I am adding a 14x14 porch addition to my existing house. I have built and raised both side walls along with the gable balloon wall to a 4 in 12 pitch. My rafters are 2x 10's with the ridge beam measuring 11 3/4 inches in height. Even with the plumb cut on the rafters they won't reach the full hight of the beam. If I set the rafters at the bottom of the beam then I would have to trim the top of the ridge beam to meat the sheathing...not a good idea. Plus, no ventilation. If I set the rafter to the top of the beam I still have that ventilation issue...plus my beam is hanging a couple of inches into the room below. The only thing I can think of is to raise the rafters 1 inch above the beam top to provide proper ventilation and deal with the dropped beam later from the inside. By the way the ridge beam is two 1 3/4 inch x 11 3/4 lvl's sandwiched together. I have 3 roofing books and I can't find anything on this configuration.....Any thoughts would be appreciated. Thanks in advance. Dave
Usually, the ridge beam does extend below the bottom of the rafters. If you're worried about finishing the underside of the rafters, you can put a board horizontal across the bottom of the ridge at the peak, this will give you a place to mount lights, ceiling fans, etc.
As for insulation, if you're using 2X10's, use faced insulation for a 2X6 wall. The facing paper goes down, stapled to the bottom of the rafters so the un-faced insulation is still about 3" below the roof decking. This leaves room for the roof to vent above the insulation.