A properly flashed chimney is protected by the overlap
between the base flashing and the counterflashing. This twopart
system absorbs any building movement that may occur
(when new house framing shrinks, for example). Base flashing
is installed as the shingles are applied, and generally consists
of the lower base pan, step flashing, and the upper pan or
cricket. Most builders are comfortable installing the base
flashing, because the roof sheathing provides a solid nailing
base. But what about the counterflashing?
In the Groove
Many contractors make the mistake of fastening the counterflashing
to the side of the chimney, using masonry screws
to secure the flashing to the side of the chimney, then