Brick structures , he says , are generally not waterproof to begin with. Water can get into brick wall with ease. Modern day homes tend to only have brick facades , meaning the wall is just one layer thick , compared to older homes that often have a few more layers. The thicker walls were designed to be more water resistant.
While the brick itself is very resistant to water passing through it , and to a degree the mortar between the brick , the interface where the mortar touches up against the brick provides a pathway for water to enter into a brick wall. You can’t see this crack because it’s often very small , but it exists.
The best practices published by the Brick Industry Association call for flashings under window and door sills. These flashings collect the water that leaks through the mortar joints and redirects it to the outside of the wall.
Base flashings are also required under the first course of brick as well as at other locations on brick veneer walls. Other materials are often placed behind the brick veneer to ensure that wet mortar falling behind the brick doesn’t block the flashings and any weep holes at the base of the brick walls. These weep holes are installed on purpose and allow the water to flow out of the wall. It requires a significant amount of skill and attention to detail to do all the things needed to ensure a brick veneer wall does not leak.