I have a 2x6 header for a window in a remodel with approx 5" long cripples between the header and top plate. What is the preferred nailing schedule for the attaching the cripple studs to the top plate and header per the IRC? Its obviously a little tight and I'd prefer just to toenail 2 8D common nails if possible (one into the header and the other into the top plate)
If you can nail down through the top plate (e.g. before the second top plate is installed) then 3 12d nails is standard for 2x6 framing. For nailing the cripple into the header, toenailing should be fine, but I'd use 12d glue coated framing nails (greenish nails). Save the 8d nails for attaching sheathing.
Note, this is just personal experience, your local codes may require otherwise. It doesn't hurt to ask your building inspector what they require.
I much prefer using common 16d nails (the greenish nails) for 90% my framing. Two driven down through the lower sill plate will hold the cripples in place. Then nail the upper sill plate on top of the lower one using 16d nails. You can toenail the cripples into the sole plate with either two 8d or 12d nails on one side of the cripple and a third nail on the other side. Remember to place a cripple on each end of the sill plate and, if possible, space the middle cripple(s) on 16" center with the rest of the studs in the wall.