Flashing a brick wall involves installing a waterproof barrier to direct water away from the structure, primarily crucial for effective moisture management within brick veneer systems and other masonry constructions.
What is Flashing and Why is it Important for Brick Walls?
Flashing is a thin, continuous material, typically made of metal or flexible sheets, installed at junctions, penetrations, and critical stress points in a building envelope. Its primary purpose is to prevent water ingress and direct any water that penetrates the outer layer of a wall system safely to the exterior.
For brick walls, especially brick veneer systems which feature a cavity between the brick facade and the structural wall, flashing is indispensable. Moisture can inevitably enter the cavity through mortar joints or hairline cracks in the brick. Without proper flashing, this trapped moisture can lead to:
- Structural Damage: Rotting of wood framing, deterioration of sheathing, and corrosion of metal components.
- Mold and Mildew Growth: Posing health risks and degrading indoor air quality.
- Efflorescence: Unsightly white salt deposits on the brick surface, indicating water movement through the masonry.
- Freeze-Thaw Damage: Water freezing within the brick or mortar, causing spalling and cracking.
- Reduced Building Lifespan: Compromising the integrity and appearance of the structure over time.
Effective flashing acts as an internal gutter system, collecting this water and channeling it back out, preserving the building's integrity and durability.
Types of Flashing Materials
The choice of flashing material depends on various factors, including durability requirements, cost, compatibility with other materials, and installation complexity.
| Material Type | Characteristics | Common Uses |
|---|---|---|
| Metal Flashing | Highly durable, rigid, long-lasting, fire-resistant. | Base of walls, lintels (above windows/doors), sills, parapet walls, through-wall applications. |
| Copper | Excellent corrosion resistance, malleable, premium. | High-end, long-term installations. |
| Stainless Steel | Very strong, corrosion-resistant, less malleable. | High-stress areas, commercial applications. |
| Galvanized Steel | Economical, zinc coating for corrosion protection. | General purpose, may corrode over time if coating is compromised. |
| Aluminum | Lightweight, malleable, good corrosion resistance. | Lighter applications, often painted or coated. |
| Flexible Flashing | Pliable, often self-adhering, easy to detail. | Window/door openings, curved surfaces, transitions, as a counter-flashing. |
| Asphalt-Modified Polyolefins | Self-adhering, good temperature range. | Common for general wall openings. |
| Butyl Rubber | Excellent adhesion, high flexibility, UV resistant. | Demanding applications, often preferred for superior performance. |
| PVC (Polyvinyl Chloride) | Economical, flexible, but may have limited temperature range or UV stability. | Various non-exposed or less critical applications. |
How to Flash a Brick Veneer Wall: A Step-by-Step Guide
Flashing a brick veneer wall is critical for managing moisture within the wall cavity. The process ensures that water penetrating the exterior brick is collected and directed out.
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Prepare the Support Ledge and Weather-Resistant Barrier (WRB)
Ensure the foundation, concrete slab, or steel shelf angle that supports the brick veneer is clean and prepared. The weather-resistant barrier (WRB), such as building paper or house wrap, should already be installed over the structural sheathing. This barrier prevents moisture from reaching the interior wall components.
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Install the Through-the-Wall Flashing
As per standard practice for brick veneer, install metal or flexible through-the-wall flashing. This flashing is specifically designed to extend from the interior of the wall cavity to the exterior face of the brick.
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Positioning Behind the WRB: The flashing starts behind the bottom edge of the weather-resistant barrier. This "shingle lap" principle is crucial: any water running down the WRB will flow directly onto the flashing, ensuring it's captured and not allowed to bypass the flashing system.
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Extending Down and Out: The flashing then extends down and out across the support ledge. This creates a continuous path for water. The flashing should extend beyond the face of the brick, typically by about 1/4 to 1/2 inch, forming a drip edge. This overhang prevents water from clinging to the brick and re-entering the wall.
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Hangs Down: The portion of the flashing that extends past the brick face hangs down, directing water clear of the wall below.
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Integrate with Masonry
The flashing is typically laid on a mortar bed or integrated into a mortar joint within the bottom course of brick or directly above a shelf angle. It should be securely adhered or mechanically fastened to prevent movement and ensure a watertight seal.
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Incorporate Weep Holes
It is essential that weep holes are included in the bottom course of brick directly above the flashing. Weep holes are small openings (usually vertical head joints left open or fitted with wicking material) that allow any water collected on the flashing to drip out and down the flashing to the exterior. Without weep holes, water would accumulate in the cavity, defeating the purpose of the flashing. Weep holes are typically spaced every 24 to 32 inches on center.
Key Considerations for Effective Flashing Installation
- Shingle Lap Principle: Always ensure that upper layers of building materials (like WRB) overlap lower layers (like flashing) to direct water downwards and outwards.
- Continuity: Flashing must be continuous and uninterrupted, especially at corners and changes in elevation. Any breaks can create pathways for water.
- End Dams: At the ends of horizontal flashing runs (e.g., above lintels or on shelf angles), create "end dams" by turning the flashing up a few inches. This prevents water from running off the sides of the flashing and back into the wall.
- Proper Slope: Flashing should have a slight outward slope (typically 6-10 degrees) to facilitate efficient water drainage.
- Material Compatibility: Ensure that the flashing material is compatible with adjacent materials (e.g., mortar, sealants, other metals) to prevent corrosion or degradation.
- UV Exposure: For any exposed flashing, choose materials that are UV resistant to prevent breakdown from sunlight.
- Workmanship: Proper installation is paramount. Even the best materials will fail if not installed correctly, with attention to detail and adherence to manufacturer guidelines and building codes.
Common Flashing Locations on Brick Walls
While the base of a brick veneer wall is a primary location, flashing is required at various other points to protect the structure:
- Base of the Wall (Foundation): Prevents rising damp from the ground and drains the wall cavity.
- Above Openings (Lintels and Arches): Installed over window and door lintels (steel or concrete beams that support brickwork above an opening) to catch and divert water that penetrates the brickwork above the opening.
- Below Openings (Sills): Installed beneath window and door sills to prevent water from entering at the bottom of the opening.
- Shelf Angles and Ledges: In multi-story brick veneer construction, shelf angles are used to support intermediate brick courses. Flashing must be installed above these angles to manage water at each floor level.
- Parapet Walls: If the brick wall extends above the roofline (a parapet wall), flashing is required at the intersection of the roof and the wall, and often within the parapet itself, to prevent water intrusion.
- Intersections with Other Materials: Where the brick wall meets other building components like roofs, decks, or adjacent walls of different materials.
By diligently following these principles and incorporating high-quality materials and skilled workmanship, flashing will provide long-term protection against moisture damage in brick wall systems.
