I'm not sure if we had codes here in 1923 when the house was built.
I'll try to explain the roof's construction as best I can-My apologies for lacking the vocabulary and roofing insight.
-The roof is a simple gable form. Not even a dormer to work around.
-The wiring is the old knob and tube type. And it is often covered with insulation. So I am not able to see much or poke at the house's skeleton.
-Each half of the roof is 30' x 17'8" (30 feet at the ridge). Both halves are the same (except for the back porch that continues another 3' x 12' ).
-The eaves have about a 30 inch overhang all the way around the house.
-The ceiling joists seem to be 2x4. I can't see if they are joined anywhere or not.
-The house's foot print is 30'x24' (24' corresponds to the 30' ridge in the center of the house).
-The wall support is two 2x6 boards. The rafter is secured to the wall edge by a large dado(?) type cut in the 2x4.
-Fortunately there doesn't seem to be any sagging except along the rake edge where the eaves were repaired by a previous owner.
-The half span would be 15 feet.
-The ridge beam is supported at the gable ends of the house and the rafters. The rafters are supported in part by the 1x6 boards cut at a slight angle connecting the ceiling joists to the rafters. The 1x6 sheathing should also provide support for the rafters.
Can adding new rafters in between the old ones be done economically and without disturbing the existing guts i.e. electrical and existing roof? Can you think of an alternative?
And to think, I wanted a little bungalow.
Thank you again for your help.
