Hi TCB,
First...
...Big Welcome to the TFG forum...!!! Glad you have joined...
I see you have two posts so, I will make this one my first to respond to...
I was thinking a ~4ft overhang...Can an overhang this large be supported by just the rafter(s) of the roof frame(s) extending outward, or is a gusset brace (or even a vertical post) a guaranteed necessity for this size of cantilever?
Depends on the design of the architecture, the timber size/species, and load exposures for the area...Snow isn't your challenge at all, as I was just in Katy, Texas not long ago...however, wind is a challenge.
A 1.2 m (~4 feet) is not hard to achieve at all. Even 3 m (~10') overhangs are achievable without any obstructing members to block free passage, yet this size (the largest I have personally examined) is not a typical or easy design to facilitate within the context of most domestic architecture...
What type of rafter-extension is usually done for the really wide overhangs sometimes seen?
If you mean by "type" the most common designs, I am afraid they would be voluminous to list here...Green and Green Craftsman/Prairie style is the first that comes to mind for a "homegrown" design motif, but there are many vernacular folk styles from the Middle East, Asia and beyond that also have very large overhangs.
For very local (and indigenous) design flavor the Creole/Choctaw styles that developed both pre and post Spanish/European migration to the areas of Texas have roots in local design motif...You can find
Bousillage and Spanish styles both in Texas and these can have very large overhangs and veranda...
In the European modalites, large overhangs are not typical, yet the Swiss have excelled at this probably better than any other cultures of Europe. There are forms of timber architecture found in Eastern European that can have large over hangs and also the Moorish influenced styles found on the Iberian peninsula...
If "type" meant timber size...that would all depend on design...
I figured the usual birdsmouth jointing at the frame cap would eat up too much of your cross section to stick out very far, but those are the only type of rafter/wall joint I seem to be able to find detailed explanations of (well, roof sprockets count, but I was hoping for something that continues the same shallow roof incline as the main rafters)
This is a complex and deep "rabbit hole" we are entering...It is so nebulous to approach without a "focal point" design as to be inhibitive without some form of goal or context in understanding what might be the possible target..If perhaps you have some more specific ideas or goals, perhaps then we could explore more specifics design parameters and then just begin to explore what might be possible...
