Best way to finish trim transition for pitch transitioning roof

Good day, everyone,

I have finally reached the point where I completed framing of the new sunroom/covered porch combination and am working on finer details. The new roof is a lower sloping (3/12) barn roof that attaches to main roof (about 6/12). To tie the new roof to old, I nailed on a piece of 2x12 directly to old rafters in the middle of the roof, cut new roof rafters at an angle to attach flush to this board. I then ran and overlapped OSB sheathing and connected two roof sheathings. Left side of this structure does not go all the way to the end of the existing house, therefore, it will terminate normally, with built up siding wall between old roof and new roof (similar to a dormer). The right side (pictured below) terminates in line with current roof’s rake, therefore, extra overhang of old roof below the connection will be trimmed and the existing siding wall will be continued for the new structure. However, I cannot seem to decide best way to form the fascia board and subfascia at the new rake.

I have created 3 options. The most important thing I consider is the structure - I want not only the new rafters to securely attach to the 2x12 board from the top, but also securely tie in the old rafter below to the board to prevent sagging in the future, since 2x12 is the only thing that holds overhang of old roof on bottom of it. If I only depend on the sheathing and ladder to hold old overhand, it may sag over time without attachment to a very sturdy 2x12.

Now, Options 1 and 2 are (in my opinion) the sturdiest, as they provide more full-size 2x6 bottom rafter for support attachment, but yet create the largest box.

Option 1:

Option 2:

Option 3 is the neatest looking, as it basically eliminated the “box” idea and keeps the fascia size the same everywhere, but requires more cutting of old rafter (and some 2x12 also), while reducing the strength of connection.

Any opinions from roofers and builders for what is typically done (or any other recommendations) for both structure and looks.

Thank you.


That is known as a shed roof, gambrel roof is barn style. #3 would look best. Extend your top plate out on the bearing walls to support your fly rafter. What are the dimensions of existing soffit and fascia?

Well, I came to find out that “normally” the fly rafter is a size smaller than common rafters. In my build, I used same size 2x6 for common rafter as I used to fly rafter also. The original house’s fly rafter is 2x4, commons are 2x6. The fly rafter is supported by the porch beam, very stable support - both bottom and top. The existing roof rafter is supported on one side by the chimney and the other side runs below the new rafter. Both will attach to 2x12 plate that I ran on existing rafters for new shed roof support.

What are soffit and fascia dimensions?