Saw-cut flashing is always installed after the brick veneer has been installed. This much-less-costly flashing method is only let-in about one-half inch deep, at the most (left). If water doesn't absorb any deeper into the brick than that, you're home free. But unfortunately, during any substantial rainstorm, it soaks much deeper and can easily go all the way through and runs down behind the ineffective flashing attempt. Proper through-wall flashing (right) runs from under the weather-resistive barrier on the structural wall and extends all the way through to the front face of the brick. Its purpose is to direct any water that finds its way into the wall cavity to the exterior.
The saw-cut flashing I typically come across is held in place with sealant and the occasional nail wedged between the metal and the brick. The sloped flashing shown here was only cut in about 1/2 inch and has simply fallen out of the wall on its own. The continuous bead of caulk used to keep the flashing in place is often installed under a misguided attempt to prevent water from “getting in.” The irony is they’ve sealed the location where water should be getting out.
A similar meager attempt was made to flash this chimney. The apron and sidewall flashings were kerf-cut in about 1/2 inch and held in place with nails and caulk—a bad idea. The chimney’s apron should be composed of a two-piece flashing with a through-wall counterflashing lapping over a separate apron flashing. The main point of installing two-piece through-wall apron and sidewall flashing is so you have the ability to remove apron, or "skirt", thereby having access to the step flashing when you reroof. This chimney is currently being taken down to roof level, and the new copper pan flashing will be installed in stair-step fashion.
This may be a firewall between adjacent housing units, but all I see is a reservoir to let water come in between those two units through the brick. Unfortunately, this is typical of what you get nowadays, and it flies in the face of building tradition.
On older buildings that have been re-roofed multiple times, the existing through-wall flashing often gets cut flush with the front face of the brick, as was the case on this parapet end wall. At some point, a roofer came in and cut off the exposed leg of the counterflashing in order to get a new roof down, and then he installed saw-cut flashing. What he should have done is left some of the exposed counterflashing in place and slid new flashing skirts under it, pop-riveting or screwing the two together.
Executing a true through-wall counterflashing along the rake of a sloped roof requires installing a series of stepped pans. In this photo, the masons began by building up the brick in stair-step fashion. The rise and run of these stair steps will vary with the pitch of the roof, but each step will be the same rise and run because the slope stays the same and the brick coursing is the same.
Next, the masons laid in copper pans. A key feature of these pans is the soldered end-dams that direct water onto the front edge of the pan. This hemmed edge extends past the front of the brick about 1/2 to 3/4 inch, providing a lip to which the counterflashing will be attached (by pop-rivets or sheet metal screws). Also note that the builder making the repairs on this job decided to install an additional layer of peel-and-stick flashing lapping into the pan. Though not required, it’s cheap insurance on this costly repair.
A double-layer WRB laps the back edge of the pan.
When everything had been cleaned up from laying the new brick, and the brick was painted, copper skirts were slid up under the front edge of each pan and pop-riveted or screwed in place. The copper skirts are further secured with vertical lock seams and serve as a counterflashing to the stepped L-flashings that the roofers wove in with the new roof shingles.
