Roof to Sidewall Flashing
Tim Healey This illustration was adapted from Chapter 4 of The NRCA Roofing Manual: Steep-slope Roof Systems—2013. The bubble at lower right shows the detail in NRCA ASPH-12A, which uses a one-piece counterflashing. The bubble at upper right and the main drawing show the detail in NRCA ASPH-12, which uses a two-piece counterflashing.

Step flashing should only be fastened to the roof deck. Do not fasten step flashing to the wall on the vertical leg. Doing so would prevent you from removing it without removing the siding. While a single-piece counterflashing (shown in bubble lower right) will work, the more elaborate two-piece counterflashing shown allows for inspection and replacement of the underlayment, including any adhesive flashing membrane, which is also recommended to protect the wall to roof intersection. Even with a two-piece underlayment, there is no need to fasten the step flashing to the wall.

For more on flashing roofs, visit the JLC Field Guide.