I am in the process of replacing a dry rotted 4×12 that frames into the end of a wing wall. The house is cedar shingles over 30# felt over 1/2″plywood sheathing. I will use a treated beam for the repair. My problem is how to flash and replace shingles damaged during the repair. The beam pocket is in the center of the wing wall which extends on up above the pocket.There was no flashing originally. The house is in the forest in western Washington where it tends to rain occasionally.