portion of the new roof will be engineered trusses, the code guys will allow a fair amount of leeway if you have to get 'creative' on the overlay section.
Removing the entire roof from the bump out was the plan. That creates the issue with the birdmouthing of the 2x6 rafters on a 2x4 top plate, while matching the existing roof.
I can't use trusses - the cieling joists run perpendicular to the rafters, so the truss wouldn't clear them, I wouldn't think... would they? -NickThis message has been edited. Last edited by: Nick C,
You will remove the existing ceiling joists and use the bottom cord of the trusses as the new ceiling joists.
Another thing to consider is that you may be best off with a slight roof elevation change. Your pitch is going to be tricky to match and look right since you are moving the peak of the new addition over towards the right - Cutting off the entire roof over the new area and raising it slightly in relation to the old roof means that you do not need to be concerned with moving the ridge over the un-remodeled section.