Step 1: Layout
Think through the placement of the cut in light of maximum strength for the joint and overall structure. The knee brace area is a natural location for support at the new joint. Lay out the plumb cut line with a torpedo level here.
Step 2: The cut
Because of limited space, I’ve found it’s best to drill a hole before cutting to give the jigsaw blade access. On cuts like these, it’s worth noting that the cut is not likely to be perfect, as jigsaw and Sawzall blades have a tendency to waver in this old-growth fir. For a better fit, scribe the joint on the new piece to the cut on the old piece.
Step 3: Remove the damaged piece
The gable end fascia is also attached by nails that are used in every piece of the original beadboard soffit, so I find it best to use a Sawzall with a bi-metal blade to cut these nails off. Now cut the shank off the nails—this will make it easier to separate the piece without undue stress on the surrounding components. Be careful as you make your extraction; preserve the old piece for a pattern to match the new one.
Step 4: Scribe the piece
It’s pretty simple to scribe and cut a piece of wood when you have a pattern to follow. Keep in mind that the jigsaw blade doesn’t always track properly, so the cut on the original might not be square. I like to cut the new piece a little long so that I can carve out what I might need to make for a tighter fit.
Step 5: Make the cut
Use a circular saw with a high-quality 60-tooth blade to make the cut nice and smooth (and with minimum tear-out). Then I fit the piece to see what material, if any, I’ll need to cut away for a tighter fit before making modifications as needed. This is a butt joint, but the camera angle makes it look like a scarf joint when installed. Though a scarf joint is used in many applications, it’s not an advantage here.
Step 6: Mark for the Kreg jig
I like using my Kreg jig for cutting pocket screw holes; a handy tool for rough work like this. The Kreg jig is designed to sit perpendicular to the edge cut, but in this instance, there is limited working space at the soffit cavity. I want the screws going parallel with the slope of the roof so that I can get my screw gun and bit in there to set the screws. To accomplish that, I position the Kreg jig so it’s parallel with the grain of the wood. Make sure the guide hole used in the jig has the proper setback at the point where the drill bit intersects the plumb cut, accounting for the size of the screw you're using.
Step 7: Glue the joint
I like to use glue to help secure the piece at the joint. I’ve chosen Gorilla Glue which expands as it cures. Glue will help fill any voids to maximize the bonding surface. Remember when using Gorilla Glue—both bonding surfaces need to be moistened for the glue to maximize its strength. An added bead of construction adhesive can be placed along the interface of the soffit and fascia, which will hold the beadboard secure when nailing proves to be impossible.
Step 8: Secure in place
I like to use pocket screws for a stronger joint. I also prefer pocket screws to hold the piece while the glue dries. This will ensure things stay in place during the curing of the Gorilla Glue. As an added layer of protection, clamp the front surface of the fascia while the glue dries. It’s always best to hide the screws on the protected side of a piece, so there is no opportunity for moisture to get behind the plugs or filler. Quality is in the details.
Step 9: Final cleanup
Once the glue dries, remove the clamp and sand the surface. I like to use SculpWood Two-Part Epoxy as our filler. After you spackle and sand, I like to pre-prime with a good oil-based primer made for all exterior surfaces. The last thing I do is make a piece of flashing with a perimeter drip edge that fits between the roofing and the top of the fascia tail for long-term protection. Secure the flashing with a quality adhesive caulk.
Following these few steps with care should lead to a professional, attractive, and long-lasting solution.