Flashing & Moisture Control
Through-wall flashing, weep holes, drip edges, flashing materials, sills, copings, and parapet walls.
- Explain the purpose and placement of through-wall flashing
- Describe weep hole function, spacing, and installation methods
- Identify proper flashing materials and drip edge details
- Explain the design of sills, copings, and parapet walls for moisture protection
Lesson 1
Through-Wall Flashing, Materials & Drip Edges
Why Flashing Is Critical
Water is the single greatest threat to masonry structures. Even the best-laid brick wall allows some moisture to penetrate the outer wythe. Through-wall flashing intercepts this moisture inside the wall cavity and redirects it back to the exterior through weep holes. Without flashing, water accumulates inside the wall, causing efflorescence, mortar deterioration, freeze-thaw damage, and structural failure.
Where Flashing Is Required
Through-wall flashing must be installed at every point where water could accumulate or where the wall meets another building element:
- Base of the wall (above the foundation or brick ledge)
- Above all window and door heads (over lintels)
- Below window sills
- At shelf angles (where brick veneer is supported on steel)
- At roof-to-wall intersections
- At the top of parapet walls (copings)
Exam Fact
Through-wall flashing must extend from the back of the cavity, across the full wall thickness, and project past the face of the brick with a drip edge. The drip edge prevents water from running back under the flashing and into the wall.
Flashing Materials
| Material | Properties |
|---|---|
| Copper | Most durable, long-lasting, expensive; soldered at laps |
| Stainless steel | Very durable, corrosion-resistant |
| Lead-coated copper | Combines copper durability with lead's flexibility |
| Rubberized asphalt (peel-and-stick) | Self-adhering, flexible, most commonly used today |
| EPDM membrane | Rubber sheet, durable, requires adhesive at laps |
| PVC or vinyl | Economical but less durable in UV exposure |
Proper Flashing
Extends full cavity depth
Drip edge projects beyond face brick
End dams at terminations
Lapped joints sealed (min 6" overlap)
Common Mistakes
Flashing too short - does not reach face
No drip edge - water runs back into wall
No end dams - water flows off ends into wall
Unsealed lap joints - water passes through gaps
End Dams
At each end of a flashing section (for example, at the sides of a window head), the flashing must be turned up to form an end dam. The end dam prevents water from flowing off the end of the flashing and into the wall interior. Without end dams, flashing simply redirects water sideways to an unprotected area.
Through-wall flashing must extend the full depth of the cavity and project past the face brick with a drip edge. Flashing laps must be sealed with a minimum 6-inch overlap and must have end dams at all terminations.