Chimney flashing usually consists of two parts – step flashing and counterflashing. Step flashing is a “L” shaped piece of metal that is tucked up under the shingles and extends up behind the counterflashing. There should be one piece usually for each shingle that is stepped up the roof overlapping each other for waterproofing purposes. Then the counterflashing is overlaid also in a stepped appearance as shown below attached to the brick and mortar. (figs. 1 and 2)
Do It Yourself Roof Repair Brick Counterflashing Figure 1
Do It Yourself Roof Repair Brick Counterflashing Figure 2
The function of the counterflashing is to waterproof the metal stepflashing behind it.
Brick counterflashing is a longer piece of metal which steps up with the brick mortar so it can be more easily turned into the mortar joint and fastened. A groove should be cut out of the mortar joint and the metal edge bent into it so it is more secure. This enables a better seal for watertightness. Polyurethane sealant is then applied liberally with a caulking gun to make the seal as permanent as possible (figs. 3 and 4) .
Do It Yourself Roof Repair Brick Counterflashing Figure 3
Do It Yourself Roof Repair Brick Counterflashing Figure 4
Inferior sealants will crack loose sooner and be ineffective often causing chimney leaks and possibly wood damage around the chimney (fig. 5)
Do It Yourself Roof Repair Brick Counterflashing Figure 5
The chimney shown at the top of this page is simply a brick veneer as opposed to a solid masonry chimney. It is more prone to water penetration through the mortar joints which is discussed under the same Chimney Flashing menu dropdown “Masonry Sealant”.