Leakproof Flashings for Masonry Chimneys

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