I really have no idea if this is the correct way to build a soffit box but here is one possibility:
A couple things jump out at me:
1.) Note the double miter cut of the gable fascia.
2.) Note the addition of the two pieces of fascia to create the soffit box.
3.) I've shown this soffit box with a 15" return (the minimum return) however one could extend the return further and the eave soffit would then morph into an L shaped configuration. So if this type of soffit configuration is specified I should also provide the user with the ability to set the return length.
With gable roofs and their soffit and fascias it looks like I've open yet another can of worms.
A couple things jump out at me:
1.) Note the double miter cut of the gable fascia.
2.) Note the addition of the two pieces of fascia to create the soffit box.
3.) I've shown this soffit box with a 15" return (the minimum return) however one could extend the return further and the eave soffit would then morph into an L shaped configuration. So if this type of soffit configuration is specified I should also provide the user with the ability to set the return length.
With gable roofs and their soffit and fascias it looks like I've open yet another can of worms.